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runtime: unify mutex code across OSes

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The change introduces 2 generic mutex implementations
(futex- and semaphore-based). Each OS chooses a suitable mutex
implementation and implements few callbacks (e.g. futex wait/wake).
The CL reduces code duplication, extends some optimizations available
only on Linux/Windows to other OSes and provides ground
for futher optimizations. Chan finalizers are finally eliminated.

(Linux/amd64, 8 HT cores)
benchmark                      old      new
BenchmarkChanContended         83.6     77.8 ns/op
BenchmarkChanContended-2       341      328 ns/op
BenchmarkChanContended-4       382      383 ns/op
BenchmarkChanContended-8       390      374 ns/op
BenchmarkChanContended-16      313      291 ns/op

(Darwin/amd64, 2 cores)
benchmark                      old      new
BenchmarkChanContended         159      172 ns/op
BenchmarkChanContended-2       6735     263 ns/op
BenchmarkChanContended-4       10384    255 ns/op
BenchmarkChanCreation          1174     407 ns/op
BenchmarkChanCreation-2        4007     254 ns/op
BenchmarkChanCreation-4        4029     246 ns/op

R=rsc, jsing, hectorchu
CC=golang-dev
https://golang.org/cl/5140043
This commit is contained in:
Dmitriy Vyukov 2011-11-02 16:42:01 +03:00
parent 5e4e8f49c5
commit ee24bfc058
11 changed files with 334 additions and 638 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

16
src/pkg/runtime/Makefile
View file

@ -30,8 +30,24 @@ GOFILES=\
CLEANFILES+=version.go version_*.go
OFILES_darwin=\
lock_sema.$O\
OFILES_freebsd=\
lock_futex.$O\
OFILES_linux=\
lock_futex.$O\
OFILES_openbsd=\
lock_sema.$O\
OFILES_plan9=\
lock_sema.$O\
OFILES_windows=\
callback.$O\
lock_sema.$O\
syscall.$O\
# 386-specific object files

10
src/pkg/runtime/chan.c
View file

@ -104,9 +104,6 @@ runtime·makechan_c(ChanType *t, int64 hint)
// allocate memory in one call
c = (Hchan*)runtime·mal(n + hint*elem->size);
if(runtime·destroylock)
runtime·addfinalizer(c, (void*)destroychan, 0);
c->elemsize = elem->size;
c->elemalg = &runtime·algarray[elem->alg];
c->elemalign = elem->align;
@ -128,13 +125,6 @@ reflect·makechan(ChanType *t, uint32 size, Hchan *c)
FLUSH(&c);
}
static void
destroychan(Hchan *c)
{
runtime·destroylock(&c->Lock);
}
// makechan(t *ChanType, hint int64) (hchan *chan any);
void
runtime·makechan(ChanType *t, int64 hint, Hchan *ret)

118
src/pkg/runtime/darwin/thread.c
View file

@ -17,127 +17,24 @@ unimplemented(int8 *name)
*(int32*)1231 = 1231;
}
// Thread-safe allocation of a semaphore.
// Psema points at a kernel semaphore key.
// It starts out zero, meaning no semaphore.
// Fill it in, being careful of others calling initsema
// simultaneously.
static void
initsema(uint32 *psema)
{
uint32 sema;
if(*psema != 0) // already have one
return;
sema = runtime·mach_semcreate();
if(!runtime·cas(psema, 0, sema)){
// Someone else filled it in. Use theirs.
runtime·mach_semdestroy(sema);
return;
}
}
// Blocking locks.
// Implement Locks, using semaphores.
// l->key is the number of threads who want the lock.
// In a race, one thread increments l->key from 0 to 1
// and the others increment it from >0 to >1. The thread
// who does the 0->1 increment gets the lock, and the
// others wait on the semaphore. When the 0->1 thread
// releases the lock by decrementing l->key, l->key will
// be >0, so it will increment the semaphore to wake up
// one of the others. This is the same algorithm used
// in Plan 9's user-level locks.
void
runtime·lock(Lock *l)
runtime·semasleep(void)
{
if(m->locks < 0)
runtime·throw("lock count");
m->locks++;
if(runtime·xadd(&l->key, 1) > 1) { // someone else has it; wait
// Allocate semaphore if needed.
if(l->sema == 0)
initsema(&l->sema);
runtime·mach_semacquire(l->sema);
}
runtime·mach_semacquire(m->waitsema);
}
void
runtime·unlock(Lock *l)
runtime·semawakeup(M *mp)
{
m->locks--;
if(m->locks < 0)
runtime·throw("lock count");
if(runtime·xadd(&l->key, -1) > 0) { // someone else is waiting
// Allocate semaphore if needed.
if(l->sema == 0)
initsema(&l->sema);
runtime·mach_semrelease(l->sema);
}
runtime·mach_semrelease(mp->waitsema);
}
static void
destroylock(Lock *l)
uintptr
runtime·semacreate(void)
{
if(l->sema != 0) {
runtime·mach_semdestroy(l->sema);
l->sema = 0;
}
return runtime·mach_semcreate();
}
// User-level semaphore implementation:
// try to do the operations in user space on u,
// but when it's time to block, fall back on the kernel semaphore k.
// This is the same algorithm used in Plan 9.
void
runtime·usemacquire(Usema *s)
{
if((int32)runtime·xadd(&s->u, -1) < 0) {
if(s->k == 0)
initsema(&s->k);
runtime·mach_semacquire(s->k);
}
}
void
runtime·usemrelease(Usema *s)
{
if((int32)runtime·xadd(&s->u, 1) <= 0) {
if(s->k == 0)
initsema(&s->k);
runtime·mach_semrelease(s->k);
}
}
// Event notifications.
void
runtime·noteclear(Note *n)
{
n->wakeup = 0;
}
void
runtime·notesleep(Note *n)
{
while(!n->wakeup)
runtime·usemacquire(&n->sema);
}
void
runtime·notewakeup(Note *n)
{
n->wakeup = 1;
runtime·usemrelease(&n->sema);
}
// BSD interface for threading.
void
runtime·osinit(void)
@ -147,7 +44,6 @@ runtime·osinit(void)
// to let the C pthread libary install its own thread-creation callback.
if(!runtime·iscgo)
runtime·bsdthread_register();
runtime·destroylock = destroylock;
// Use sysctl to fetch hw.ncpu.
uint32 mib[2];

95
src/pkg/runtime/freebsd/thread.c
View file

@ -12,8 +12,8 @@ extern int32 runtime·sys_umtx_op(uint32*, int32, uint32, void*, void*);
// FreeBSD's umtx_op syscall is effectively the same as Linux's futex, and
// thus the code is largely similar. See linux/thread.c for comments.
static void
umtx_wait(uint32 *addr, uint32 val)
void
runtime·futexsleep(uint32 *addr, uint32 val)
{
int32 ret;
@ -25,12 +25,12 @@ umtx_wait(uint32 *addr, uint32 val)
*(int32*)0x1005 = 0x1005;
}
static void
umtx_wake(uint32 *addr)
void
runtime·futexwakeup(uint32 *addr, uint32 cnt)
{
int32 ret;
ret = runtime·sys_umtx_op(addr, UMTX_OP_WAKE, 1, nil, nil);
ret = runtime·sys_umtx_op(addr, UMTX_OP_WAKE, cnt, nil, nil);
if(ret >= 0)
return;
@ -38,91 +38,6 @@ umtx_wake(uint32 *addr)
*(int32*)0x1006 = 0x1006;
}
// See linux/thread.c for comments about the algorithm.
static void
umtx_lock(Lock *l)
{
uint32 v;
again:
v = l->key;
if((v&1) == 0){
if(runtime·cas(&l->key, v, v|1))
return;
goto again;
}
if(!runtime·cas(&l->key, v, v+2))
goto again;
umtx_wait(&l->key, v+2);
for(;;){
v = l->key;
if(v < 2)
runtime·throw("bad lock key");
if(runtime·cas(&l->key, v, v-2))
break;
}
goto again;
}
static void
umtx_unlock(Lock *l)
{
uint32 v;
again:
v = l->key;
if((v&1) == 0)
runtime·throw("unlock of unlocked lock");
if(!runtime·cas(&l->key, v, v&~1))
goto again;
if(v&~1)
umtx_wake(&l->key);
}
void
runtime·lock(Lock *l)
{
if(m->locks < 0)
runtime·throw("lock count");
m->locks++;
umtx_lock(l);
}
void
runtime·unlock(Lock *l)
{
m->locks--;
if(m->locks < 0)
runtime·throw("lock count");
umtx_unlock(l);
}
// Event notifications.
void
runtime·noteclear(Note *n)
{
n->lock.key = 0;
umtx_lock(&n->lock);
}
void
runtime·notesleep(Note *n)
{
umtx_lock(&n->lock);
umtx_unlock(&n->lock);
}
void
runtime·notewakeup(Note *n)
{
umtx_unlock(&n->lock);
}
void runtime·thr_start(void*);
void

135
src/pkg/runtime/linux/thread.c
View file

@ -24,14 +24,6 @@ int32 runtime·read(int32, void*, int32);
enum
{
MUTEX_UNLOCKED = 0,
MUTEX_LOCKED = 1,
MUTEX_SLEEPING = 2,
ACTIVE_SPIN = 4,
ACTIVE_SPIN_CNT = 30,
PASSIVE_SPIN = 1,
FUTEX_WAIT = 0,
FUTEX_WAKE = 1,
@ -39,34 +31,23 @@ enum
EAGAIN = 11,
};
// TODO(rsc): I tried using 1<<40 here but futex woke up (-ETIMEDOUT).
// I wonder if the timespec that gets to the kernel
// actually has two 32-bit numbers in it, so that
// a 64-bit 1<<40 ends up being 0 seconds,
// 1<<8 nanoseconds.
static Timespec longtime =
{
1<<30, // 34 years
0
};
// Atomically,
// if(*addr == val) sleep
// Might be woken up spuriously; that's allowed.
static void
futexsleep(uint32 *addr, uint32 val)
void
runtime·futexsleep(uint32 *addr, uint32 val)
{
// Some Linux kernels have a bug where futex of
// FUTEX_WAIT returns an internal error code
// as an errno. Libpthread ignores the return value
// here, and so can we: as it says a few lines up,
// spurious wakeups are allowed.
runtime·futex(addr, FUTEX_WAIT, val, &longtime, nil, 0);
runtime·futex(addr, FUTEX_WAIT, val, nil, nil, 0);
}
// If any procs are sleeping on addr, wake up at most cnt.
static void
futexwakeup(uint32 *addr, uint32 cnt)
void
runtime·futexwakeup(uint32 *addr, uint32 cnt)
{
int64 ret;
@ -112,112 +93,6 @@ getproccount(void)
return cnt ? cnt : 1;
}
// Possible lock states are MUTEX_UNLOCKED, MUTEX_LOCKED and MUTEX_SLEEPING.
// MUTEX_SLEEPING means that there is presumably at least one sleeping thread.
// Note that there can be spinning threads during all states - they do not
// affect mutex's state.
static void
futexlock(Lock *l)
{
uint32 i, v, wait, spin;
// Speculative grab for lock.
v = runtime·xchg(&l->key, MUTEX_LOCKED);
if(v == MUTEX_UNLOCKED)
return;
// wait is either MUTEX_LOCKED or MUTEX_SLEEPING
// depending on whether there is a thread sleeping
// on this mutex. If we ever change l->key from
// MUTEX_SLEEPING to some other value, we must be
// careful to change it back to MUTEX_SLEEPING before
// returning, to ensure that the sleeping thread gets
// its wakeup call.
wait = v;
// On uniprocessor's, no point spinning.
// On multiprocessors, spin for ACTIVE_SPIN attempts.
spin = 0;
if(runtime·ncpu > 1)
spin = ACTIVE_SPIN;
for(;;) {
// Try for lock, spinning.
for(i = 0; i < spin; i++) {
while(l->key == MUTEX_UNLOCKED)
if(runtime·cas(&l->key, MUTEX_UNLOCKED, wait))
return;
runtime·procyield(ACTIVE_SPIN_CNT);
}
// Try for lock, rescheduling.
for(i=0; i < PASSIVE_SPIN; i++) {
while(l->key == MUTEX_UNLOCKED)
if(runtime·cas(&l->key, MUTEX_UNLOCKED, wait))
return;
runtime·osyield();
}
// Sleep.
v = runtime·xchg(&l->key, MUTEX_SLEEPING);
if(v == MUTEX_UNLOCKED)
return;
wait = MUTEX_SLEEPING;
futexsleep(&l->key, MUTEX_SLEEPING);
}
}
static void
futexunlock(Lock *l)
{
uint32 v;
v = runtime·xchg(&l->key, MUTEX_UNLOCKED);
if(v == MUTEX_UNLOCKED)
runtime·throw("unlock of unlocked lock");
if(v == MUTEX_SLEEPING)
futexwakeup(&l->key, 1);
}
void
runtime·lock(Lock *l)
{
if(m->locks++ < 0)
runtime·throw("runtime·lock: lock count");
futexlock(l);
}
void
runtime·unlock(Lock *l)
{
if(--m->locks < 0)
runtime·throw("runtime·unlock: lock count");
futexunlock(l);
}
// One-time notifications.
void
runtime·noteclear(Note *n)
{
n->state = 0;
}
void
runtime·notewakeup(Note *n)
{
runtime·xchg(&n->state, 1);
futexwakeup(&n->state, 1<<30);
}
void
runtime·notesleep(Note *n)
{
while(runtime·atomicload(&n->state) == 0)
futexsleep(&n->state, 0);
}
// Clone, the Linux rfork.
enum
{

118
src/pkg/runtime/lock_futex.c Normal file
View file

@ -0,0 +1,118 @@
// Copyright 2011 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.
#include "runtime.h"
enum
{
MUTEX_UNLOCKED = 0,
MUTEX_LOCKED = 1,
MUTEX_SLEEPING = 2,
ACTIVE_SPIN = 4,
ACTIVE_SPIN_CNT = 30,
PASSIVE_SPIN = 1,
};
// Atomically,
// if(*addr == val) sleep
// Might be woken up spuriously; that's allowed.
void runtime·futexsleep(uint32 *addr, uint32 val);
// If any procs are sleeping on addr, wake up at most cnt.
void runtime·futexwakeup(uint32 *addr, uint32 cnt);
// Possible lock states are MUTEX_UNLOCKED, MUTEX_LOCKED and MUTEX_SLEEPING.
// MUTEX_SLEEPING means that there is presumably at least one sleeping thread.
// Note that there can be spinning threads during all states - they do not
// affect mutex's state.
void
runtime·lock(Lock *l)
{
uint32 i, v, wait, spin;
if(m->locks++ < 0)
runtime·throw("runtime·lock: lock count");
// Speculative grab for lock.
v = runtime·xchg(&l->key, MUTEX_LOCKED);
if(v == MUTEX_UNLOCKED)
return;
// wait is either MUTEX_LOCKED or MUTEX_SLEEPING
// depending on whether there is a thread sleeping
// on this mutex. If we ever change l->key from
// MUTEX_SLEEPING to some other value, we must be
// careful to change it back to MUTEX_SLEEPING before
// returning, to ensure that the sleeping thread gets
// its wakeup call.
wait = v;
// On uniprocessor's, no point spinning.
// On multiprocessors, spin for ACTIVE_SPIN attempts.
spin = 0;
if(runtime·ncpu > 1)
spin = ACTIVE_SPIN;
for(;;) {
// Try for lock, spinning.
for(i = 0; i < spin; i++) {
while(l->key == MUTEX_UNLOCKED)
if(runtime·cas(&l->key, MUTEX_UNLOCKED, wait))
return;
runtime·procyield(ACTIVE_SPIN_CNT);
}
// Try for lock, rescheduling.
for(i=0; i < PASSIVE_SPIN; i++) {
while(l->key == MUTEX_UNLOCKED)
if(runtime·cas(&l->key, MUTEX_UNLOCKED, wait))
return;
runtime·osyield();
}
// Sleep.
v = runtime·xchg(&l->key, MUTEX_SLEEPING);
if(v == MUTEX_UNLOCKED)
return;
wait = MUTEX_SLEEPING;
runtime·futexsleep(&l->key, MUTEX_SLEEPING);
}
}
void
runtime·unlock(Lock *l)
{
uint32 v;
if(--m->locks < 0)
runtime·throw("runtime·unlock: lock count");
v = runtime·xchg(&l->key, MUTEX_UNLOCKED);
if(v == MUTEX_UNLOCKED)
runtime·throw("unlock of unlocked lock");
if(v == MUTEX_SLEEPING)
runtime·futexwakeup(&l->key, 1);
}
// One-time notifications.
void
runtime·noteclear(Note *n)
{
n->key = 0;
}
void
runtime·notewakeup(Note *n)
{
runtime·xchg(&n->key, 1);
runtime·futexwakeup(&n->key, 1);
}
void
runtime·notesleep(Note *n)
{
while(runtime·atomicload(&n->key) == 0)
runtime·futexsleep(&n->key, 0);
}

128
src/pkg/runtime/lock_sema.c Normal file
View file

@ -0,0 +1,128 @@
// Copyright 2011 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.
#include "runtime.h"
enum
{
LOCKED = 1,
ACTIVE_SPIN = 4,
ACTIVE_SPIN_CNT = 30,
PASSIVE_SPIN = 1,
};
// creates per-M semaphore (must not return 0)
uintptr runtime·semacreate(void);
// acquires per-M semaphore
void runtime·semasleep(void);
// releases mp's per-M semaphore
void runtime·semawakeup(M *mp);
void
runtime·lock(Lock *l)
{
uintptr v;
uint32 i, spin;
if(m->locks++ < 0)
runtime·throw("runtime·lock: lock count");
// Speculative grab for lock.
if(runtime·casp(&l->waitm, nil, (void*)LOCKED))
return;
if(m->waitsema == 0)
m->waitsema = runtime·semacreate();
// On uniprocessor's, no point spinning.
// On multiprocessors, spin for ACTIVE_SPIN attempts.
spin = 0;
if(runtime·ncpu > 1)
spin = ACTIVE_SPIN;
for(i=0;; i++) {
v = (uintptr)runtime·atomicloadp(&l->waitm);
if((v&LOCKED) == 0) {
unlocked:
if(runtime·casp(&l->waitm, (void*)v, (void*)(v|LOCKED)))
return;
i = 0;
}
if(i<spin)
runtime·procyield(ACTIVE_SPIN_CNT);
else if(i<spin+PASSIVE_SPIN)
runtime·osyield();
else {
// Someone else has it.
// l->waitm points to a linked list of M's waiting
// for this lock, chained through m->nextwaitm.
// Queue this M.
for(;;) {
m->nextwaitm = (void*)(v&~LOCKED);
if(runtime·casp(&l->waitm, (void*)v, (void*)((uintptr)m|LOCKED)))
break;
v = (uintptr)runtime·atomicloadp(&l->waitm);
if((v&LOCKED) == 0)
goto unlocked;
}
if(v&LOCKED) {
// Wait.
runtime·semasleep();
i = 0;
}
}
}
}
void
runtime·unlock(Lock *l)
{
uintptr v;
M *mp;
if(--m->locks < 0)
runtime·throw("runtime·unlock: lock count");
for(;;) {
v = (uintptr)runtime·atomicloadp(&l->waitm);
if(v == LOCKED) {
if(runtime·casp(&l->waitm, (void*)LOCKED, nil))
break;
} else {
// Other M's are waiting for the lock.
// Dequeue an M.
mp = (void*)(v&~LOCKED);
if(runtime·casp(&l->waitm, (void*)v, mp->nextwaitm)) {
// Wake that M.
runtime·semawakeup(mp);
break;
}
}
}
}
// One-time notifications.
void
runtime·noteclear(Note *n)
{
n->waitm = nil;
}
void
runtime·notewakeup(Note *n)
{
if(runtime·casp(&n->waitm, nil, (void*)LOCKED))
return;
runtime·semawakeup(n->waitm);
}
void
runtime·notesleep(Note *n)
{
if(m->waitsema == 0)
m->waitsema = runtime·semacreate();
if(runtime·casp(&n->waitm, nil, m))
runtime·semasleep();
}

135
src/pkg/runtime/openbsd/thread.c
View file

@ -50,126 +50,43 @@ getncpu(void)
return 1;
}
// Possible lock states are MUTEX_UNLOCKED, MUTEX_LOCKED and MUTEX_SLEEPING.
// MUTEX_SLEEPING means that there is potentially at least one sleeping thread.
// Note that there can be spinning threads during all states - they do not
// affect the mutex's state.
static void
lock(Lock *l)
uintptr
runtime·semacreate(void)
{
uint32 i, v, wait, spin;
int32 ret;
// Speculative grab for lock.
v = runtime·xchg(&l->key, MUTEX_LOCKED);
if(v == MUTEX_UNLOCKED)
return;
// If we ever change the lock from MUTEX_SLEEPING to some other value,
// we must be careful to change it back to MUTEX_SLEEPING before
// returning, to ensure that the sleeping thread gets its wakeup call.
wait = v;
// No point spinning unless there are multiple processors.
spin = 0;
if(runtime·ncpu > 1)
spin = ACTIVE_SPIN;
for(;;) {
// Try for lock, spinning.
for(i = 0; i < spin; i++) {
while(l->key == MUTEX_UNLOCKED)
if(runtime·cas(&l->key, MUTEX_UNLOCKED, wait))
return;
runtime·procyield(ACTIVE_SPIN_CNT);
}
// Try for lock, rescheduling.
for(i = 0; i < PASSIVE_SPIN; i++) {
while(l->key == MUTEX_UNLOCKED)
if(runtime·cas(&l->key, MUTEX_UNLOCKED, wait))
return;
runtime·osyield();
}
// Grab a lock on sema and sleep - sema will be unlocked by
// thrsleep() and we'll get woken by another thread.
// Note that thrsleep unlocks on a _spinlock_lock_t which is
// an int on amd64, so we need to be careful here.
while (!runtime·cas(&l->sema, MUTEX_UNLOCKED, MUTEX_LOCKED))
runtime·osyield();
v = runtime·xchg(&l->key, MUTEX_SLEEPING);
if(v == MUTEX_UNLOCKED) {
l->sema = MUTEX_UNLOCKED;
return;
}
wait = v;
ret = runtime·thrsleep(&l->key, 0, 0, &l->sema);
if (ret != 0) {
runtime·printf("thrsleep addr=%p sema=%d ret=%d\n",
&l->key, l->sema, ret);
l->sema = MUTEX_UNLOCKED;
}
}
return 1;
}
static void
unlock(Lock *l)
void
runtime·semasleep(void)
{
uint32 v, ret;
while (!runtime·cas(&l->sema, MUTEX_UNLOCKED, MUTEX_LOCKED))
retry:
// spin-mutex lock
while(runtime·xchg(&m->waitsemalock, 1))
runtime·osyield();
v = runtime·xchg(&l->key, MUTEX_UNLOCKED);
l->sema = MUTEX_UNLOCKED;
if(v == MUTEX_UNLOCKED)
runtime·throw("unlock of unlocked lock");
if(v == MUTEX_SLEEPING) {
ret = runtime·thrwakeup(&l->key, 0);
if (ret != 0 && ret != ESRCH) {
runtime·printf("thrwakeup addr=%p sem=%d ret=%d\n",
&l->key, l->sema, ret);
}
if(m->waitsemacount == 0) {
// the function unlocks the spinlock
runtime·thrsleep(&m->waitsemacount, 0, 0, &m->waitsemalock);
goto retry;
}
m->waitsemacount--;
// spin-mutex unlock
runtime·atomicstore(&m->waitsemalock, 0);
}
void
runtime·lock(Lock *l)
runtime·semawakeup(M *mp)
{
if(m->locks < 0)
runtime·throw("lock count");
m->locks++;
lock(l);
}
uint32 ret;
void
runtime·unlock(Lock *l)
{
m->locks--;
if(m->locks < 0)
runtime·throw("lock count");
unlock(l);
}
// Event notifications.
void
runtime·noteclear(Note *n)
{
n->lock.key = 0;
lock(&n->lock);
}
void
runtime·notesleep(Note *n)
{
lock(&n->lock);
unlock(&n->lock);
}
void
runtime·notewakeup(Note *n)
{
unlock(&n->lock);
// spin-mutex lock
while(runtime·xchg(&mp->waitsemalock, 1))
runtime·osyield();
mp->waitsemacount++;
ret = runtime·thrwakeup(&mp->waitsemacount, 1);
if(ret != 0 && ret != ESRCH)
runtime·printf("thrwakeup addr=%p sem=%d ret=%d\n", &mp->waitsemacount, mp->waitsemacount, ret);
// spin-mutex unlock
runtime·atomicstore(&mp->waitsemalock, 0);
}
// From OpenBSD's sys/param.h

83
src/pkg/runtime/plan9/thread.c
View file

@ -4,6 +4,7 @@
#include "runtime.h"
#include "os.h"
#include "arch.h"
int8 *goos = "plan9";
@ -113,88 +114,24 @@ runtime·newosproc(M *m, G *g, void *stk, void (*fn)(void))
runtime·throw("newosproc: rfork failed");
}
// Blocking locks.
// Implement Locks, using semaphores.
// l->key is the number of threads who want the lock.
// In a race, one thread increments l->key from 0 to 1
// and the others increment it from >0 to >1. The thread
// who does the 0->1 increment gets the lock, and the
// others wait on the semaphore. When the 0->1 thread
// releases the lock by decrementing l->key, l->key will
// be >0, so it will increment the semaphore to wake up
// one of the others. This is the same algorithm used
// in Plan 9's user-level locks.
uintptr
runtime·semacreate(void)
{
return 1;
}
void
runtime·lock(Lock *l)
runtime·semasleep(void)
{
if(m->locks < 0)
runtime·throw("lock count");
m->locks++;
if(runtime·xadd(&l->key, 1) == 1)
return; // changed from 0 -> 1; we hold lock
// otherwise wait in kernel
while(runtime·plan9_semacquire(&l->sema, 1) < 0) {
while(runtime·plan9_semacquire(&m->waitsemacount, 1) < 0) {
/* interrupted; try again */
}
}
void
runtime·unlock(Lock *l)
runtime·semawakeup(M *mp)
{
m->locks--;
if(m->locks < 0)
runtime·throw("lock count");
if(runtime·xadd(&l->key, -1) == 0)
return; // changed from 1 -> 0: no contention
runtime·plan9_semrelease(&l->sema, 1);
}
// User-level semaphore implementation:
// try to do the operations in user space on u,
// but when it's time to block, fall back on the kernel semaphore k.
// This is the same algorithm used in Plan 9.
void
runtime·usemacquire(Usema *s)
{
if((int32)runtime·xadd(&s->u, -1) < 0)
while(runtime·plan9_semacquire(&s->k, 1) < 0) {
/* interrupted; try again */
}
}
void
runtime·usemrelease(Usema *s)
{
if((int32)runtime·xadd(&s->u, 1) <= 0)
runtime·plan9_semrelease(&s->k, 1);
}
// Event notifications.
void
runtime·noteclear(Note *n)
{
n->wakeup = 0;
}
void
runtime·notesleep(Note *n)
{
while(!n->wakeup)
runtime·usemacquire(&n->sema);
}
void
runtime·notewakeup(Note *n)
{
n->wakeup = 1;
runtime·usemrelease(&n->sema);
runtime·plan9_semrelease(&mp->waitsemacount, 1);
}
void

39
src/pkg/runtime/runtime.h
View file

@ -47,14 +47,13 @@ typedef struct Alg Alg;
typedef struct Func Func;
typedef struct G G;
typedef struct Gobuf Gobuf;
typedef struct Lock Lock;
typedef union Lock Lock;
typedef struct M M;
typedef struct Mem Mem;
typedef union Note Note;
typedef struct Slice Slice;
typedef struct Stktop Stktop;
typedef struct String String;
typedef struct Usema Usema;
typedef struct SigTab SigTab;
typedef struct MCache MCache;
typedef struct FixAlloc FixAlloc;
@ -117,32 +116,15 @@ enum
/*
* structures
*/
struct Lock
union Lock
{
#ifdef __WINDOWS__
M* waitm; // linked list of waiting M's
#else
uint32 key;
uint32 sema; // for OS X
#endif
};
struct Usema
{
uint32 u;
uint32 k;
uint32 key; // futex-based impl
M* waitm; // linked list of waiting M's (sema-based impl)
};
union Note
{
struct { // Linux
uint32 state;
};
struct { // Windows
Lock lock;
};
struct { // OS X
int32 wakeup;
Usema sema;
};
uint32 key; // futex-based impl
M* waitm; // waiting M (sema-based impl)
};
struct String
{
@ -253,11 +235,13 @@ struct M
uint32 freglo[16]; // D[i] lsb and F[i]
uint32 freghi[16]; // D[i] msb and F[i+16]
uint32 fflag; // floating point compare flags
M* nextwaitm; // next M waiting for lock
uintptr waitsema; // semaphore for parking on locks
uint32 waitsemacount;
uint32 waitsemalock;
#ifdef __WINDOWS__
void* thread; // thread handle
void* event; // event for signalling
M* nextwaitm; // next M waiting for lock
#endif
uintptr end[];
};
@ -409,7 +393,6 @@ extern int32 runtime·gcwaiting; // gc is waiting to run
int8* runtime·goos;
int32 runtime·ncpu;
extern bool runtime·iscgo;
extern void (*runtime·destroylock)(Lock*);
/*
* common functions and data

95
src/pkg/runtime/windows/thread.c
View file

@ -155,101 +155,22 @@ runtime·usleep(uint32 us)
runtime·stdcall(runtime·Sleep, 1, (uintptr)us);
}
// Thread-safe allocation of an event.
static void
initevent(void **pevent)
void
runtime·semasleep(void)
{
void *event;
event = runtime·stdcall(runtime·CreateEvent, 4, (uintptr)0, (uintptr)0, (uintptr)0, (uintptr)0);
if(!runtime·casp(pevent, 0, event)) {
// Someone else filled it in. Use theirs.
runtime·stdcall(runtime·CloseHandle, 1, event);
}
}
#define LOCK_HELD ((M*)-1)
static void
eventlock(Lock *l)
{
// Allocate event if needed.
if(m->event == nil)
initevent(&m->event);
for(;;) {
m->nextwaitm = runtime·atomicloadp(&l->waitm);
if(m->nextwaitm == nil) {
if(runtime·casp(&l->waitm, nil, LOCK_HELD))
return;
// Someone else has it.
// l->waitm points to a linked list of M's waiting
// for this lock, chained through m->nextwaitm.
// Queue this M.
} else if(runtime·casp(&l->waitm, m->nextwaitm, m))
break;
}
// Wait.
runtime·stdcall(runtime·WaitForSingleObject, 2, m->event, (uintptr)-1);
}
static void
eventunlock(Lock *l)
{
M *mp;
for(;;) {
mp = runtime·atomicloadp(&l->waitm);
if(mp == LOCK_HELD) {
if(runtime·casp(&l->waitm, LOCK_HELD, nil))
return;
// Other M's are waiting for the lock.
// Dequeue a M.
} else if(runtime·casp(&l->waitm, mp, mp->nextwaitm))
break;
}
// Wake that M.
runtime·stdcall(runtime·SetEvent, 1, mp->event);
runtime·stdcall(runtime·WaitForSingleObject, 2, m->waitsema, (uintptr)-1);
}
void
runtime·lock(Lock *l)
runtime·semawakeup(M *mp)
{
if(m->locks < 0)
runtime·throw("lock count");
m->locks++;
eventlock(l);
runtime·stdcall(runtime·SetEvent, 1, mp->waitsema);
}
void
runtime·unlock(Lock *l)
uintptr
runtime·semacreate(void)
{
m->locks--;
if(m->locks < 0)
runtime·throw("lock count");
eventunlock(l);
}
void
runtime·noteclear(Note *n)
{
n->lock.waitm = nil;
eventlock(&n->lock);
}
void
runtime·notewakeup(Note *n)
{
eventunlock(&n->lock);
}
void
runtime·notesleep(Note *n)
{
eventlock(&n->lock);
eventunlock(&n->lock); // Let other sleepers find out too.
return (uintptr)runtime·stdcall(runtime·CreateEvent, 4, (uintptr)0, (uintptr)0, (uintptr)0, (uintptr)0);
}
void