gcc/libgo/runtime/malloc.goc

// 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.

// See malloc.h for overview.
//
// TODO(rsc): double-check stats.

package runtime
#include <stddef.h>
#include <errno.h>
#include <stdlib.h>
#include "go-alloc.h"
#include "runtime.h"
#include "malloc.h"
#include "go-string.h"
#include "interface.h"
#include "go-type.h"
typedef struct __go_empty_interface Eface;
typedef struct __go_type_descriptor Type;
typedef struct __go_func_type FuncType;

MHeap runtime_mheap;
extern MStats mstats;	// defined in extern.go

extern volatile int32 runtime_MemProfileRate
  __asm__ ("libgo_runtime.runtime.MemProfileRate");

// Same algorithm from chan.c, but a different
// instance of the static uint32 x.
// Not protected by a lock - let the threads use
// the same random number if they like.
static uint32
fastrand1(void)
{
	static uint32 x = 0x49f6428aUL;

	x += x;
	if(x & 0x80000000L)
		x ^= 0x88888eefUL;
	return x;
}

// Allocate an object of at least size bytes.
// Small objects are allocated from the per-thread cache's free lists.
// Large objects (> 32 kB) are allocated straight from the heap.
void*
runtime_mallocgc(uintptr size, uint32 flag, int32 dogc, int32 zeroed)
{
	int32 sizeclass, rate;
	MCache *c;
	uintptr npages;
	MSpan *s;
	void *v;

	if(!__sync_bool_compare_and_swap(&m->mallocing, 0, 1))
		runtime_throw("malloc/free - deadlock");
	if(size == 0)
		size = 1;

	mstats.nmalloc++;
	if(size <= MaxSmallSize) {
		// Allocate from mcache free lists.
		sizeclass = runtime_SizeToClass(size);
		size = runtime_class_to_size[sizeclass];
		c = m->mcache;
		v = runtime_MCache_Alloc(c, sizeclass, size, zeroed);
		if(v == nil)
			runtime_throw("out of memory");
		mstats.alloc += size;
		mstats.total_alloc += size;
		mstats.by_size[sizeclass].nmalloc++;
	} else {
		// TODO(rsc): Report tracebacks for very large allocations.

		// Allocate directly from heap.
		npages = size >> PageShift;
		if((size & PageMask) != 0)
			npages++;
		s = runtime_MHeap_Alloc(&runtime_mheap, npages, 0, 1);
		if(s == nil)
			runtime_throw("out of memory");
		size = npages<<PageShift;
		mstats.alloc += size;
		mstats.total_alloc += size;
		v = (void*)(s->start << PageShift);

		// setup for mark sweep
		runtime_markspan(v, 0, 0, true);
	}
	if(!(flag & FlagNoGC))
		runtime_markallocated(v, size, (flag&FlagNoPointers) != 0);

	__sync_bool_compare_and_swap(&m->mallocing, 1, 0);

	if(__sync_bool_compare_and_swap(&m->gcing, 1, 0)) {
		if(!(flag & FlagNoProfiling))
			__go_run_goroutine_gc(0);
		else {
			// We are being called from the profiler.  Tell it
			// to invoke the garbage collector when it is
			// done.  No need to use a sync function here.
			m->gcing_for_prof = 1;
		}
	}

	if(!(flag & FlagNoProfiling) && (rate = runtime_MemProfileRate) > 0) {
		if(size >= (uint32) rate)
			goto profile;
		if((uint32) m->mcache->next_sample > size)
			m->mcache->next_sample -= size;
		else {
			// pick next profile time
			if(rate > 0x3fffffff)	// make 2*rate not overflow
				rate = 0x3fffffff;
			m->mcache->next_sample = fastrand1() % (2*rate);
		profile:
			runtime_setblockspecial(v);
			runtime_MProf_Malloc(v, size);
		}
	}

	if(dogc && mstats.heap_alloc >= mstats.next_gc)
		runtime_gc(0);
	return v;
}

void*
__go_alloc(uintptr size)
{
	return runtime_mallocgc(size, 0, 0, 1);
}

// Free the object whose base pointer is v.
void
__go_free(void *v)
{
	int32 sizeclass;
	MSpan *s;
	MCache *c;
	uint32 prof;
	uintptr size;

	if(v == nil)
		return;
	
	// If you change this also change mgc0.c:/^sweepspan,
	// which has a copy of the guts of free.

	if(!__sync_bool_compare_and_swap(&m->mallocing, 0, 1))
		runtime_throw("malloc/free - deadlock");

	if(!runtime_mlookup(v, nil, nil, &s)) {
		// runtime_printf("free %p: not an allocated block\n", v);
		runtime_throw("free runtime_mlookup");
	}
	prof = runtime_blockspecial(v);

	// Find size class for v.
	sizeclass = s->sizeclass;
	if(sizeclass == 0) {
		// Large object.
		size = s->npages<<PageShift;
		*(uintptr*)(s->start<<PageShift) = 1;	// mark as "needs to be zeroed"
		// Must mark v freed before calling unmarkspan and MHeap_Free:
		// they might coalesce v into other spans and change the bitmap further.
		runtime_markfreed(v, size);
		runtime_unmarkspan(v, 1<<PageShift);
		runtime_MHeap_Free(&runtime_mheap, s, 1);
	} else {
		// Small object.
		c = m->mcache;
		size = runtime_class_to_size[sizeclass];
		if(size > (int32)sizeof(uintptr))
			((uintptr*)v)[1] = 1;	// mark as "needs to be zeroed"
		// Must mark v freed before calling MCache_Free:
		// it might coalesce v and other blocks into a bigger span
		// and change the bitmap further.
		runtime_markfreed(v, size);
		mstats.by_size[sizeclass].nfree++;
		runtime_MCache_Free(c, v, sizeclass, size);
	}
	mstats.alloc -= size;
	if(prof)
		runtime_MProf_Free(v, size);

	__sync_bool_compare_and_swap(&m->mallocing, 1, 0);

	if(__sync_bool_compare_and_swap(&m->gcing, 1, 0))
		__go_run_goroutine_gc(1);
}

int32
runtime_mlookup(void *v, byte **base, uintptr *size, MSpan **sp)
{
	uintptr n, i;
	byte *p;
	MSpan *s;

	mstats.nlookup++;
	s = runtime_MHeap_LookupMaybe(&runtime_mheap, v);
	if(sp)
		*sp = s;
	if(s == nil) {
		runtime_checkfreed(v, 1);
		if(base)
			*base = nil;
		if(size)
			*size = 0;
		return 0;
	}

	p = (byte*)((uintptr)s->start<<PageShift);
	if(s->sizeclass == 0) {
		// Large object.
		if(base)
			*base = p;
		if(size)
			*size = s->npages<<PageShift;
		return 1;
	}

	if((byte*)v >= (byte*)s->limit) {
		// pointers past the last block do not count as pointers.
		return 0;
	}

	n = runtime_class_to_size[s->sizeclass];
	i = ((byte*)v - p)/n;
	if(base)
		*base = p + i*n;
	if(size)
		*size = n;

	return 1;
}

MCache*
runtime_allocmcache(void)
{
	MCache *c;

	if(!__sync_bool_compare_and_swap(&m->mallocing, 0, 1))
		runtime_throw("allocmcache - deadlock");

	runtime_lock(&runtime_mheap);
	c = runtime_FixAlloc_Alloc(&runtime_mheap.cachealloc);

	// Clear the free list used by FixAlloc; assume the rest is zeroed.
	c->list[0].list = nil;

	mstats.mcache_inuse = runtime_mheap.cachealloc.inuse;
	mstats.mcache_sys = runtime_mheap.cachealloc.sys;
	runtime_unlock(&runtime_mheap);

	__sync_bool_compare_and_swap(&m->mallocing, 1, 0);
	if(__sync_bool_compare_and_swap(&m->gcing, 1, 0))
		__go_run_goroutine_gc(2);

	return c;
}

extern int32 runtime_sizeof_C_MStats
  __asm__ ("libgo_runtime.runtime.Sizeof_C_MStats");

#define MaxArena32 (2U<<30)

void
runtime_mallocinit(void)
{
	byte *p;
	uintptr arena_size, bitmap_size;
	extern byte end[];

	runtime_sizeof_C_MStats = sizeof(MStats);

	runtime_InitSizes();

	// Set up the allocation arena, a contiguous area of memory where
	// allocated data will be found.  The arena begins with a bitmap large
	// enough to hold 4 bits per allocated word.
	if(sizeof(void*) == 8) {
		// On a 64-bit machine, allocate from a single contiguous reservation.
		// 16 GB should be big enough for now.
		//
		// The code will work with the reservation at any address, but ask
		// SysReserve to use 0x000000f800000000 if possible.
		// Allocating a 16 GB region takes away 36 bits, and the amd64
		// doesn't let us choose the top 17 bits, so that leaves the 11 bits
		// in the middle of 0x00f8 for us to choose.  Choosing 0x00f8 means
		// that the valid memory addresses will begin 0x00f8, 0x00f9, 0x00fa, 0x00fb.
		// None of the bytes f8 f9 fa fb can appear in valid UTF-8, and
		// they are otherwise as far from ff (likely a common byte) as possible.
		// Choosing 0x00 for the leading 6 bits was more arbitrary, but it
		// is not a common ASCII code point either.  Using 0x11f8 instead
		// caused out of memory errors on OS X during thread allocations.
		// These choices are both for debuggability and to reduce the
		// odds of the conservative garbage collector not collecting memory
		// because some non-pointer block of memory had a bit pattern
		// that matched a memory address.
		//
		// Actually we reserve 17 GB (because the bitmap ends up being 1 GB)
		// but it hardly matters: fc is not valid UTF-8 either, and we have to
		// allocate 15 GB before we get that far.
		arena_size = (uintptr)(16LL<<30);
		bitmap_size = arena_size / (sizeof(void*)*8/4);
		p = runtime_SysReserve((void*)(0x00f8ULL<<32), bitmap_size + arena_size);
		if(p == nil)
			runtime_throw("runtime: cannot reserve arena virtual address space");
	} else {
		// On a 32-bit machine, we can't typically get away
		// with a giant virtual address space reservation.
		// Instead we map the memory information bitmap
		// immediately after the data segment, large enough
		// to handle another 2GB of mappings (256 MB),
		// along with a reservation for another 512 MB of memory.
		// When that gets used up, we'll start asking the kernel
		// for any memory anywhere and hope it's in the 2GB
		// following the bitmap (presumably the executable begins
		// near the bottom of memory, so we'll have to use up
		// most of memory before the kernel resorts to giving out
		// memory before the beginning of the text segment).
		//
		// Alternatively we could reserve 512 MB bitmap, enough
		// for 4GB of mappings, and then accept any memory the
		// kernel threw at us, but normally that's a waste of 512 MB
		// of address space, which is probably too much in a 32-bit world.
		bitmap_size = MaxArena32 / (sizeof(void*)*8/4);
		arena_size = 512<<20;
		
		// SysReserve treats the address we ask for, end, as a hint,
		// not as an absolute requirement.  If we ask for the end
		// of the data segment but the operating system requires
		// a little more space before we can start allocating, it will
		// give out a slightly higher pointer.  That's fine.  
		// Run with what we get back.
		p = runtime_SysReserve(end, bitmap_size + arena_size);
		if(p == nil)
			runtime_throw("runtime: cannot reserve arena virtual address space");
	}
	if((uintptr)p & (((uintptr)1<<PageShift)-1))
		runtime_throw("runtime: SysReserve returned unaligned address");

	runtime_mheap.bitmap = p;
	runtime_mheap.arena_start = p + bitmap_size;
	runtime_mheap.arena_used = runtime_mheap.arena_start;
	runtime_mheap.arena_end = runtime_mheap.arena_start + arena_size;

	// Initialize the rest of the allocator.	
	runtime_MHeap_Init(&runtime_mheap, runtime_SysAlloc);
	m->mcache = runtime_allocmcache();

	// Initialize malloc profiling.
	runtime_Mprof_Init();

	// Initialize finalizer.
	runtime_initfintab();

	// See if it works.
	runtime_free(runtime_malloc(1));
}

void*
runtime_MHeap_SysAlloc(MHeap *h, uintptr n)
{
	byte *p;

	if(n <= (uintptr)(h->arena_end - h->arena_used)) {
		// Keep taking from our reservation.
		p = h->arena_used;
		runtime_SysMap(p, n);
		h->arena_used += n;
		runtime_MHeap_MapBits(h);
		return p;
	}
	
	// On 64-bit, our reservation is all we have.
	if(sizeof(void*) == 8)
		return nil;

	// On 32-bit, once the reservation is gone we can
	// try to get memory at a location chosen by the OS
	// and hope that it is in the range we allocated bitmap for.
	p = runtime_SysAlloc(n);
	if(p == nil)
		return nil;

	if(p < h->arena_start || (uintptr)(p+n - h->arena_start) >= MaxArena32) {
		runtime_printf("runtime: memory allocated by OS not in usable range\n");
		runtime_SysFree(p, n);
		return nil;
	}

	if(p+n > h->arena_used) {
		h->arena_used = p+n;
		if(h->arena_used > h->arena_end)
			h->arena_end = h->arena_used;
		runtime_MHeap_MapBits(h);
	}
	
	return p;
}

// Runtime stubs.

void*
runtime_mal(uintptr n)
{
	return runtime_mallocgc(n, 0, 1, 1);
}

func new(n uint32) (ret *uint8) {
	ret = runtime_mal(n);
}

func Alloc(n uintptr) (p *byte) {
	p = runtime_malloc(n);
}

func Free(p *byte) {
	runtime_free(p);
}

func Lookup(p *byte) (base *byte, size uintptr) {
	runtime_mlookup(p, &base, &size, nil);
}

func GC() {
	runtime_gc(1);
}

func SetFinalizer(obj Eface, finalizer Eface) {
	byte *base;
	uintptr size;
	const FuncType *ft;

	if(obj.__type_descriptor == nil) {
		// runtime_printf("runtime.SetFinalizer: first argument is nil interface\n");
	throw:
		runtime_throw("runtime.SetFinalizer");
	}
	if(obj.__type_descriptor->__code != GO_PTR) {
		// runtime_printf("runtime.SetFinalizer: first argument is %S, not pointer\n", *obj.type->string);
		goto throw;
	}
	if(!runtime_mlookup(obj.__object, &base, &size, nil) || obj.__object != base) {
		// runtime_printf("runtime.SetFinalizer: pointer not at beginning of allocated block\n");
		goto throw;
	}
	ft = nil;
	if(finalizer.__type_descriptor != nil) {
		if(finalizer.__type_descriptor->__code != GO_FUNC) {
		badfunc:
			// runtime_printf("runtime.SetFinalizer: second argument is %S, not func(%S)\n", *finalizer.type->string, *obj.type->string);
			goto throw;
		}
		ft = (const FuncType*)finalizer.__type_descriptor;
		if(ft->__dotdotdot || ft->__in.__count != 1 || !__go_type_descriptors_equal(*(Type**)ft->__in.__values, obj.__type_descriptor))
			goto badfunc;

		if(runtime_getfinalizer(obj.__object, 0)) {
			// runtime_printf("runtime.SetFinalizer: finalizer already set");
			goto throw;
		}
	}
	runtime_addfinalizer(obj.__object, finalizer.__type_descriptor != nil ? *(void**)finalizer.__object : nil, ft);
}