gcc/libgo/runtime/mgc0.c

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// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Garbage collector.
#include <unistd.h>
#include "runtime.h"
#include "arch.h"
#include "malloc.h"
#include "mgc0.h"
#include "race.h"
#include "go-type.h"
// Map gccgo field names to gc field names.
// Slice aka __go_open_array.
#define array __values
#define cap __capacity
// Iface aka __go_interface
#define tab __methods
// Eface aka __go_empty_interface.
#define type __type_descriptor
// Hmap aka __go_map
typedef struct __go_map Hmap;
// Type aka __go_type_descriptor
#define kind __code
#define string __reflection
#define KindPtr GO_PTR
#define KindNoPointers GO_NO_POINTERS
// PtrType aka __go_ptr_type
#define elem __element_type
#ifdef USING_SPLIT_STACK
extern void * __splitstack_find (void *, void *, size_t *, void **, void **,
void **);
extern void * __splitstack_find_context (void *context[10], size_t *, void **,
void **, void **);
#endif
enum {
Debug = 0,
DebugMark = 0, // run second pass to check mark
CollectStats = 0,
ScanStackByFrames = 0,
IgnorePreciseGC = 0,
// Four bits per word (see #defines below).
wordsPerBitmapWord = sizeof(void*)*8/4,
bitShift = sizeof(void*)*8/4,
handoffThreshold = 4,
IntermediateBufferCapacity = 64,
// Bits in type information
PRECISE = 1,
LOOP = 2,
PC_BITS = PRECISE | LOOP,
// Pointer map
BitsPerPointer = 2,
BitsNoPointer = 0,
BitsPointer = 1,
BitsIface = 2,
BitsEface = 3,
};
// Bits in per-word bitmap.
// #defines because enum might not be able to hold the values.
//
// Each word in the bitmap describes wordsPerBitmapWord words
// of heap memory. There are 4 bitmap bits dedicated to each heap word,
// so on a 64-bit system there is one bitmap word per 16 heap words.
// The bits in the word are packed together by type first, then by
// heap location, so each 64-bit bitmap word consists of, from top to bottom,
// the 16 bitSpecial bits for the corresponding heap words, then the 16 bitMarked bits,
// then the 16 bitNoScan/bitBlockBoundary bits, then the 16 bitAllocated bits.
// This layout makes it easier to iterate over the bits of a given type.
//
// The bitmap starts at mheap.arena_start and extends *backward* from
// there. On a 64-bit system the off'th word in the arena is tracked by
// the off/16+1'th word before mheap.arena_start. (On a 32-bit system,
// the only difference is that the divisor is 8.)
//
// To pull out the bits corresponding to a given pointer p, we use:
//
// off = p - (uintptr*)mheap.arena_start; // word offset
// b = (uintptr*)mheap.arena_start - off/wordsPerBitmapWord - 1;
// shift = off % wordsPerBitmapWord
// bits = *b >> shift;
// /* then test bits & bitAllocated, bits & bitMarked, etc. */
//
#define bitAllocated ((uintptr)1<<(bitShift*0))
#define bitNoScan ((uintptr)1<<(bitShift*1)) /* when bitAllocated is set */
#define bitMarked ((uintptr)1<<(bitShift*2)) /* when bitAllocated is set */
#define bitSpecial ((uintptr)1<<(bitShift*3)) /* when bitAllocated is set - has finalizer or being profiled */
#define bitBlockBoundary ((uintptr)1<<(bitShift*1)) /* when bitAllocated is NOT set */
#define bitMask (bitBlockBoundary | bitAllocated | bitMarked | bitSpecial)
// Holding worldsema grants an M the right to try to stop the world.
// The procedure is:
//
// runtime_semacquire(&runtime_worldsema);
// m->gcing = 1;
// runtime_stoptheworld();
//
// ... do stuff ...
//
// m->gcing = 0;
// runtime_semrelease(&runtime_worldsema);
// runtime_starttheworld();
//
uint32 runtime_worldsema = 1;
// The size of Workbuf is N*PageSize.
typedef struct Workbuf Workbuf;
struct Workbuf
{
#define SIZE (2*PageSize-sizeof(LFNode)-sizeof(uintptr))
LFNode node; // must be first
uintptr nobj;
Obj obj[SIZE/sizeof(Obj) - 1];
uint8 _padding[SIZE%sizeof(Obj) + sizeof(Obj)];
#undef SIZE
};
typedef struct Finalizer Finalizer;
struct Finalizer
{
FuncVal *fn;
void *arg;
const struct __go_func_type *ft;
const struct __go_ptr_type *ot;
};
typedef struct FinBlock FinBlock;
struct FinBlock
{
FinBlock *alllink;
FinBlock *next;
int32 cnt;
int32 cap;
Finalizer fin[1];
};
static G *fing;
static FinBlock *finq; // list of finalizers that are to be executed
static FinBlock *finc; // cache of free blocks
static FinBlock *allfin; // list of all blocks
static Lock finlock;
static int32 fingwait;
static void runfinq(void*);
static Workbuf* getempty(Workbuf*);
static Workbuf* getfull(Workbuf*);
static void putempty(Workbuf*);
static Workbuf* handoff(Workbuf*);
static void gchelperstart(void);
static struct {
uint64 full; // lock-free list of full blocks
uint64 empty; // lock-free list of empty blocks
byte pad0[CacheLineSize]; // prevents false-sharing between full/empty and nproc/nwait
uint32 nproc;
volatile uint32 nwait;
volatile uint32 ndone;
volatile uint32 debugmarkdone;
Note alldone;
ParFor *markfor;
ParFor *sweepfor;
Lock;
byte *chunk;
uintptr nchunk;
Obj *roots;
uint32 nroot;
uint32 rootcap;
} work __attribute__((aligned(8)));
enum {
GC_DEFAULT_PTR = GC_NUM_INSTR,
GC_CHAN,
GC_NUM_INSTR2
};
static struct {
struct {
uint64 sum;
uint64 cnt;
} ptr;
uint64 nbytes;
struct {
uint64 sum;
uint64 cnt;
uint64 notype;
uint64 typelookup;
} obj;
uint64 rescan;
uint64 rescanbytes;
uint64 instr[GC_NUM_INSTR2];
uint64 putempty;
uint64 getfull;
struct {
uint64 foundbit;
uint64 foundword;
uint64 foundspan;
} flushptrbuf;
struct {
uint64 foundbit;
uint64 foundword;
uint64 foundspan;
} markonly;
} gcstats;
// markonly marks an object. It returns true if the object
// has been marked by this function, false otherwise.
// This function doesn't append the object to any buffer.
static bool
markonly(void *obj)
{
byte *p;
uintptr *bitp, bits, shift, x, xbits, off, j;
MSpan *s;
PageID k;
// Words outside the arena cannot be pointers.
if((byte*)obj < runtime_mheap.arena_start || (byte*)obj >= runtime_mheap.arena_used)
return false;
// obj may be a pointer to a live object.
// Try to find the beginning of the object.
// Round down to word boundary.
obj = (void*)((uintptr)obj & ~((uintptr)PtrSize-1));
// Find bits for this word.
off = (uintptr*)obj - (uintptr*)runtime_mheap.arena_start;
bitp = (uintptr*)runtime_mheap.arena_start - off/wordsPerBitmapWord - 1;
shift = off % wordsPerBitmapWord;
xbits = *bitp;
bits = xbits >> shift;
// Pointing at the beginning of a block?
if((bits & (bitAllocated|bitBlockBoundary)) != 0) {
if(CollectStats)
runtime_xadd64(&gcstats.markonly.foundbit, 1);
goto found;
}
// Pointing just past the beginning?
// Scan backward a little to find a block boundary.
for(j=shift; j-->0; ) {
if(((xbits>>j) & (bitAllocated|bitBlockBoundary)) != 0) {
shift = j;
bits = xbits>>shift;
if(CollectStats)
runtime_xadd64(&gcstats.markonly.foundword, 1);
goto found;
}
}
// Otherwise consult span table to find beginning.
// (Manually inlined copy of MHeap_LookupMaybe.)
k = (uintptr)obj>>PageShift;
x = k;
x -= (uintptr)runtime_mheap.arena_start>>PageShift;
s = runtime_mheap.spans[x];
if(s == nil || k < s->start || (byte*)obj >= s->limit || s->state != MSpanInUse)
return false;
p = (byte*)((uintptr)s->start<<PageShift);
if(s->sizeclass == 0) {
obj = p;
} else {
uintptr size = s->elemsize;
int32 i = ((byte*)obj - p)/size;
obj = p+i*size;
}
// Now that we know the object header, reload bits.
off = (uintptr*)obj - (uintptr*)runtime_mheap.arena_start;
bitp = (uintptr*)runtime_mheap.arena_start - off/wordsPerBitmapWord - 1;
shift = off % wordsPerBitmapWord;
xbits = *bitp;
bits = xbits >> shift;
if(CollectStats)
runtime_xadd64(&gcstats.markonly.foundspan, 1);
found:
// Now we have bits, bitp, and shift correct for
// obj pointing at the base of the object.
// Only care about allocated and not marked.
if((bits & (bitAllocated|bitMarked)) != bitAllocated)
return false;
if(work.nproc == 1)
*bitp |= bitMarked<<shift;
else {
for(;;) {
x = *bitp;
if(x & (bitMarked<<shift))
return false;
if(runtime_casp((void**)bitp, (void*)x, (void*)(x|(bitMarked<<shift))))
break;
}
}
// The object is now marked
return true;
}
// PtrTarget is a structure used by intermediate buffers.
// The intermediate buffers hold GC data before it
// is moved/flushed to the work buffer (Workbuf).
// The size of an intermediate buffer is very small,
// such as 32 or 64 elements.
typedef struct PtrTarget PtrTarget;
struct PtrTarget
{
void *p;
uintptr ti;
};
typedef struct BufferList BufferList;
struct BufferList
{
PtrTarget ptrtarget[IntermediateBufferCapacity];
Obj obj[IntermediateBufferCapacity];
uint32 busy;
byte pad[CacheLineSize];
};
static BufferList bufferList[MaxGcproc];
static Type *itabtype;
static void enqueue(Obj obj, Workbuf **_wbuf, Obj **_wp, uintptr *_nobj);
// flushptrbuf moves data from the PtrTarget buffer to the work buffer.
// The PtrTarget buffer contains blocks irrespective of whether the blocks have been marked or scanned,
// while the work buffer contains blocks which have been marked
// and are prepared to be scanned by the garbage collector.
//
// _wp, _wbuf, _nobj are input/output parameters and are specifying the work buffer.
//
// A simplified drawing explaining how the todo-list moves from a structure to another:
//
// scanblock
// (find pointers)
// Obj ------> PtrTarget (pointer targets)
// ↑ |
// | |
// `----------'
// flushptrbuf
// (find block start, mark and enqueue)
static void
flushptrbuf(PtrTarget *ptrbuf, PtrTarget **ptrbufpos, Obj **_wp, Workbuf **_wbuf, uintptr *_nobj)
{
byte *p, *arena_start, *obj;
uintptr size, *bitp, bits, shift, j, x, xbits, off, nobj, ti, n;
MSpan *s;
PageID k;
Obj *wp;
Workbuf *wbuf;
PtrTarget *ptrbuf_end;
arena_start = runtime_mheap.arena_start;
wp = *_wp;
wbuf = *_wbuf;
nobj = *_nobj;
ptrbuf_end = *ptrbufpos;
n = ptrbuf_end - ptrbuf;
*ptrbufpos = ptrbuf;
if(CollectStats) {
runtime_xadd64(&gcstats.ptr.sum, n);
runtime_xadd64(&gcstats.ptr.cnt, 1);
}
// If buffer is nearly full, get a new one.
if(wbuf == nil || nobj+n >= nelem(wbuf->obj)) {
if(wbuf != nil)
wbuf->nobj = nobj;
wbuf = getempty(wbuf);
wp = wbuf->obj;
nobj = 0;
if(n >= nelem(wbuf->obj))
runtime_throw("ptrbuf has to be smaller than WorkBuf");
}
// TODO(atom): This block is a branch of an if-then-else statement.
// The single-threaded branch may be added in a next CL.
{
// Multi-threaded version.
while(ptrbuf < ptrbuf_end) {
obj = ptrbuf->p;
ti = ptrbuf->ti;
ptrbuf++;
// obj belongs to interval [mheap.arena_start, mheap.arena_used).
if(Debug > 1) {
if(obj < runtime_mheap.arena_start || obj >= runtime_mheap.arena_used)
runtime_throw("object is outside of mheap");
}
// obj may be a pointer to a live object.
// Try to find the beginning of the object.
// Round down to word boundary.
if(((uintptr)obj & ((uintptr)PtrSize-1)) != 0) {
obj = (void*)((uintptr)obj & ~((uintptr)PtrSize-1));
ti = 0;
}
// Find bits for this word.
off = (uintptr*)obj - (uintptr*)arena_start;
bitp = (uintptr*)arena_start - off/wordsPerBitmapWord - 1;
shift = off % wordsPerBitmapWord;
xbits = *bitp;
bits = xbits >> shift;
// Pointing at the beginning of a block?
if((bits & (bitAllocated|bitBlockBoundary)) != 0) {
if(CollectStats)
runtime_xadd64(&gcstats.flushptrbuf.foundbit, 1);
goto found;
}
ti = 0;
// Pointing just past the beginning?
// Scan backward a little to find a block boundary.
for(j=shift; j-->0; ) {
if(((xbits>>j) & (bitAllocated|bitBlockBoundary)) != 0) {
obj = (byte*)obj - (shift-j)*PtrSize;
shift = j;
bits = xbits>>shift;
if(CollectStats)
runtime_xadd64(&gcstats.flushptrbuf.foundword, 1);
goto found;
}
}
// Otherwise consult span table to find beginning.
// (Manually inlined copy of MHeap_LookupMaybe.)
k = (uintptr)obj>>PageShift;
x = k;
x -= (uintptr)arena_start>>PageShift;
s = runtime_mheap.spans[x];
if(s == nil || k < s->start || obj >= s->limit || s->state != MSpanInUse)
continue;
p = (byte*)((uintptr)s->start<<PageShift);
if(s->sizeclass == 0) {
obj = p;
} else {
size = s->elemsize;
int32 i = ((byte*)obj - p)/size;
obj = p+i*size;
}
// Now that we know the object header, reload bits.
off = (uintptr*)obj - (uintptr*)arena_start;
bitp = (uintptr*)arena_start - off/wordsPerBitmapWord - 1;
shift = off % wordsPerBitmapWord;
xbits = *bitp;
bits = xbits >> shift;
if(CollectStats)
runtime_xadd64(&gcstats.flushptrbuf.foundspan, 1);
found:
// Now we have bits, bitp, and shift correct for
// obj pointing at the base of the object.
// Only care about allocated and not marked.
if((bits & (bitAllocated|bitMarked)) != bitAllocated)
continue;
if(work.nproc == 1)
*bitp |= bitMarked<<shift;
else {
for(;;) {
x = *bitp;
if(x & (bitMarked<<shift))
goto continue_obj;
if(runtime_casp((void**)bitp, (void*)x, (void*)(x|(bitMarked<<shift))))
break;
}
}
// If object has no pointers, don't need to scan further.
if((bits & bitNoScan) != 0)
continue;
// Ask span about size class.
// (Manually inlined copy of MHeap_Lookup.)
x = (uintptr)obj >> PageShift;
x -= (uintptr)arena_start>>PageShift;
s = runtime_mheap.spans[x];
PREFETCH(obj);
*wp = (Obj){obj, s->elemsize, ti};
wp++;
nobj++;
continue_obj:;
}
// If another proc wants a pointer, give it some.
if(work.nwait > 0 && nobj > handoffThreshold && work.full == 0) {
wbuf->nobj = nobj;
wbuf = handoff(wbuf);
nobj = wbuf->nobj;
wp = wbuf->obj + nobj;
}
}
*_wp = wp;
*_wbuf = wbuf;
*_nobj = nobj;
}
static void
flushobjbuf(Obj *objbuf, Obj **objbufpos, Obj **_wp, Workbuf **_wbuf, uintptr *_nobj)
{
uintptr nobj, off;
Obj *wp, obj;
Workbuf *wbuf;
Obj *objbuf_end;
wp = *_wp;
wbuf = *_wbuf;
nobj = *_nobj;
objbuf_end = *objbufpos;
*objbufpos = objbuf;
while(objbuf < objbuf_end) {
obj = *objbuf++;
// Align obj.b to a word boundary.
off = (uintptr)obj.p & (PtrSize-1);
if(off != 0) {
obj.p += PtrSize - off;
obj.n -= PtrSize - off;
obj.ti = 0;
}
if(obj.p == nil || obj.n == 0)
continue;
// If buffer is full, get a new one.
if(wbuf == nil || nobj >= nelem(wbuf->obj)) {
if(wbuf != nil)
wbuf->nobj = nobj;
wbuf = getempty(wbuf);
wp = wbuf->obj;
nobj = 0;
}
*wp = obj;
wp++;
nobj++;
}
// If another proc wants a pointer, give it some.
if(work.nwait > 0 && nobj > handoffThreshold && work.full == 0) {
wbuf->nobj = nobj;
wbuf = handoff(wbuf);
nobj = wbuf->nobj;
wp = wbuf->obj + nobj;
}
*_wp = wp;
*_wbuf = wbuf;
*_nobj = nobj;
}
// Program that scans the whole block and treats every block element as a potential pointer
static uintptr defaultProg[2] = {PtrSize, GC_DEFAULT_PTR};
#if 0
// Hchan program
static uintptr chanProg[2] = {0, GC_CHAN};
#endif
// Local variables of a program fragment or loop
typedef struct Frame Frame;
struct Frame {
uintptr count, elemsize, b;
uintptr *loop_or_ret;
};
// Sanity check for the derived type info objti.
static void
checkptr(void *obj, uintptr objti)
{
uintptr type, tisize, i, x;
byte *objstart;
Type *t;
MSpan *s;
if(!Debug)
runtime_throw("checkptr is debug only");
if((byte*)obj < runtime_mheap.arena_start || (byte*)obj >= runtime_mheap.arena_used)
return;
type = runtime_gettype(obj);
t = (Type*)(type & ~(uintptr)(PtrSize-1));
if(t == nil)
return;
x = (uintptr)obj >> PageShift;
x -= (uintptr)(runtime_mheap.arena_start)>>PageShift;
s = runtime_mheap.spans[x];
objstart = (byte*)((uintptr)s->start<<PageShift);
if(s->sizeclass != 0) {
i = ((byte*)obj - objstart)/s->elemsize;
objstart += i*s->elemsize;
}
tisize = *(uintptr*)objti;
// Sanity check for object size: it should fit into the memory block.
if((byte*)obj + tisize > objstart + s->elemsize) {
runtime_printf("object of type '%S' at %p/%p does not fit in block %p/%p\n",
*t->string, obj, tisize, objstart, s->elemsize);
runtime_throw("invalid gc type info");
}
if(obj != objstart)
return;
// If obj points to the beginning of the memory block,
// check type info as well.
if(t->string == nil ||
// Gob allocates unsafe pointers for indirection.
(runtime_strcmp((const char *)t->string->str, (const char*)"unsafe.Pointer") &&
// Runtime and gc think differently about closures.
runtime_strstr((const char *)t->string->str, (const char*)"struct { F uintptr") != (const char *)t->string->str)) {
#if 0
pc1 = (uintptr*)objti;
pc2 = (uintptr*)t->gc;
// A simple best-effort check until first GC_END.
for(j = 1; pc1[j] != GC_END && pc2[j] != GC_END; j++) {
if(pc1[j] != pc2[j]) {
runtime_printf("invalid gc type info for '%s' at %p, type info %p, block info %p\n",
t->string ? (const int8*)t->string->str : (const int8*)"?", j, pc1[j], pc2[j]);
runtime_throw("invalid gc type info");
}
}
#endif
}
}
// scanblock scans a block of n bytes starting at pointer b for references
// to other objects, scanning any it finds recursively until there are no
// unscanned objects left. Instead of using an explicit recursion, it keeps
// a work list in the Workbuf* structures and loops in the main function
// body. Keeping an explicit work list is easier on the stack allocator and
// more efficient.
//
// wbuf: current work buffer
// wp: storage for next queued pointer (write pointer)
// nobj: number of queued objects
static void
scanblock(Workbuf *wbuf, Obj *wp, uintptr nobj, bool keepworking)
{
byte *b, *arena_start, *arena_used;
uintptr n, i, end_b, elemsize, size, ti, objti, count /* , type */;
uintptr *pc, precise_type, nominal_size;
#if 0
uintptr *chan_ret, chancap;
#endif
void *obj;
const Type *t;
Slice *sliceptr;
Frame *stack_ptr, stack_top, stack[GC_STACK_CAPACITY+4];
BufferList *scanbuffers;
PtrTarget *ptrbuf, *ptrbuf_end, *ptrbufpos;
Obj *objbuf, *objbuf_end, *objbufpos;
Eface *eface;
Iface *iface;
#if 0
Hchan *chan;
ChanType *chantype;
#endif
if(sizeof(Workbuf) % PageSize != 0)
runtime_throw("scanblock: size of Workbuf is suboptimal");
// Memory arena parameters.
arena_start = runtime_mheap.arena_start;
arena_used = runtime_mheap.arena_used;
stack_ptr = stack+nelem(stack)-1;
precise_type = false;
nominal_size = 0;
// Allocate ptrbuf
{
scanbuffers = &bufferList[runtime_m()->helpgc];
ptrbuf = &scanbuffers->ptrtarget[0];
ptrbuf_end = &scanbuffers->ptrtarget[0] + nelem(scanbuffers->ptrtarget);
objbuf = &scanbuffers->obj[0];
objbuf_end = &scanbuffers->obj[0] + nelem(scanbuffers->obj);
}
ptrbufpos = ptrbuf;
objbufpos = objbuf;
// (Silence the compiler)
#if 0
chan = nil;
chantype = nil;
chan_ret = nil;
#endif
goto next_block;
for(;;) {
// Each iteration scans the block b of length n, queueing pointers in
// the work buffer.
if(Debug > 1) {
runtime_printf("scanblock %p %D\n", b, (int64)n);
}
if(CollectStats) {
runtime_xadd64(&gcstats.nbytes, n);
runtime_xadd64(&gcstats.obj.sum, nobj);
runtime_xadd64(&gcstats.obj.cnt, 1);
}
if(ti != 0 && false) {
pc = (uintptr*)(ti & ~(uintptr)PC_BITS);
precise_type = (ti & PRECISE);
stack_top.elemsize = pc[0];
if(!precise_type)
nominal_size = pc[0];
if(ti & LOOP) {
stack_top.count = 0; // 0 means an infinite number of iterations
stack_top.loop_or_ret = pc+1;
} else {
stack_top.count = 1;
}
if(Debug) {
// Simple sanity check for provided type info ti:
// The declared size of the object must be not larger than the actual size
// (it can be smaller due to inferior pointers).
// It's difficult to make a comprehensive check due to inferior pointers,
// reflection, gob, etc.
if(pc[0] > n) {
runtime_printf("invalid gc type info: type info size %p, block size %p\n", pc[0], n);
runtime_throw("invalid gc type info");
}
}
} else if(UseSpanType && false) {
if(CollectStats)
runtime_xadd64(&gcstats.obj.notype, 1);
#if 0
type = runtime_gettype(b);
if(type != 0) {
if(CollectStats)
runtime_xadd64(&gcstats.obj.typelookup, 1);
t = (Type*)(type & ~(uintptr)(PtrSize-1));
switch(type & (PtrSize-1)) {
case TypeInfo_SingleObject:
pc = (uintptr*)t->gc;
precise_type = true; // type information about 'b' is precise
stack_top.count = 1;
stack_top.elemsize = pc[0];
break;
case TypeInfo_Array:
pc = (uintptr*)t->gc;
if(pc[0] == 0)
goto next_block;
precise_type = true; // type information about 'b' is precise
stack_top.count = 0; // 0 means an infinite number of iterations
stack_top.elemsize = pc[0];
stack_top.loop_or_ret = pc+1;
break;
case TypeInfo_Chan:
chan = (Hchan*)b;
chantype = (ChanType*)t;
chan_ret = nil;
pc = chanProg;
break;
default:
runtime_throw("scanblock: invalid type");
return;
}
} else {
pc = defaultProg;
}
#endif
} else {
pc = defaultProg;
}
if(IgnorePreciseGC)
pc = defaultProg;
pc++;
stack_top.b = (uintptr)b;
end_b = (uintptr)b + n - PtrSize;
for(;;) {
if(CollectStats)
runtime_xadd64(&gcstats.instr[pc[0]], 1);
obj = nil;
objti = 0;
switch(pc[0]) {
case GC_PTR:
obj = *(void**)(stack_top.b + pc[1]);
objti = pc[2];
pc += 3;
if(Debug)
checkptr(obj, objti);
break;
case GC_SLICE:
sliceptr = (Slice*)(stack_top.b + pc[1]);
if(sliceptr->cap != 0) {
obj = sliceptr->array;
// Can't use slice element type for scanning,
// because if it points to an array embedded
// in the beginning of a struct,
// we will scan the whole struct as the slice.
// So just obtain type info from heap.
}
pc += 3;
break;
case GC_APTR:
obj = *(void**)(stack_top.b + pc[1]);
pc += 2;
break;
case GC_STRING:
obj = *(void**)(stack_top.b + pc[1]);
markonly(obj);
pc += 2;
continue;
case GC_EFACE:
eface = (Eface*)(stack_top.b + pc[1]);
pc += 2;
if(eface->type == nil)
continue;
// eface->type
t = eface->type;
if((const byte*)t >= arena_start && (const byte*)t < arena_used) {
union { const Type *tc; Type *tr; } u;
u.tc = t;
*ptrbufpos++ = (struct PtrTarget){(void*)u.tr, 0};
if(ptrbufpos == ptrbuf_end)
flushptrbuf(ptrbuf, &ptrbufpos, &wp, &wbuf, &nobj);
}
// eface->__object
if((byte*)eface->__object >= arena_start && (byte*)eface->__object < arena_used) {
if(t->__size <= sizeof(void*)) {
if((t->kind & KindNoPointers))
continue;
obj = eface->__object;
if((t->kind & ~KindNoPointers) == KindPtr)
// objti = (uintptr)((PtrType*)t)->elem->gc;
objti = 0;
} else {
obj = eface->__object;
// objti = (uintptr)t->gc;
objti = 0;
}
}
break;
case GC_IFACE:
iface = (Iface*)(stack_top.b + pc[1]);
pc += 2;
if(iface->tab == nil)
continue;
// iface->tab
if((byte*)iface->tab >= arena_start && (byte*)iface->tab < arena_used) {
// *ptrbufpos++ = (struct PtrTarget){iface->tab, (uintptr)itabtype->gc};
*ptrbufpos++ = (struct PtrTarget){iface->tab, 0};
if(ptrbufpos == ptrbuf_end)
flushptrbuf(ptrbuf, &ptrbufpos, &wp, &wbuf, &nobj);
}
// iface->data
if((byte*)iface->__object >= arena_start && (byte*)iface->__object < arena_used) {
// t = iface->tab->type;
t = nil;
if(t->__size <= sizeof(void*)) {
if((t->kind & KindNoPointers))
continue;
obj = iface->__object;
if((t->kind & ~KindNoPointers) == KindPtr)
// objti = (uintptr)((const PtrType*)t)->elem->gc;
objti = 0;
} else {
obj = iface->__object;
// objti = (uintptr)t->gc;
objti = 0;
}
}
break;
case GC_DEFAULT_PTR:
while(stack_top.b <= end_b) {
obj = *(byte**)stack_top.b;
stack_top.b += PtrSize;
if((byte*)obj >= arena_start && (byte*)obj < arena_used) {
*ptrbufpos++ = (struct PtrTarget){obj, 0};
if(ptrbufpos == ptrbuf_end)
flushptrbuf(ptrbuf, &ptrbufpos, &wp, &wbuf, &nobj);
}
}
goto next_block;
case GC_END:
if(--stack_top.count != 0) {
// Next iteration of a loop if possible.
stack_top.b += stack_top.elemsize;
if(stack_top.b + stack_top.elemsize <= end_b+PtrSize) {
pc = stack_top.loop_or_ret;
continue;
}
i = stack_top.b;
} else {
// Stack pop if possible.
if(stack_ptr+1 < stack+nelem(stack)) {
pc = stack_top.loop_or_ret;
stack_top = *(++stack_ptr);
continue;
}
i = (uintptr)b + nominal_size;
}
if(!precise_type) {
// Quickly scan [b+i,b+n) for possible pointers.
for(; i<=end_b; i+=PtrSize) {
if(*(byte**)i != nil) {
// Found a value that may be a pointer.
// Do a rescan of the entire block.
enqueue((Obj){b, n, 0}, &wbuf, &wp, &nobj);
if(CollectStats) {
runtime_xadd64(&gcstats.rescan, 1);
runtime_xadd64(&gcstats.rescanbytes, n);
}
break;
}
}
}
goto next_block;
case GC_ARRAY_START:
i = stack_top.b + pc[1];
count = pc[2];
elemsize = pc[3];
pc += 4;
// Stack push.
*stack_ptr-- = stack_top;
stack_top = (Frame){count, elemsize, i, pc};
continue;
case GC_ARRAY_NEXT:
if(--stack_top.count != 0) {
stack_top.b += stack_top.elemsize;
pc = stack_top.loop_or_ret;
} else {
// Stack pop.
stack_top = *(++stack_ptr);
pc += 1;
}
continue;
case GC_CALL:
// Stack push.
*stack_ptr-- = stack_top;
stack_top = (Frame){1, 0, stack_top.b + pc[1], pc+3 /*return address*/};
pc = (uintptr*)((byte*)pc + *(int32*)(pc+2)); // target of the CALL instruction
continue;
case GC_REGION:
obj = (void*)(stack_top.b + pc[1]);
size = pc[2];
objti = pc[3];
pc += 4;
*objbufpos++ = (Obj){obj, size, objti};
if(objbufpos == objbuf_end)
flushobjbuf(objbuf, &objbufpos, &wp, &wbuf, &nobj);
continue;
#if 0
case GC_CHAN_PTR:
chan = *(Hchan**)(stack_top.b + pc[1]);
if(chan == nil) {
pc += 3;
continue;
}
if(markonly(chan)) {
chantype = (ChanType*)pc[2];
if(!(chantype->elem->kind & KindNoPointers)) {
// Start chanProg.
chan_ret = pc+3;
pc = chanProg+1;
continue;
}
}
pc += 3;
continue;
case GC_CHAN:
// There are no heap pointers in struct Hchan,
// so we can ignore the leading sizeof(Hchan) bytes.
if(!(chantype->elem->kind & KindNoPointers)) {
// Channel's buffer follows Hchan immediately in memory.
// Size of buffer (cap(c)) is second int in the chan struct.
chancap = ((uintgo*)chan)[1];
if(chancap > 0) {
// TODO(atom): split into two chunks so that only the
// in-use part of the circular buffer is scanned.
// (Channel routines zero the unused part, so the current
// code does not lead to leaks, it's just a little inefficient.)
*objbufpos++ = (Obj){(byte*)chan+runtime_Hchansize, chancap*chantype->elem->size,
(uintptr)chantype->elem->gc | PRECISE | LOOP};
if(objbufpos == objbuf_end)
flushobjbuf(objbuf, &objbufpos, &wp, &wbuf, &nobj);
}
}
if(chan_ret == nil)
goto next_block;
pc = chan_ret;
continue;
#endif
default:
runtime_throw("scanblock: invalid GC instruction");
return;
}
if((byte*)obj >= arena_start && (byte*)obj < arena_used) {
*ptrbufpos++ = (struct PtrTarget){obj, objti};
if(ptrbufpos == ptrbuf_end)
flushptrbuf(ptrbuf, &ptrbufpos, &wp, &wbuf, &nobj);
}
}
next_block:
// Done scanning [b, b+n). Prepare for the next iteration of
// the loop by setting b, n, ti to the parameters for the next block.
if(nobj == 0) {
flushptrbuf(ptrbuf, &ptrbufpos, &wp, &wbuf, &nobj);
flushobjbuf(objbuf, &objbufpos, &wp, &wbuf, &nobj);
if(nobj == 0) {
if(!keepworking) {
if(wbuf)
putempty(wbuf);
goto endscan;
}
// Emptied our buffer: refill.
wbuf = getfull(wbuf);
if(wbuf == nil)
goto endscan;
nobj = wbuf->nobj;
wp = wbuf->obj + wbuf->nobj;
}
}
// Fetch b from the work buffer.
--wp;
b = wp->p;
n = wp->n;
ti = wp->ti;
nobj--;
}
endscan:;
}
// debug_scanblock is the debug copy of scanblock.
// it is simpler, slower, single-threaded, recursive,
// and uses bitSpecial as the mark bit.
static void
debug_scanblock(byte *b, uintptr n)
{
byte *obj, *p;
void **vp;
uintptr size, *bitp, bits, shift, i, xbits, off;
MSpan *s;
if(!DebugMark)
runtime_throw("debug_scanblock without DebugMark");
if((intptr)n < 0) {
runtime_printf("debug_scanblock %p %D\n", b, (int64)n);
runtime_throw("debug_scanblock");
}
// Align b to a word boundary.
off = (uintptr)b & (PtrSize-1);
if(off != 0) {
b += PtrSize - off;
n -= PtrSize - off;
}
vp = (void**)b;
n /= PtrSize;
for(i=0; i<(uintptr)n; i++) {
obj = (byte*)vp[i];
// Words outside the arena cannot be pointers.
if((byte*)obj < runtime_mheap.arena_start || (byte*)obj >= runtime_mheap.arena_used)
continue;
// Round down to word boundary.
obj = (void*)((uintptr)obj & ~((uintptr)PtrSize-1));
// Consult span table to find beginning.
s = runtime_MHeap_LookupMaybe(&runtime_mheap, obj);
if(s == nil)
continue;
p = (byte*)((uintptr)s->start<<PageShift);
size = s->elemsize;
if(s->sizeclass == 0) {
obj = p;
} else {
int32 i = ((byte*)obj - p)/size;
obj = p+i*size;
}
// Now that we know the object header, reload bits.
off = (uintptr*)obj - (uintptr*)runtime_mheap.arena_start;
bitp = (uintptr*)runtime_mheap.arena_start - off/wordsPerBitmapWord - 1;
shift = off % wordsPerBitmapWord;
xbits = *bitp;
bits = xbits >> shift;
// Now we have bits, bitp, and shift correct for
// obj pointing at the base of the object.
// If not allocated or already marked, done.
if((bits & bitAllocated) == 0 || (bits & bitSpecial) != 0) // NOTE: bitSpecial not bitMarked
continue;
*bitp |= bitSpecial<<shift;
if(!(bits & bitMarked))
runtime_printf("found unmarked block %p in %p\n", obj, vp+i);
// If object has no pointers, don't need to scan further.
if((bits & bitNoScan) != 0)
continue;
debug_scanblock(obj, size);
}
}
// Append obj to the work buffer.
// _wbuf, _wp, _nobj are input/output parameters and are specifying the work buffer.
static void
enqueue(Obj obj, Workbuf **_wbuf, Obj **_wp, uintptr *_nobj)
{
uintptr nobj, off;
Obj *wp;
Workbuf *wbuf;
if(Debug > 1)
runtime_printf("append obj(%p %D %p)\n", obj.p, (int64)obj.n, obj.ti);
// Align obj.b to a word boundary.
off = (uintptr)obj.p & (PtrSize-1);
if(off != 0) {
obj.p += PtrSize - off;
obj.n -= PtrSize - off;
obj.ti = 0;
}
if(obj.p == nil || obj.n == 0)
return;
// Load work buffer state
wp = *_wp;
wbuf = *_wbuf;
nobj = *_nobj;
// If another proc wants a pointer, give it some.
if(work.nwait > 0 && nobj > handoffThreshold && work.full == 0) {
wbuf->nobj = nobj;
wbuf = handoff(wbuf);
nobj = wbuf->nobj;
wp = wbuf->obj + nobj;
}
// If buffer is full, get a new one.
if(wbuf == nil || nobj >= nelem(wbuf->obj)) {
if(wbuf != nil)
wbuf->nobj = nobj;
wbuf = getempty(wbuf);
wp = wbuf->obj;
nobj = 0;
}
*wp = obj;
wp++;
nobj++;
// Save work buffer state
*_wp = wp;
*_wbuf = wbuf;
*_nobj = nobj;
}
static void
markroot(ParFor *desc, uint32 i)
{
Obj *wp;
Workbuf *wbuf;
uintptr nobj;
USED(&desc);
wp = nil;
wbuf = nil;
nobj = 0;
enqueue(work.roots[i], &wbuf, &wp, &nobj);
scanblock(wbuf, wp, nobj, false);
}
// Get an empty work buffer off the work.empty list,
// allocating new buffers as needed.
static Workbuf*
getempty(Workbuf *b)
{
if(b != nil)
runtime_lfstackpush(&work.full, &b->node);
b = (Workbuf*)runtime_lfstackpop(&work.empty);
if(b == nil) {
// Need to allocate.
runtime_lock(&work);
if(work.nchunk < sizeof *b) {
work.nchunk = 1<<20;
work.chunk = runtime_SysAlloc(work.nchunk, &mstats.gc_sys);
if(work.chunk == nil)
runtime_throw("runtime: cannot allocate memory");
}
b = (Workbuf*)work.chunk;
work.chunk += sizeof *b;
work.nchunk -= sizeof *b;
runtime_unlock(&work);
}
b->nobj = 0;
return b;
}
static void
putempty(Workbuf *b)
{
if(CollectStats)
runtime_xadd64(&gcstats.putempty, 1);
runtime_lfstackpush(&work.empty, &b->node);
}
// Get a full work buffer off the work.full list, or return nil.
static Workbuf*
getfull(Workbuf *b)
{
M *m;
int32 i;
if(CollectStats)
runtime_xadd64(&gcstats.getfull, 1);
if(b != nil)
runtime_lfstackpush(&work.empty, &b->node);
b = (Workbuf*)runtime_lfstackpop(&work.full);
if(b != nil || work.nproc == 1)
return b;
m = runtime_m();
runtime_xadd(&work.nwait, +1);
for(i=0;; i++) {
if(work.full != 0) {
runtime_xadd(&work.nwait, -1);
b = (Workbuf*)runtime_lfstackpop(&work.full);
if(b != nil)
return b;
runtime_xadd(&work.nwait, +1);
}
if(work.nwait == work.nproc)
return nil;
if(i < 10) {
m->gcstats.nprocyield++;
runtime_procyield(20);
} else if(i < 20) {
m->gcstats.nosyield++;
runtime_osyield();
} else {
m->gcstats.nsleep++;
runtime_usleep(100);
}
}
}
static Workbuf*
handoff(Workbuf *b)
{
M *m;
int32 n;
Workbuf *b1;
m = runtime_m();
// Make new buffer with half of b's pointers.
b1 = getempty(nil);
n = b->nobj/2;
b->nobj -= n;
b1->nobj = n;
runtime_memmove(b1->obj, b->obj+b->nobj, n*sizeof b1->obj[0]);
m->gcstats.nhandoff++;
m->gcstats.nhandoffcnt += n;
// Put b on full list - let first half of b get stolen.
runtime_lfstackpush(&work.full, &b->node);
return b1;
}
static void
addroot(Obj obj)
{
uint32 cap;
Obj *new;
if(work.nroot >= work.rootcap) {
cap = PageSize/sizeof(Obj);
if(cap < 2*work.rootcap)
cap = 2*work.rootcap;
new = (Obj*)runtime_SysAlloc(cap*sizeof(Obj), &mstats.gc_sys);
if(new == nil)
runtime_throw("runtime: cannot allocate memory");
if(work.roots != nil) {
runtime_memmove(new, work.roots, work.rootcap*sizeof(Obj));
runtime_SysFree(work.roots, work.rootcap*sizeof(Obj), &mstats.gc_sys);
}
work.roots = new;
work.rootcap = cap;
}
work.roots[work.nroot] = obj;
work.nroot++;
}
static void
addstackroots(G *gp)
{
#ifdef USING_SPLIT_STACK
M *mp;
void* sp;
size_t spsize;
void* next_segment;
void* next_sp;
void* initial_sp;
if(gp == runtime_g()) {
// Scanning our own stack.
sp = __splitstack_find(nil, nil, &spsize, &next_segment,
&next_sp, &initial_sp);
} else if((mp = gp->m) != nil && mp->helpgc) {
// gchelper's stack is in active use and has no interesting pointers.
return;
} else {
// Scanning another goroutine's stack.
// The goroutine is usually asleep (the world is stopped).
// The exception is that if the goroutine is about to enter or might
// have just exited a system call, it may be executing code such
// as schedlock and may have needed to start a new stack segment.
// Use the stack segment and stack pointer at the time of
// the system call instead, since that won't change underfoot.
if(gp->gcstack != nil) {
sp = gp->gcstack;
spsize = gp->gcstack_size;
next_segment = gp->gcnext_segment;
next_sp = gp->gcnext_sp;
initial_sp = gp->gcinitial_sp;
} else {
sp = __splitstack_find_context(&gp->stack_context[0],
&spsize, &next_segment,
&next_sp, &initial_sp);
}
}
if(sp != nil) {
addroot((Obj){sp, spsize, 0});
while((sp = __splitstack_find(next_segment, next_sp,
&spsize, &next_segment,
&next_sp, &initial_sp)) != nil)
addroot((Obj){sp, spsize, 0});
}
#else
M *mp;
byte* bottom;
byte* top;
if(gp == runtime_g()) {
// Scanning our own stack.
bottom = (byte*)&gp;
} else if((mp = gp->m) != nil && mp->helpgc) {
// gchelper's stack is in active use and has no interesting pointers.
return;
} else {
// Scanning another goroutine's stack.
// The goroutine is usually asleep (the world is stopped).
bottom = (byte*)gp->gcnext_sp;
if(bottom == nil)
return;
}
top = (byte*)gp->gcinitial_sp + gp->gcstack_size;
if(top > bottom)
addroot((Obj){bottom, top - bottom, 0});
else
addroot((Obj){top, bottom - top, 0});
#endif
}
static void
addfinroots(void *v)
{
uintptr size;
void *base;
size = 0;
if(!runtime_mlookup(v, (byte**)&base, &size, nil) || !runtime_blockspecial(base))
runtime_throw("mark - finalizer inconsistency");
// do not mark the finalizer block itself. just mark the things it points at.
addroot((Obj){base, size, 0});
}
static struct root_list* roots;
void
__go_register_gc_roots (struct root_list* r)
{
// FIXME: This needs locking if multiple goroutines can call
// dlopen simultaneously.
r->next = roots;
roots = r;
}
static void
addroots(void)
{
struct root_list *pl;
G *gp;
FinBlock *fb;
MSpan *s, **allspans;
uint32 spanidx;
work.nroot = 0;
// mark data+bss.
for(pl = roots; pl != nil; pl = pl->next) {
struct root* pr = &pl->roots[0];
while(1) {
void *decl = pr->decl;
if(decl == nil)
break;
addroot((Obj){decl, pr->size, 0});
pr++;
}
}
addroot((Obj){(byte*)&runtime_m0, sizeof runtime_m0, 0});
addroot((Obj){(byte*)&runtime_g0, sizeof runtime_g0, 0});
addroot((Obj){(byte*)&runtime_allg, sizeof runtime_allg, 0});
addroot((Obj){(byte*)&runtime_allm, sizeof runtime_allm, 0});
addroot((Obj){(byte*)&runtime_allp, sizeof runtime_allp, 0});
runtime_proc_scan(addroot);
runtime_MProf_Mark(addroot);
runtime_time_scan(addroot);
runtime_netpoll_scan(addroot);
// MSpan.types
allspans = runtime_mheap.allspans;
for(spanidx=0; spanidx<runtime_mheap.nspan; spanidx++) {
s = allspans[spanidx];
if(s->state == MSpanInUse) {
// The garbage collector ignores type pointers stored in MSpan.types:
// - Compiler-generated types are stored outside of heap.
// - The reflect package has runtime-generated types cached in its data structures.
// The garbage collector relies on finding the references via that cache.
switch(s->types.compression) {
case MTypes_Empty:
case MTypes_Single:
break;
case MTypes_Words:
case MTypes_Bytes:
markonly((byte*)s->types.data);
break;
}
}
}
// stacks
for(gp=runtime_allg; gp!=nil; gp=gp->alllink) {
switch(gp->status){
default:
runtime_printf("unexpected G.status %d\n", gp->status);
runtime_throw("mark - bad status");
case Gdead:
break;
case Grunning:
runtime_throw("mark - world not stopped");
case Grunnable:
case Gsyscall:
case Gwaiting:
addstackroots(gp);
break;
}
}
runtime_walkfintab(addfinroots, addroot);
for(fb=allfin; fb; fb=fb->alllink)
addroot((Obj){(byte*)fb->fin, fb->cnt*sizeof(fb->fin[0]), 0});
addroot((Obj){(byte*)&work, sizeof work, 0});
}
static bool
handlespecial(byte *p, uintptr size)
{
FuncVal *fn;
const struct __go_func_type *ft;
const struct __go_ptr_type *ot;
FinBlock *block;
Finalizer *f;
if(!runtime_getfinalizer(p, true, &fn, &ft, &ot)) {
runtime_setblockspecial(p, false);
runtime_MProf_Free(p, size);
return false;
}
runtime_lock(&finlock);
if(finq == nil || finq->cnt == finq->cap) {
if(finc == nil) {
finc = runtime_persistentalloc(PageSize, 0, &mstats.gc_sys);
finc->cap = (PageSize - sizeof(FinBlock)) / sizeof(Finalizer) + 1;
finc->alllink = allfin;
allfin = finc;
}
block = finc;
finc = block->next;
block->next = finq;
finq = block;
}
f = &finq->fin[finq->cnt];
finq->cnt++;
f->fn = fn;
f->ft = ft;
f->ot = ot;
f->arg = p;
runtime_unlock(&finlock);
return true;
}
// Sweep frees or collects finalizers for blocks not marked in the mark phase.
// It clears the mark bits in preparation for the next GC round.
static void
sweepspan(ParFor *desc, uint32 idx)
{
M *m;
int32 cl, n, npages;
uintptr size;
byte *p;
MCache *c;
byte *arena_start;
MLink head, *end;
int32 nfree;
byte *type_data;
byte compression;
uintptr type_data_inc;
MSpan *s;
m = runtime_m();
USED(&desc);
s = runtime_mheap.allspans[idx];
if(s->state != MSpanInUse)
return;
arena_start = runtime_mheap.arena_start;
p = (byte*)(s->start << PageShift);
cl = s->sizeclass;
size = s->elemsize;
if(cl == 0) {
n = 1;
} else {
// Chunk full of small blocks.
npages = runtime_class_to_allocnpages[cl];
n = (npages << PageShift) / size;
}
nfree = 0;
end = &head;
c = m->mcache;
type_data = (byte*)s->types.data;
type_data_inc = sizeof(uintptr);
compression = s->types.compression;
switch(compression) {
case MTypes_Bytes:
type_data += 8*sizeof(uintptr);
type_data_inc = 1;
break;
}
// Sweep through n objects of given size starting at p.
// This thread owns the span now, so it can manipulate
// the block bitmap without atomic operations.
for(; n > 0; n--, p += size, type_data+=type_data_inc) {
uintptr off, *bitp, shift, bits;
off = (uintptr*)p - (uintptr*)arena_start;
bitp = (uintptr*)arena_start - off/wordsPerBitmapWord - 1;
shift = off % wordsPerBitmapWord;
bits = *bitp>>shift;
if((bits & bitAllocated) == 0)
continue;
if((bits & bitMarked) != 0) {
if(DebugMark) {
if(!(bits & bitSpecial))
runtime_printf("found spurious mark on %p\n", p);
*bitp &= ~(bitSpecial<<shift);
}
*bitp &= ~(bitMarked<<shift);
continue;
}
// Special means it has a finalizer or is being profiled.
// In DebugMark mode, the bit has been coopted so
// we have to assume all blocks are special.
if(DebugMark || (bits & bitSpecial) != 0) {
if(handlespecial(p, size))
continue;
}
// Mark freed; restore block boundary bit.
*bitp = (*bitp & ~(bitMask<<shift)) | (bitBlockBoundary<<shift);
if(cl == 0) {
// Free large span.
runtime_unmarkspan(p, 1<<PageShift);
*(uintptr*)p = (uintptr)0xdeaddeaddeaddeadll; // needs zeroing
runtime_MHeap_Free(&runtime_mheap, s, 1);
c->local_nlargefree++;
c->local_largefree += size;
} else {
// Free small object.
switch(compression) {
case MTypes_Words:
*(uintptr*)type_data = 0;
break;
case MTypes_Bytes:
*(byte*)type_data = 0;
break;
}
if(size > sizeof(uintptr))
((uintptr*)p)[1] = (uintptr)0xdeaddeaddeaddeadll; // mark as "needs to be zeroed"
end->next = (MLink*)p;
end = (MLink*)p;
nfree++;
}
}
if(nfree) {
c->local_nsmallfree[cl] += nfree;
c->local_cachealloc -= nfree * size;
runtime_MCentral_FreeSpan(&runtime_mheap.central[cl], s, nfree, head.next, end);
}
}
static void
dumpspan(uint32 idx)
{
int32 sizeclass, n, npages, i, column;
uintptr size;
byte *p;
byte *arena_start;
MSpan *s;
bool allocated, special;
s = runtime_mheap.allspans[idx];
if(s->state != MSpanInUse)
return;
arena_start = runtime_mheap.arena_start;
p = (byte*)(s->start << PageShift);
sizeclass = s->sizeclass;
size = s->elemsize;
if(sizeclass == 0) {
n = 1;
} else {
npages = runtime_class_to_allocnpages[sizeclass];
n = (npages << PageShift) / size;
}
runtime_printf("%p .. %p:\n", p, p+n*size);
column = 0;
for(; n>0; n--, p+=size) {
uintptr off, *bitp, shift, bits;
off = (uintptr*)p - (uintptr*)arena_start;
bitp = (uintptr*)arena_start - off/wordsPerBitmapWord - 1;
shift = off % wordsPerBitmapWord;
bits = *bitp>>shift;
allocated = ((bits & bitAllocated) != 0);
special = ((bits & bitSpecial) != 0);
for(i=0; (uint32)i<size; i+=sizeof(void*)) {
if(column == 0) {
runtime_printf("\t");
}
if(i == 0) {
runtime_printf(allocated ? "(" : "[");
runtime_printf(special ? "@" : "");
runtime_printf("%p: ", p+i);
} else {
runtime_printf(" ");
}
runtime_printf("%p", *(void**)(p+i));
if(i+sizeof(void*) >= size) {
runtime_printf(allocated ? ") " : "] ");
}
column++;
if(column == 8) {
runtime_printf("\n");
column = 0;
}
}
}
runtime_printf("\n");
}
// A debugging function to dump the contents of memory
void
runtime_memorydump(void)
{
uint32 spanidx;
for(spanidx=0; spanidx<runtime_mheap.nspan; spanidx++) {
dumpspan(spanidx);
}
}
void
runtime_gchelper(void)
{
uint32 nproc;
gchelperstart();
// parallel mark for over gc roots
runtime_parfordo(work.markfor);
// help other threads scan secondary blocks
scanblock(nil, nil, 0, true);
if(DebugMark) {
// wait while the main thread executes mark(debug_scanblock)
while(runtime_atomicload(&work.debugmarkdone) == 0)
runtime_usleep(10);
}
runtime_parfordo(work.sweepfor);
bufferList[runtime_m()->helpgc].busy = 0;
nproc = work.nproc; // work.nproc can change right after we increment work.ndone
if(runtime_xadd(&work.ndone, +1) == nproc-1)
runtime_notewakeup(&work.alldone);
}
#define GcpercentUnknown (-2)
// Initialized from $GOGC. GOGC=off means no gc.
//
// Next gc is after we've allocated an extra amount of
// memory proportional to the amount already in use.
// If gcpercent=100 and we're using 4M, we'll gc again
// when we get to 8M. This keeps the gc cost in linear
// proportion to the allocation cost. Adjusting gcpercent
// just changes the linear constant (and also the amount of
// extra memory used).
static int32 gcpercent = GcpercentUnknown;
static void
cachestats(void)
{
MCache *c;
P *p, **pp;
for(pp=runtime_allp; (p=*pp) != nil; pp++) {
c = p->mcache;
if(c==nil)
continue;
runtime_purgecachedstats(c);
}
}
static void
updatememstats(GCStats *stats)
{
M *mp;
MSpan *s;
MCache *c;
P *p, **pp;
uint32 i;
uint64 stacks_inuse, smallfree;
uint64 *src, *dst;
if(stats)
runtime_memclr((byte*)stats, sizeof(*stats));
stacks_inuse = 0;
for(mp=runtime_allm; mp; mp=mp->alllink) {
//stacks_inuse += mp->stackinuse*FixedStack;
if(stats) {
src = (uint64*)&mp->gcstats;
dst = (uint64*)stats;
for(i=0; i<sizeof(*stats)/sizeof(uint64); i++)
dst[i] += src[i];
runtime_memclr((byte*)&mp->gcstats, sizeof(mp->gcstats));
}
}
mstats.stacks_inuse = stacks_inuse;
mstats.mcache_inuse = runtime_mheap.cachealloc.inuse;
mstats.mspan_inuse = runtime_mheap.spanalloc.inuse;
mstats.sys = mstats.heap_sys + mstats.stacks_sys + mstats.mspan_sys +
mstats.mcache_sys + mstats.buckhash_sys + mstats.gc_sys + mstats.other_sys;
// Calculate memory allocator stats.
// During program execution we only count number of frees and amount of freed memory.
// Current number of alive object in the heap and amount of alive heap memory
// are calculated by scanning all spans.
// Total number of mallocs is calculated as number of frees plus number of alive objects.
// Similarly, total amount of allocated memory is calculated as amount of freed memory
// plus amount of alive heap memory.
mstats.alloc = 0;
mstats.total_alloc = 0;
mstats.nmalloc = 0;
mstats.nfree = 0;
for(i = 0; i < nelem(mstats.by_size); i++) {
mstats.by_size[i].nmalloc = 0;
mstats.by_size[i].nfree = 0;
}
// Flush MCache's to MCentral.
for(pp=runtime_allp; (p=*pp) != nil; pp++) {
c = p->mcache;
if(c==nil)
continue;
runtime_MCache_ReleaseAll(c);
}
// Aggregate local stats.
cachestats();
// Scan all spans and count number of alive objects.
for(i = 0; i < runtime_mheap.nspan; i++) {
s = runtime_mheap.allspans[i];
if(s->state != MSpanInUse)
continue;
if(s->sizeclass == 0) {
mstats.nmalloc++;
mstats.alloc += s->elemsize;
} else {
mstats.nmalloc += s->ref;
mstats.by_size[s->sizeclass].nmalloc += s->ref;
mstats.alloc += s->ref*s->elemsize;
}
}
// Aggregate by size class.
smallfree = 0;
mstats.nfree = runtime_mheap.nlargefree;
for(i = 0; i < nelem(mstats.by_size); i++) {
mstats.nfree += runtime_mheap.nsmallfree[i];
mstats.by_size[i].nfree = runtime_mheap.nsmallfree[i];
mstats.by_size[i].nmalloc += runtime_mheap.nsmallfree[i];
smallfree += runtime_mheap.nsmallfree[i] * runtime_class_to_size[i];
}
mstats.nmalloc += mstats.nfree;
// Calculate derived stats.
mstats.total_alloc = mstats.alloc + runtime_mheap.largefree + smallfree;
mstats.heap_alloc = mstats.alloc;
mstats.heap_objects = mstats.nmalloc - mstats.nfree;
}
// Structure of arguments passed to function gc().
// This allows the arguments to be passed via runtime_mcall.
struct gc_args
{
int64 start_time; // start time of GC in ns (just before stoptheworld)
};
static void gc(struct gc_args *args);
static void mgc(G *gp);
static int32
readgogc(void)
{
const byte *p;
p = runtime_getenv("GOGC");
if(p == nil || p[0] == '\0')
return 100;
if(runtime_strcmp((const char *)p, "off") == 0)
return -1;
return runtime_atoi(p);
}
void
runtime_gc(int32 force)
{
M *m;
G *g;
struct gc_args a;
int32 i;
// The atomic operations are not atomic if the uint64s
// are not aligned on uint64 boundaries. This has been
// a problem in the past.
if((((uintptr)&work.empty) & 7) != 0)
runtime_throw("runtime: gc work buffer is misaligned");
if((((uintptr)&work.full) & 7) != 0)
runtime_throw("runtime: gc work buffer is misaligned");
// Make sure all registers are saved on stack so that
// scanstack sees them.
__builtin_unwind_init();
// The gc is turned off (via enablegc) until
// the bootstrap has completed.
// Also, malloc gets called in the guts
// of a number of libraries that might be
// holding locks. To avoid priority inversion
// problems, don't bother trying to run gc
// while holding a lock. The next mallocgc
// without a lock will do the gc instead.
m = runtime_m();
if(!mstats.enablegc || runtime_g() == m->g0 || m->locks > 0 || runtime_panicking)
return;
if(gcpercent == GcpercentUnknown) { // first time through
runtime_lock(&runtime_mheap);
if(gcpercent == GcpercentUnknown)
gcpercent = readgogc();
runtime_unlock(&runtime_mheap);
}
if(gcpercent < 0)
return;
runtime_semacquire(&runtime_worldsema, false);
if(!force && mstats.heap_alloc < mstats.next_gc) {
// typically threads which lost the race to grab
// worldsema exit here when gc is done.
runtime_semrelease(&runtime_worldsema);
return;
}
// Ok, we're doing it! Stop everybody else
a.start_time = runtime_nanotime();
m->gcing = 1;
runtime_stoptheworld();
// Run gc on the g0 stack. We do this so that the g stack
// we're currently running on will no longer change. Cuts
// the root set down a bit (g0 stacks are not scanned, and
// we don't need to scan gc's internal state). Also an
// enabler for copyable stacks.
for(i = 0; i < (runtime_debug.gctrace > 1 ? 2 : 1); i++) {
// switch to g0, call gc(&a), then switch back
g = runtime_g();
g->param = &a;
g->status = Gwaiting;
g->waitreason = "garbage collection";
runtime_mcall(mgc);
// record a new start time in case we're going around again
a.start_time = runtime_nanotime();
}
// all done
m->gcing = 0;
m->locks++;
runtime_semrelease(&runtime_worldsema);
runtime_starttheworld();
m->locks--;
// now that gc is done, kick off finalizer thread if needed
if(finq != nil) {
runtime_lock(&finlock);
// kick off or wake up goroutine to run queued finalizers
if(fing == nil)
fing = __go_go(runfinq, nil);
else if(fingwait) {
fingwait = 0;
runtime_ready(fing);
}
runtime_unlock(&finlock);
}
// give the queued finalizers, if any, a chance to run
runtime_gosched();
}
static void
mgc(G *gp)
{
gc(gp->param);
gp->param = nil;
gp->status = Grunning;
runtime_gogo(gp);
}
static void
gc(struct gc_args *args)
{
M *m;
int64 t0, t1, t2, t3, t4;
uint64 heap0, heap1, obj0, obj1, ninstr;
GCStats stats;
M *mp;
uint32 i;
// Eface eface;
m = runtime_m();
t0 = args->start_time;
if(CollectStats)
runtime_memclr((byte*)&gcstats, sizeof(gcstats));
for(mp=runtime_allm; mp; mp=mp->alllink)
runtime_settype_flush(mp);
heap0 = 0;
obj0 = 0;
if(runtime_debug.gctrace) {
updatememstats(nil);
heap0 = mstats.heap_alloc;
obj0 = mstats.nmalloc - mstats.nfree;
}
m->locks++; // disable gc during mallocs in parforalloc
if(work.markfor == nil)
work.markfor = runtime_parforalloc(MaxGcproc);
if(work.sweepfor == nil)
work.sweepfor = runtime_parforalloc(MaxGcproc);
m->locks--;
if(itabtype == nil) {
// get C pointer to the Go type "itab"
// runtime_gc_itab_ptr(&eface);
// itabtype = ((PtrType*)eface.type)->elem;
}
work.nwait = 0;
work.ndone = 0;
work.debugmarkdone = 0;
work.nproc = runtime_gcprocs();
addroots();
runtime_parforsetup(work.markfor, work.nproc, work.nroot, nil, false, markroot);
runtime_parforsetup(work.sweepfor, work.nproc, runtime_mheap.nspan, nil, true, sweepspan);
if(work.nproc > 1) {
runtime_noteclear(&work.alldone);
runtime_helpgc(work.nproc);
}
t1 = runtime_nanotime();
gchelperstart();
runtime_parfordo(work.markfor);
scanblock(nil, nil, 0, true);
if(DebugMark) {
for(i=0; i<work.nroot; i++)
debug_scanblock(work.roots[i].p, work.roots[i].n);
runtime_atomicstore(&work.debugmarkdone, 1);
}
t2 = runtime_nanotime();
runtime_parfordo(work.sweepfor);
bufferList[m->helpgc].busy = 0;
t3 = runtime_nanotime();
if(work.nproc > 1)
runtime_notesleep(&work.alldone);
cachestats();
mstats.next_gc = mstats.heap_alloc+mstats.heap_alloc*gcpercent/100;
t4 = runtime_nanotime();
mstats.last_gc = t4;
mstats.pause_ns[mstats.numgc%nelem(mstats.pause_ns)] = t4 - t0;
mstats.pause_total_ns += t4 - t0;
mstats.numgc++;
if(mstats.debuggc)
runtime_printf("pause %D\n", t4-t0);
if(runtime_debug.gctrace) {
updatememstats(&stats);
heap1 = mstats.heap_alloc;
obj1 = mstats.nmalloc - mstats.nfree;
stats.nprocyield += work.sweepfor->nprocyield;
stats.nosyield += work.sweepfor->nosyield;
stats.nsleep += work.sweepfor->nsleep;
runtime_printf("gc%d(%d): %D+%D+%D ms, %D -> %D MB %D -> %D (%D-%D) objects,"
" %D(%D) handoff, %D(%D) steal, %D/%D/%D yields\n",
mstats.numgc, work.nproc, (t2-t1)/1000000, (t3-t2)/1000000, (t1-t0+t4-t3)/1000000,
heap0>>20, heap1>>20, obj0, obj1,
mstats.nmalloc, mstats.nfree,
stats.nhandoff, stats.nhandoffcnt,
work.sweepfor->nsteal, work.sweepfor->nstealcnt,
stats.nprocyield, stats.nosyield, stats.nsleep);
if(CollectStats) {
runtime_printf("scan: %D bytes, %D objects, %D untyped, %D types from MSpan\n",
gcstats.nbytes, gcstats.obj.cnt, gcstats.obj.notype, gcstats.obj.typelookup);
if(gcstats.ptr.cnt != 0)
runtime_printf("avg ptrbufsize: %D (%D/%D)\n",
gcstats.ptr.sum/gcstats.ptr.cnt, gcstats.ptr.sum, gcstats.ptr.cnt);
if(gcstats.obj.cnt != 0)
runtime_printf("avg nobj: %D (%D/%D)\n",
gcstats.obj.sum/gcstats.obj.cnt, gcstats.obj.sum, gcstats.obj.cnt);
runtime_printf("rescans: %D, %D bytes\n", gcstats.rescan, gcstats.rescanbytes);
runtime_printf("instruction counts:\n");
ninstr = 0;
for(i=0; i<nelem(gcstats.instr); i++) {
runtime_printf("\t%d:\t%D\n", i, gcstats.instr[i]);
ninstr += gcstats.instr[i];
}
runtime_printf("\ttotal:\t%D\n", ninstr);
runtime_printf("putempty: %D, getfull: %D\n", gcstats.putempty, gcstats.getfull);
runtime_printf("markonly base lookup: bit %D word %D span %D\n", gcstats.markonly.foundbit, gcstats.markonly.foundword, gcstats.markonly.foundspan);
runtime_printf("flushptrbuf base lookup: bit %D word %D span %D\n", gcstats.flushptrbuf.foundbit, gcstats.flushptrbuf.foundword, gcstats.flushptrbuf.foundspan);
}
}
runtime_MProf_GC();
}
void runtime_ReadMemStats(MStats *)
__asm__ (GOSYM_PREFIX "runtime.ReadMemStats");
void
runtime_ReadMemStats(MStats *stats)
{
M *m;
// Have to acquire worldsema to stop the world,
// because stoptheworld can only be used by
// one goroutine at a time, and there might be
// a pending garbage collection already calling it.
runtime_semacquire(&runtime_worldsema, false);
m = runtime_m();
m->gcing = 1;
runtime_stoptheworld();
updatememstats(nil);
*stats = mstats;
m->gcing = 0;
m->locks++;
runtime_semrelease(&runtime_worldsema);
runtime_starttheworld();
m->locks--;
}
void runtime_debug_readGCStats(Slice*)
__asm__("runtime_debug.readGCStats");
void
runtime_debug_readGCStats(Slice *pauses)
{
uint64 *p;
uint32 i, n;
// Calling code in runtime/debug should make the slice large enough.
if((size_t)pauses->cap < nelem(mstats.pause_ns)+3)
runtime_throw("runtime: short slice passed to readGCStats");
// Pass back: pauses, last gc (absolute time), number of gc, total pause ns.
p = (uint64*)pauses->array;
runtime_lock(&runtime_mheap);
n = mstats.numgc;
if(n > nelem(mstats.pause_ns))
n = nelem(mstats.pause_ns);
// The pause buffer is circular. The most recent pause is at
// pause_ns[(numgc-1)%nelem(pause_ns)], and then backward
// from there to go back farther in time. We deliver the times
// most recent first (in p[0]).
for(i=0; i<n; i++)
p[i] = mstats.pause_ns[(mstats.numgc-1-i)%nelem(mstats.pause_ns)];
p[n] = mstats.last_gc;
p[n+1] = mstats.numgc;
p[n+2] = mstats.pause_total_ns;
runtime_unlock(&runtime_mheap);
pauses->__count = n+3;
}
intgo runtime_debug_setGCPercent(intgo)
__asm__("runtime_debug.setGCPercent");
intgo
runtime_debug_setGCPercent(intgo in)
{
intgo out;
runtime_lock(&runtime_mheap);
if(gcpercent == GcpercentUnknown)
gcpercent = readgogc();
out = gcpercent;
if(in < 0)
in = -1;
gcpercent = in;
runtime_unlock(&runtime_mheap);
return out;
}
static void
gchelperstart(void)
{
M *m;
m = runtime_m();
if(m->helpgc < 0 || m->helpgc >= MaxGcproc)
runtime_throw("gchelperstart: bad m->helpgc");
if(runtime_xchg(&bufferList[m->helpgc].busy, 1))
runtime_throw("gchelperstart: already busy");
if(runtime_g() != m->g0)
runtime_throw("gchelper not running on g0 stack");
}
static void
runfinq(void* dummy __attribute__ ((unused)))
{
Finalizer *f;
FinBlock *fb, *next;
uint32 i;
Eface ef;
Iface iface;
for(;;) {
runtime_lock(&finlock);
fb = finq;
finq = nil;
if(fb == nil) {
fingwait = 1;
runtime_park(runtime_unlock, &finlock, "finalizer wait");
continue;
}
runtime_unlock(&finlock);
if(raceenabled)
runtime_racefingo();
for(; fb; fb=next) {
next = fb->next;
for(i=0; i<(uint32)fb->cnt; i++) {
const Type *fint;
void *param;
f = &fb->fin[i];
fint = ((const Type**)f->ft->__in.array)[0];
if(fint->kind == KindPtr) {
// direct use of pointer
param = &f->arg;
} else if(((const InterfaceType*)fint)->__methods.__count == 0) {
// convert to empty interface
ef.type = (const Type*)f->ot;
ef.__object = f->arg;
param = &ef;
} else {
// convert to interface with methods
iface.__methods = __go_convert_interface_2((const Type*)fint,
(const Type*)f->ot,
1);
iface.__object = f->arg;
if(iface.__methods == nil)
runtime_throw("invalid type conversion in runfinq");
param = &iface;
}
reflect_call(f->ft, f->fn, 0, 0, &param, nil);
f->fn = nil;
f->arg = nil;
f->ot = nil;
}
fb->cnt = 0;
fb->next = finc;
finc = fb;
}
runtime_gc(1); // trigger another gc to clean up the finalized objects, if possible
}
}
// mark the block at v of size n as allocated.
// If noscan is true, mark it as not needing scanning.
void
runtime_markallocated(void *v, uintptr n, bool noscan)
{
uintptr *b, obits, bits, off, shift;
if(0)
runtime_printf("markallocated %p+%p\n", v, n);
if((byte*)v+n > (byte*)runtime_mheap.arena_used || (byte*)v < runtime_mheap.arena_start)
runtime_throw("markallocated: bad pointer");
off = (uintptr*)v - (uintptr*)runtime_mheap.arena_start; // word offset
b = (uintptr*)runtime_mheap.arena_start - off/wordsPerBitmapWord - 1;
shift = off % wordsPerBitmapWord;
for(;;) {
obits = *b;
bits = (obits & ~(bitMask<<shift)) | (bitAllocated<<shift);
if(noscan)
bits |= bitNoScan<<shift;
if(runtime_gomaxprocs == 1) {
*b = bits;
break;
} else {
// more than one goroutine is potentially running: use atomic op
if(runtime_casp((void**)b, (void*)obits, (void*)bits))
break;
}
}
}
// mark the block at v of size n as freed.
void
runtime_markfreed(void *v, uintptr n)
{
uintptr *b, obits, bits, off, shift;
if(0)
runtime_printf("markfreed %p+%p\n", v, n);
if((byte*)v+n > (byte*)runtime_mheap.arena_used || (byte*)v < runtime_mheap.arena_start)
runtime_throw("markfreed: bad pointer");
off = (uintptr*)v - (uintptr*)runtime_mheap.arena_start; // word offset
b = (uintptr*)runtime_mheap.arena_start - off/wordsPerBitmapWord - 1;
shift = off % wordsPerBitmapWord;
for(;;) {
obits = *b;
bits = (obits & ~(bitMask<<shift)) | (bitBlockBoundary<<shift);
if(runtime_gomaxprocs == 1) {
*b = bits;
break;
} else {
// more than one goroutine is potentially running: use atomic op
if(runtime_casp((void**)b, (void*)obits, (void*)bits))
break;
}
}
}
// check that the block at v of size n is marked freed.
void
runtime_checkfreed(void *v, uintptr n)
{
uintptr *b, bits, off, shift;
if(!runtime_checking)
return;
if((byte*)v+n > (byte*)runtime_mheap.arena_used || (byte*)v < runtime_mheap.arena_start)
return; // not allocated, so okay
off = (uintptr*)v - (uintptr*)runtime_mheap.arena_start; // word offset
b = (uintptr*)runtime_mheap.arena_start - off/wordsPerBitmapWord - 1;
shift = off % wordsPerBitmapWord;
bits = *b>>shift;
if((bits & bitAllocated) != 0) {
runtime_printf("checkfreed %p+%p: off=%p have=%p\n",
v, n, off, bits & bitMask);
runtime_throw("checkfreed: not freed");
}
}
// mark the span of memory at v as having n blocks of the given size.
// if leftover is true, there is left over space at the end of the span.
void
runtime_markspan(void *v, uintptr size, uintptr n, bool leftover)
{
uintptr *b, off, shift;
byte *p;
if((byte*)v+size*n > (byte*)runtime_mheap.arena_used || (byte*)v < runtime_mheap.arena_start)
runtime_throw("markspan: bad pointer");
p = v;
if(leftover) // mark a boundary just past end of last block too
n++;
for(; n-- > 0; p += size) {
// Okay to use non-atomic ops here, because we control
// the entire span, and each bitmap word has bits for only
// one span, so no other goroutines are changing these
// bitmap words.
off = (uintptr*)p - (uintptr*)runtime_mheap.arena_start; // word offset
b = (uintptr*)runtime_mheap.arena_start - off/wordsPerBitmapWord - 1;
shift = off % wordsPerBitmapWord;
*b = (*b & ~(bitMask<<shift)) | (bitBlockBoundary<<shift);
}
}
// unmark the span of memory at v of length n bytes.
void
runtime_unmarkspan(void *v, uintptr n)
{
uintptr *p, *b, off;
if((byte*)v+n > (byte*)runtime_mheap.arena_used || (byte*)v < runtime_mheap.arena_start)
runtime_throw("markspan: bad pointer");
p = v;
off = p - (uintptr*)runtime_mheap.arena_start; // word offset
if(off % wordsPerBitmapWord != 0)
runtime_throw("markspan: unaligned pointer");
b = (uintptr*)runtime_mheap.arena_start - off/wordsPerBitmapWord - 1;
n /= PtrSize;
if(n%wordsPerBitmapWord != 0)
runtime_throw("unmarkspan: unaligned length");
// Okay to use non-atomic ops here, because we control
// the entire span, and each bitmap word has bits for only
// one span, so no other goroutines are changing these
// bitmap words.
n /= wordsPerBitmapWord;
while(n-- > 0)
*b-- = 0;
}
bool
runtime_blockspecial(void *v)
{
uintptr *b, off, shift;
if(DebugMark)
return true;
off = (uintptr*)v - (uintptr*)runtime_mheap.arena_start;
b = (uintptr*)runtime_mheap.arena_start - off/wordsPerBitmapWord - 1;
shift = off % wordsPerBitmapWord;
return (*b & (bitSpecial<<shift)) != 0;
}
void
runtime_setblockspecial(void *v, bool s)
{
uintptr *b, off, shift, bits, obits;
if(DebugMark)
return;
off = (uintptr*)v - (uintptr*)runtime_mheap.arena_start;
b = (uintptr*)runtime_mheap.arena_start - off/wordsPerBitmapWord - 1;
shift = off % wordsPerBitmapWord;
for(;;) {
obits = *b;
if(s)
bits = obits | (bitSpecial<<shift);
else
bits = obits & ~(bitSpecial<<shift);
if(runtime_gomaxprocs == 1) {
*b = bits;
break;
} else {
// more than one goroutine is potentially running: use atomic op
if(runtime_casp((void**)b, (void*)obits, (void*)bits))
break;
}
}
}
void
runtime_MHeap_MapBits(MHeap *h)
{
size_t page_size;
// Caller has added extra mappings to the arena.
// Add extra mappings of bitmap words as needed.
// We allocate extra bitmap pieces in chunks of bitmapChunk.
enum {
bitmapChunk = 8192
};
uintptr n;
n = (h->arena_used - h->arena_start) / wordsPerBitmapWord;
n = ROUND(n, bitmapChunk);
if(h->bitmap_mapped >= n)
return;
page_size = getpagesize();
n = (n+page_size-1) & ~(page_size-1);
runtime_SysMap(h->arena_start - n, n - h->bitmap_mapped, &mstats.gc_sys);
h->bitmap_mapped = n;
}