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runtime: copy Go 1.7 runtime semaphore code 

This triggered a check in releaseSudog that g.param not nil, because
    libgo uses the param field when starting a goroutine.  Fixed by clearing
    g->param in kickoff in proc.c.
    
    Reviewed-on: https://go-review.googlesource.com/30951

From-SVN: r241067
This commit is contained in:
Ian Lance Taylor 2016-10-12 15:38:56 +00:00
parent 859e95abb8
commit 543f217b7a
7 changed files with 368 additions and 478 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
gcc/go/gofrontend/MERGE
View File

@ -1,4 +1,4 @@
d56717f8c434b3d6b753c027487681769e201e14
7e4543d050339e113e6278fd442d940c0f1a5670
The first line of this file holds the git revision number of the last
merge done from the gofrontend repository.

1
libgo/Makefile.am
View File

@ -528,7 +528,6 @@ runtime_files = \
rdebug.c \
reflect.c \
runtime1.c \
sema.c \
sigqueue.c \
string.c \
time.c \

4
libgo/Makefile.in
View File

@ -265,7 +265,7 @@ am__objects_6 = go-append.lo go-assert.lo go-assert-interface.lo \
$(am__objects_2) panic.lo parfor.lo print.lo proc.lo \
runtime.lo signal_unix.lo thread.lo $(am__objects_3) yield.lo \
$(am__objects_4) cpuprof.lo go-iface.lo lfstack.lo malloc.lo \
mprof.lo netpoll.lo rdebug.lo reflect.lo runtime1.lo sema.lo \
mprof.lo netpoll.lo rdebug.lo reflect.lo runtime1.lo \
sigqueue.lo string.lo time.lo $(am__objects_5)
am_libgo_llgo_la_OBJECTS = $(am__objects_6)
libgo_llgo_la_OBJECTS = $(am_libgo_llgo_la_OBJECTS)
@ -930,7 +930,6 @@ runtime_files = \
rdebug.c \
reflect.c \
runtime1.c \
sema.c \
sigqueue.c \
string.c \
time.c \
@ -1656,7 +1655,6 @@ distclean-compile:
@AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/rtems-task-variable-add.Plo@am__quote@
@AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/runtime.Plo@am__quote@
@AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/runtime1.Plo@am__quote@
@AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/sema.Plo@am__quote@
@AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/signal_unix.Plo@am__quote@
@AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/sigqueue.Plo@am__quote@
@AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/string.Plo@am__quote@

358
libgo/go/runtime/sema.go Normal file
View File

@ -0,0 +1,358 @@
// 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.
// Semaphore implementation exposed to Go.
// Intended use is provide a sleep and wakeup
// primitive that can be used in the contended case
// of other synchronization primitives.
// Thus it targets the same goal as Linux's futex,
// but it has much simpler semantics.
//
// That is, don't think of these as semaphores.
// Think of them as a way to implement sleep and wakeup
// such that every sleep is paired with a single wakeup,
// even if, due to races, the wakeup happens before the sleep.
//
// See Mullender and Cox, ``Semaphores in Plan 9,''
// http://swtch.com/semaphore.pdf
package runtime
// Export temporarily for gccgo's C code to call:
//go:linkname semacquire runtime.semacquire
//go:linkname semrelease runtime.semrelease
import (
"runtime/internal/atomic"
"runtime/internal/sys"
"unsafe"
)
// Asynchronous semaphore for sync.Mutex.
type semaRoot struct {
lock mutex
head *sudog
tail *sudog
nwait uint32 // Number of waiters. Read w/o the lock.
}
// Prime to not correlate with any user patterns.
const semTabSize = 251
var semtable [semTabSize]struct {
root semaRoot
pad [sys.CacheLineSize - unsafe.Sizeof(semaRoot{})]byte
}
//go:linkname sync_runtime_Semacquire sync.runtime_Semacquire
func sync_runtime_Semacquire(addr *uint32) {
semacquire(addr, true)
}
//go:linkname net_runtime_Semacquire net.runtime_Semacquire
func net_runtime_Semacquire(addr *uint32) {
semacquire(addr, true)
}
//go:linkname sync_runtime_Semrelease sync.runtime_Semrelease
func sync_runtime_Semrelease(addr *uint32) {
semrelease(addr)
}
//go:linkname net_runtime_Semrelease net.runtime_Semrelease
func net_runtime_Semrelease(addr *uint32) {
semrelease(addr)
}
func readyWithTime(s *sudog, traceskip int) {
if s.releasetime != 0 {
s.releasetime = cputicks()
}
goready(s.g, traceskip)
}
// Called from runtime.
func semacquire(addr *uint32, profile bool) {
gp := getg()
if gp != gp.m.curg {
throw("semacquire not on the G stack")
}
// Easy case.
if cansemacquire(addr) {
return
}
// Harder case:
// increment waiter count
// try cansemacquire one more time, return if succeeded
// enqueue itself as a waiter
// sleep
// (waiter descriptor is dequeued by signaler)
s := acquireSudog()
root := semroot(addr)
t0 := int64(0)
s.releasetime = 0
if profile && blockprofilerate > 0 {
t0 = cputicks()
s.releasetime = -1
}
for {
lock(&root.lock)
// Add ourselves to nwait to disable "easy case" in semrelease.
atomic.Xadd(&root.nwait, 1)
// Check cansemacquire to avoid missed wakeup.
if cansemacquire(addr) {
atomic.Xadd(&root.nwait, -1)
unlock(&root.lock)
break
}
// Any semrelease after the cansemacquire knows we're waiting
// (we set nwait above), so go to sleep.
root.queue(addr, s)
goparkunlock(&root.lock, "semacquire", traceEvGoBlockSync, 4)
if cansemacquire(addr) {
break
}
}
if s.releasetime > 0 {
blockevent(s.releasetime-t0, 3)
}
releaseSudog(s)
}
func semrelease(addr *uint32) {
root := semroot(addr)
atomic.Xadd(addr, 1)
// Easy case: no waiters?
// This check must happen after the xadd, to avoid a missed wakeup
// (see loop in semacquire).
if atomic.Load(&root.nwait) == 0 {
return
}
// Harder case: search for a waiter and wake it.
lock(&root.lock)
if atomic.Load(&root.nwait) == 0 {
// The count is already consumed by another goroutine,
// so no need to wake up another goroutine.
unlock(&root.lock)
return
}
s := root.head
for ; s != nil; s = s.next {
if s.elem == unsafe.Pointer(addr) {
atomic.Xadd(&root.nwait, -1)
root.dequeue(s)
break
}
}
unlock(&root.lock)
if s != nil {
readyWithTime(s, 5)
}
}
func semroot(addr *uint32) *semaRoot {
return &semtable[(uintptr(unsafe.Pointer(addr))>>3)%semTabSize].root
}
func cansemacquire(addr *uint32) bool {
for {
v := atomic.Load(addr)
if v == 0 {
return false
}
if atomic.Cas(addr, v, v-1) {
return true
}
}
}
func (root *semaRoot) queue(addr *uint32, s *sudog) {
s.g = getg()
s.elem = unsafe.Pointer(addr)
s.next = nil
s.prev = root.tail
if root.tail != nil {
root.tail.next = s
} else {
root.head = s
}
root.tail = s
}
func (root *semaRoot) dequeue(s *sudog) {
if s.next != nil {
s.next.prev = s.prev
} else {
root.tail = s.prev
}
if s.prev != nil {
s.prev.next = s.next
} else {
root.head = s.next
}
s.elem = nil
s.next = nil
s.prev = nil
}
// notifyList is a ticket-based notification list used to implement sync.Cond.
//
// It must be kept in sync with the sync package.
type notifyList struct {
// wait is the ticket number of the next waiter. It is atomically
// incremented outside the lock.
wait uint32
// notify is the ticket number of the next waiter to be notified. It can
// be read outside the lock, but is only written to with lock held.
//
// Both wait & notify can wrap around, and such cases will be correctly
// handled as long as their "unwrapped" difference is bounded by 2^31.
// For this not to be the case, we'd need to have 2^31+ goroutines
// blocked on the same condvar, which is currently not possible.
notify uint32
// List of parked waiters.
lock mutex
head *sudog
tail *sudog
}
// less checks if a < b, considering a & b running counts that may overflow the
// 32-bit range, and that their "unwrapped" difference is always less than 2^31.
func less(a, b uint32) bool {
return int32(a-b) < 0
}
// notifyListAdd adds the caller to a notify list such that it can receive
// notifications. The caller must eventually call notifyListWait to wait for
// such a notification, passing the returned ticket number.
//go:linkname notifyListAdd sync.runtime_notifyListAdd
func notifyListAdd(l *notifyList) uint32 {
// This may be called concurrently, for example, when called from
// sync.Cond.Wait while holding a RWMutex in read mode.
return atomic.Xadd(&l.wait, 1) - 1
}
// notifyListWait waits for a notification. If one has been sent since
// notifyListAdd was called, it returns immediately. Otherwise, it blocks.
//go:linkname notifyListWait sync.runtime_notifyListWait
func notifyListWait(l *notifyList, t uint32) {
lock(&l.lock)
// Return right away if this ticket has already been notified.
if less(t, l.notify) {
unlock(&l.lock)
return
}
// Enqueue itself.
s := acquireSudog()
s.g = getg()
s.ticket = t
s.releasetime = 0
t0 := int64(0)
if blockprofilerate > 0 {
t0 = cputicks()
s.releasetime = -1
}
if l.tail == nil {
l.head = s
} else {
l.tail.next = s
}
l.tail = s
goparkunlock(&l.lock, "semacquire", traceEvGoBlockCond, 3)
if t0 != 0 {
blockevent(s.releasetime-t0, 2)
}
releaseSudog(s)
}
// notifyListNotifyAll notifies all entries in the list.
//go:linkname notifyListNotifyAll sync.runtime_notifyListNotifyAll
func notifyListNotifyAll(l *notifyList) {
// Fast-path: if there are no new waiters since the last notification
// we don't need to acquire the lock.
if atomic.Load(&l.wait) == atomic.Load(&l.notify) {
return
}
// Pull the list out into a local variable, waiters will be readied
// outside the lock.
lock(&l.lock)
s := l.head
l.head = nil
l.tail = nil
// Update the next ticket to be notified. We can set it to the current
// value of wait because any previous waiters are already in the list
// or will notice that they have already been notified when trying to
// add themselves to the list.
atomic.Store(&l.notify, atomic.Load(&l.wait))
unlock(&l.lock)
// Go through the local list and ready all waiters.
for s != nil {
next := s.next
s.next = nil
readyWithTime(s, 4)
s = next
}
}
// notifyListNotifyOne notifies one entry in the list.
//go:linkname notifyListNotifyOne sync.runtime_notifyListNotifyOne
func notifyListNotifyOne(l *notifyList) {
// Fast-path: if there are no new waiters since the last notification
// we don't need to acquire the lock at all.
if atomic.Load(&l.wait) == atomic.Load(&l.notify) {
return
}
lock(&l.lock)
// Re-check under the lock if we need to do anything.
t := l.notify
if t == atomic.Load(&l.wait) {
unlock(&l.lock)
return
}
// Update the next notify ticket number, and try to find the G that
// needs to be notified. If it hasn't made it to the list yet we won't
// find it, but it won't park itself once it sees the new notify number.
atomic.Store(&l.notify, t+1)
for p, s := (*sudog)(nil), l.head; s != nil; p, s = s, s.next {
if s.ticket == t {
n := s.next
if p != nil {
p.next = n
} else {
l.head = n
}
if n == nil {
l.tail = p
}
unlock(&l.lock)
s.next = nil
readyWithTime(s, 4)
return
}
}
unlock(&l.lock)
}
//go:linkname notifyListCheck sync.runtime_notifyListCheck
func notifyListCheck(sz uintptr) {
if sz != unsafe.Sizeof(notifyList{}) {
print("runtime: bad notifyList size - sync=", sz, " runtime=", unsafe.Sizeof(notifyList{}), "\n")
throw("bad notifyList size")
}
}

5
libgo/runtime/proc.c
View File

@ -246,12 +246,15 @@ static void
kickoff(void)
{
void (*fn)(void*);
void *param;
if(g->traceback != nil)
gtraceback(g);
fn = (void (*)(void*))(g->entry);
fn(g->param);
param = g->param;
g->param = nil;
fn(param);
runtime_goexit();
}

6
libgo/runtime/runtime.h
View File

@ -552,8 +552,10 @@ void runtime_newErrorCString(const char*, Eface*)
/*
* wrapped for go users
*/
void runtime_semacquire(uint32 volatile *, bool);
void runtime_semrelease(uint32 volatile *);
void runtime_semacquire(uint32 volatile *, bool)
__asm__ (GOSYM_PREFIX "runtime.semacquire");
void runtime_semrelease(uint32 volatile *)
__asm__ (GOSYM_PREFIX "runtime.semrelease");
int32 runtime_gomaxprocsfunc(int32 n);
void runtime_procyield(uint32)
__asm__(GOSYM_PREFIX "runtime.procyield");

470
libgo/runtime/sema.goc
View File

@ -1,470 +0,0 @@
// 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.
// Semaphore implementation exposed to Go.
// Intended use is provide a sleep and wakeup
// primitive that can be used in the contended case
// of other synchronization primitives.
// Thus it targets the same goal as Linux's futex,
// but it has much simpler semantics.
//
// That is, don't think of these as semaphores.
// Think of them as a way to implement sleep and wakeup
// such that every sleep is paired with a single wakeup,
// even if, due to races, the wakeup happens before the sleep.
//
// See Mullender and Cox, ``Semaphores in Plan 9,''
// http://swtch.com/semaphore.pdf
package sync
#include "runtime.h"
#include "arch.h"
typedef struct SemaWaiter SemaWaiter;
struct SemaWaiter
{
uint32 volatile* addr;
G* g;
int64 releasetime;
int32 nrelease; // -1 for acquire
SemaWaiter* prev;
SemaWaiter* next;
};
typedef struct SemaRoot SemaRoot;
struct SemaRoot
{
Lock;
SemaWaiter* head;
SemaWaiter* tail;
// Number of waiters. Read w/o the lock.
uint32 volatile nwait;
};
// Prime to not correlate with any user patterns.
#define SEMTABLESZ 251
struct semtable
{
SemaRoot;
uint8 pad[CacheLineSize-sizeof(SemaRoot)];
};
static struct semtable semtable[SEMTABLESZ];
static SemaRoot*
semroot(uint32 volatile *addr)
{
return &semtable[((uintptr)addr >> 3) % SEMTABLESZ];
}
static void
semqueue(SemaRoot *root, uint32 volatile *addr, SemaWaiter *s)
{
s->g = runtime_g();
s->addr = addr;
s->next = nil;
s->prev = root->tail;
if(root->tail)
root->tail->next = s;
else
root->head = s;
root->tail = s;
}
static void
semdequeue(SemaRoot *root, SemaWaiter *s)
{
if(s->next)
s->next->prev = s->prev;
else
root->tail = s->prev;
if(s->prev)
s->prev->next = s->next;
else
root->head = s->next;
s->prev = nil;
s->next = nil;
}
static int32
cansemacquire(uint32 volatile *addr)
{
uint32 v;
while((v = runtime_atomicload(addr)) > 0)
if(runtime_cas(addr, v, v-1))
return 1;
return 0;
}
static void readyWithTime(SudoG* s, int traceskip __attribute__ ((unused))) {
if (s->releasetime != 0) {
s->releasetime = runtime_cputicks();
}
runtime_ready(s->g);
}
void
runtime_semacquire(uint32 volatile *addr, bool profile)
{
SemaWaiter s; // Needs to be allocated on stack, otherwise garbage collector could deallocate it
SemaRoot *root;
int64 t0;
// Easy case.
if(cansemacquire(addr))
return;
// Harder case:
// increment waiter count
// try cansemacquire one more time, return if succeeded
// enqueue itself as a waiter
// sleep
// (waiter descriptor is dequeued by signaler)
root = semroot(addr);
t0 = 0;
s.releasetime = 0;
if(profile && runtime_blockprofilerate > 0) {
t0 = runtime_cputicks();
s.releasetime = -1;
}
for(;;) {
runtime_lock(root);
// Add ourselves to nwait to disable "easy case" in semrelease.
runtime_xadd(&root->nwait, 1);
// Check cansemacquire to avoid missed wakeup.
if(cansemacquire(addr)) {
runtime_xadd(&root->nwait, -1);
runtime_unlock(root);
return;
}
// Any semrelease after the cansemacquire knows we're waiting
// (we set nwait above), so go to sleep.
semqueue(root, addr, &s);
runtime_parkunlock(root, "semacquire");
if(cansemacquire(addr)) {
if(t0)
runtime_blockevent(s.releasetime - t0, 3);
return;
}
}
}
void
runtime_semrelease(uint32 volatile *addr)
{
SemaWaiter *s;
SemaRoot *root;
root = semroot(addr);
runtime_xadd(addr, 1);
// Easy case: no waiters?
// This check must happen after the xadd, to avoid a missed wakeup
// (see loop in semacquire).
if(runtime_atomicload(&root->nwait) == 0)
return;
// Harder case: search for a waiter and wake it.
runtime_lock(root);
if(runtime_atomicload(&root->nwait) == 0) {
// The count is already consumed by another goroutine,
// so no need to wake up another goroutine.
runtime_unlock(root);
return;
}
for(s = root->head; s; s = s->next) {
if(s->addr == addr) {
runtime_xadd(&root->nwait, -1);
semdequeue(root, s);
break;
}
}
runtime_unlock(root);
if(s) {
if(s->releasetime)
s->releasetime = runtime_cputicks();
runtime_ready(s->g);
}
}
// TODO(dvyukov): move to netpoll.goc once it's used by all OSes.
void net_runtime_Semacquire(uint32 *addr)
__asm__ (GOSYM_PREFIX "net.runtime_Semacquire");
void net_runtime_Semacquire(uint32 *addr)
{
runtime_semacquire(addr, true);
}
void net_runtime_Semrelease(uint32 *addr)
__asm__ (GOSYM_PREFIX "net.runtime_Semrelease");
void net_runtime_Semrelease(uint32 *addr)
{
runtime_semrelease(addr);
}
func runtime_Semacquire(addr *uint32) {
runtime_semacquire(addr, true);
}
func runtime_Semrelease(addr *uint32) {
runtime_semrelease(addr);
}
typedef struct SyncSema SyncSema;
struct SyncSema
{
Lock;
SemaWaiter* head;
SemaWaiter* tail;
};
func runtime_Syncsemcheck(size uintptr) {
if(size != sizeof(SyncSema)) {
runtime_printf("bad SyncSema size: sync:%D runtime:%D\n", (int64)size, (int64)sizeof(SyncSema));
runtime_throw("bad SyncSema size");
}
}
// Syncsemacquire waits for a pairing Syncsemrelease on the same semaphore s.
func runtime_Syncsemacquire(s *SyncSema) {
SemaWaiter w, *wake;
int64 t0;
w.g = runtime_g();
w.nrelease = -1;
w.next = nil;
w.releasetime = 0;
t0 = 0;
if(runtime_blockprofilerate > 0) {
t0 = runtime_cputicks();
w.releasetime = -1;
}
runtime_lock(s);
if(s->head && s->head->nrelease > 0) {
// have pending release, consume it
wake = nil;
s->head->nrelease--;
if(s->head->nrelease == 0) {
wake = s->head;
s->head = wake->next;
if(s->head == nil)
s->tail = nil;
}
runtime_unlock(s);
if(wake)
runtime_ready(wake->g);
} else {
// enqueue itself
if(s->tail == nil)
s->head = &w;
else
s->tail->next = &w;
s->tail = &w;
runtime_parkunlock(s, "semacquire");
if(t0)
runtime_blockevent(w.releasetime - t0, 2);
}
}
// Syncsemrelease waits for n pairing Syncsemacquire on the same semaphore s.
func runtime_Syncsemrelease(s *SyncSema, n uint32) {
SemaWaiter w, *wake;
w.g = runtime_g();
w.nrelease = (int32)n;
w.next = nil;
w.releasetime = 0;
runtime_lock(s);
while(w.nrelease > 0 && s->head && s->head->nrelease < 0) {
// have pending acquire, satisfy it
wake = s->head;
s->head = wake->next;
if(s->head == nil)
s->tail = nil;
if(wake->releasetime)
wake->releasetime = runtime_cputicks();
runtime_ready(wake->g);
w.nrelease--;
}
if(w.nrelease > 0) {
// enqueue itself
if(s->tail == nil)
s->head = &w;
else
s->tail->next = &w;
s->tail = &w;
runtime_parkunlock(s, "semarelease");
} else
runtime_unlock(s);
}
// notifyList is a ticket-based notification list used to implement sync.Cond.
//
// It must be kept in sync with the sync package.
typedef struct {
// wait is the ticket number of the next waiter. It is atomically
// incremented outside the lock.
uint32 wait;
// notify is the ticket number of the next waiter to be notified. It can
// be read outside the lock, but is only written to with lock held.
//
// Both wait & notify can wrap around, and such cases will be correctly
// handled as long as their "unwrapped" difference is bounded by 2^31.
// For this not to be the case, we'd need to have 2^31+ goroutines
// blocked on the same condvar, which is currently not possible.
uint32 notify;
// List of parked waiters.
Lock lock;
SudoG* head;
SudoG* tail;
} notifyList;
// less checks if a < b, considering a & b running counts that may overflow the
// 32-bit range, and that their "unwrapped" difference is always less than 2^31.
static bool less(uint32 a, uint32 b) {
return (int32)(a-b) < 0;
}
// notifyListAdd adds the caller to a notify list such that it can receive
// notifications. The caller must eventually call notifyListWait to wait for
// such a notification, passing the returned ticket number.
//go:linkname notifyListAdd sync.runtime_notifyListAdd
func runtime_notifyListAdd(l *notifyList) (r uint32) {
// This may be called concurrently, for example, when called from
// sync.Cond.Wait while holding a RWMutex in read mode.
r = runtime_xadd(&l->wait, 1) - 1;
}
// notifyListWait waits for a notification. If one has been sent since
// notifyListAdd was called, it returns immediately. Otherwise, it blocks.
//go:linkname notifyListWait sync.runtime_notifyListWait
func runtime_notifyListWait(l *notifyList, t uint32) {
SudoG s;
int64 t0;
runtime_lock(&l->lock);
// Return right away if this ticket has already been notified.
if (less(t, l->notify)) {
runtime_unlock(&l->lock);
return;
}
// Enqueue itself.
runtime_memclr(&s, sizeof(s));
s.g = runtime_g();
s.ticket = t;
s.releasetime = 0;
t0 = 0;
if (runtime_blockprofilerate > 0) {
t0 = runtime_cputicks();
s.releasetime = -1;
}
if (l->tail == nil) {
l->head = &s;
} else {
l->tail->next = &s;
}
l->tail = &s;
runtime_parkunlock(&l->lock, "semacquire");
if (t0 != 0) {
runtime_blockevent(s.releasetime-t0, 2);
}
}
// notifyListNotifyAll notifies all entries in the list.
//go:linkname notifyListNotifyAll sync.runtime_notifyListNotifyAll
func runtime_notifyListNotifyAll(l *notifyList) {
SudoG *s;
// Fast-path: if there are no new waiters since the last notification
// we don't need to acquire the lock.
if (runtime_atomicload(&l->wait) == runtime_atomicload(&l->notify)) {
return;
}
// Pull the list out into a local variable, waiters will be readied
// outside the lock.
runtime_lock(&l->lock);
s = l->head;
l->head = nil;
l->tail = nil;
// Update the next ticket to be notified. We can set it to the current
// value of wait because any previous waiters are already in the list
// or will notice that they have already been notified when trying to
// add themselves to the list.
runtime_atomicstore(&l->notify, runtime_atomicload(&l->wait));
runtime_unlock(&l->lock);
// Go through the local list and ready all waiters.
while (s != nil) {
SudoG* next = s->next;
s->next = nil;
readyWithTime(s, 4);
s = next;
}
}
// notifyListNotifyOne notifies one entry in the list.
//go:linkname notifyListNotifyOne sync.runtime_notifyListNotifyOne
func runtime_notifyListNotifyOne(l *notifyList) {
uint32 t;
SudoG *p;
SudoG *s;
// Fast-path: if there are no new waiters since the last notification
// we don't need to acquire the lock at all.
if (runtime_atomicload(&l->wait) == runtime_atomicload(&l->notify)) {
return;
}
runtime_lock(&l->lock);
// Re-check under the lock if we need to do anything.
t = l->notify;
if (t == runtime_atomicload(&l->wait)) {
runtime_unlock(&l->lock);
return;
}
// Update the next notify ticket number, and try to find the G that
// needs to be notified. If it hasn't made it to the list yet we won't
// find it, but it won't park itself once it sees the new notify number.
runtime_atomicstore(&l->notify, t+1);
for (p = nil, s = l->head; s != nil; p = s, s = s->next) {
if (s->ticket == t) {
SudoG *n = s->next;
if (p != nil) {
p->next = n;
} else {
l->head = n;
}
if (n == nil) {
l->tail = p;
}
runtime_unlock(&l->lock);
s->next = nil;
readyWithTime(s, 4);
return;
}
}
runtime_unlock(&l->lock);
}
//go:linkname notifyListCheck sync.runtime_notifyListCheck
func runtime_notifyListCheck(sz uintptr) {
if (sz != sizeof(notifyList)) {
runtime_printf("runtime: bad notifyList size\n");
runtime_throw("bad notifyList size");
}
}