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bug 538275 - ClaimTitle cleanup. r=brendan, jorendorff

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This commit is contained in:
Igor Bukanov 2010-01-24 14:15:38 +03:00
parent b41eed1718
commit 450cf95e35
6 changed files with 137 additions and 164 deletions
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38
js/src/jscntxt.cpp
View File

@ -910,44 +910,6 @@ js_WaitForGC(JSRuntime *rt)
}
}
uint32
js_DiscountRequestsForGC(JSContext *cx)
{
uint32 requestDebit;
JS_ASSERT(cx->thread);
JS_ASSERT(cx->runtime->gcThread != cx->thread);
#ifdef JS_TRACER
if (JS_ON_TRACE(cx)) {
JS_UNLOCK_GC(cx->runtime);
LeaveTrace(cx);
JS_LOCK_GC(cx->runtime);
}
#endif
requestDebit = js_CountThreadRequests(cx);
if (requestDebit != 0) {
JSRuntime *rt = cx->runtime;
JS_ASSERT(requestDebit <= rt->requestCount);
rt->requestCount -= requestDebit;
if (rt->requestCount == 0)
JS_NOTIFY_REQUEST_DONE(rt);
}
return requestDebit;
}
void
js_RecountRequestsAfterGC(JSRuntime *rt, uint32 requestDebit)
{
while (rt->gcLevel > 0) {
JS_ASSERT(rt->gcThread);
JS_AWAIT_GC_DONE(rt);
}
if (requestDebit != 0)
rt->requestCount += requestDebit;
}
#endif
static JSDHashNumber

29
js/src/jscntxt.h
View File

@ -463,6 +463,15 @@ struct JSThread {
*/
ptrdiff_t gcThreadMallocBytes;
/*
* This thread is inside js_GC, either waiting until it can start GC, or
* waiting for GC to finish on another thread. This thread holds no locks;
* other threads may steal titles from it.
*
* Protected by rt->gcLock.
*/
bool gcWaiting;
/*
* Deallocator task for this thread.
*/
@ -1715,7 +1724,7 @@ js_NextActiveContext(JSRuntime *, JSContext *);
/*
* Count the number of contexts entered requests on the current thread.
*/
uint32
extern uint32
js_CountThreadRequests(JSContext *cx);
/*
@ -1727,24 +1736,6 @@ js_CountThreadRequests(JSContext *cx);
extern void
js_WaitForGC(JSRuntime *rt);
/*
* If we're in one or more requests (possibly on more than one context)
* running on the current thread, indicate, temporarily, that all these
* requests are inactive so a possible GC can proceed on another thread.
* This function returns the number of discounted requests. The number must
* be passed later to js_ActivateRequestAfterGC to reactivate the requests.
*
* This function must be called with the GC lock held.
*/
uint32
js_DiscountRequestsForGC(JSContext *cx);
/*
* This function must be called with the GC lock held.
*/
void
js_RecountRequestsAfterGC(JSRuntime *rt, uint32 requestDebit);
#else /* !JS_THREADSAFE */
# define js_WaitForGC(rt) ((void) 0)

71
js/src/jsgc.cpp
View File

@ -2863,7 +2863,7 @@ js_GC(JSContext *cx, JSGCInvocationKind gckind)
JSTracer trc;
JSGCArena *emptyArenas, *a, **ap;
#ifdef JS_THREADSAFE
uint32 requestDebit;
size_t requestDebit;
#endif
#ifdef JS_GCMETER
uint32 nlivearenas, nkilledarenas, nthings;
@ -2951,12 +2951,51 @@ js_GC(JSContext *cx, JSGCInvocationKind gckind)
METER_UPDATE_MAX(rt->gcStats.maxlevel, rt->gcLevel);
/*
* If the GC runs on another thread, temporarily suspend the current
* request and wait until the GC is done.
* If the GC runs on another thread, temporarily suspend all requests
* running on the current thread and wait until the GC is done.
*/
if (rt->gcThread != cx->thread) {
requestDebit = js_DiscountRequestsForGC(cx);
js_RecountRequestsAfterGC(rt, requestDebit);
requestDebit = js_CountThreadRequests(cx);
JS_ASSERT(requestDebit <= rt->requestCount);
#ifdef JS_TRACER
JS_ASSERT_IF(requestDebit == 0, !JS_ON_TRACE(cx));
#endif
if (requestDebit != 0) {
#ifdef JS_TRACER
if (JS_ON_TRACE(cx)) {
/*
* Leave trace before we decrease rt->requestCount and
* notify the GC. Otherwise the GC may start immediately
* after we unlock while this thread is still on trace.
*/
JS_UNLOCK_GC(rt);
LeaveTrace(cx);
JS_LOCK_GC(rt);
}
#endif
rt->requestCount -= requestDebit;
if (rt->requestCount == 0)
JS_NOTIFY_REQUEST_DONE(rt);
/*
* See comments before another call to js_ShareWaitingTitles
* below.
*/
cx->thread->gcWaiting = true;
js_ShareWaitingTitles(cx);
/*
* Check that we did not release the GC lock above and let the
* GC to finish before we wait.
*/
JS_ASSERT(rt->gcLevel > 0);
do {
JS_AWAIT_GC_DONE(rt);
} while (rt->gcLevel > 0);
cx->thread->gcWaiting = false;
rt->requestCount += requestDebit;
}
}
if (!(gckind & GC_LOCK_HELD))
JS_UNLOCK_GC(rt);
@ -2983,10 +3022,24 @@ js_GC(JSContext *cx, JSGCInvocationKind gckind)
*/
requestDebit = js_CountThreadRequests(cx);
JS_ASSERT_IF(cx->requestDepth != 0, requestDebit >= 1);
rt->requestCount -= requestDebit;
while (rt->requestCount > 0)
JS_AWAIT_REQUEST_DONE(rt);
rt->requestCount += requestDebit;
JS_ASSERT(requestDebit <= rt->requestCount);
if (requestDebit != rt->requestCount) {
rt->requestCount -= requestDebit;
/*
* Share any title that is owned by the GC thread before we wait, to
* avoid a deadlock with ClaimTitle. We also set the gcWaiting flag so
* that ClaimTitle can claim the title ownership from the GC thread if
* that function is called while the GC is waiting.
*/
cx->thread->gcWaiting = true;
js_ShareWaitingTitles(cx);
do {
JS_AWAIT_REQUEST_DONE(rt);
} while (rt->requestCount > 0);
cx->thread->gcWaiting = false;
rt->requestCount += requestDebit;
}
#else /* !JS_THREADSAFE */

119
js/src/jslock.cpp
View File

@ -520,16 +520,18 @@ js_NudgeOtherContexts(JSContext *cx)
* specific thread.
*/
static void
NudgeThread(JSThread *thread)
NudgeThread(JSRuntime *rt, JSThread *thread)
{
JSCList *link;
JSContext *acx;
JS_ASSERT(thread);
link = &thread->contextList;
while ((link = link->next) != &thread->contextList) {
acx = CX_FROM_THREAD_LINKS(link);
JS_ASSERT(acx->thread == thread);
if (acx->requestDepth)
/*
* We cannot walk here over thread->contextList as that is manipulated
* outside the GC lock and must be accessed only from the the thread that
* owns JSThread.
*/
JSContext *acx = NULL;
while ((acx = js_NextActiveContext(rt, acx)) != NULL) {
if (acx->thread == thread)
JS_TriggerOperationCallback(acx);
}
}
@ -545,48 +547,45 @@ NudgeThread(JSThread *thread)
static JSBool
ClaimTitle(JSTitle *title, JSContext *cx)
{
JSRuntime *rt;
JSContext *ownercx;
uint32 requestDebit;
JSRuntime *rt = cx->runtime;
JS_ASSERT_IF(cx->requestDepth == 0,
cx->thread == rt->gcThread && rt->gcRunning);
rt = cx->runtime;
JS_RUNTIME_METER(rt, claimAttempts);
JS_LOCK_GC(rt);
/* Reload in case ownercx went away while we blocked on the lock. */
while ((ownercx = title->ownercx) != NULL) {
while (JSContext *ownercx = title->ownercx) {
/*
* Avoid selflock if ownercx is dead, or is not running a request, or
* has the same thread as cx. Set title->ownercx to cx so that the
* matching JS_UNLOCK_SCOPE or JS_UNLOCK_OBJ macro call will take the
* fast path around the corresponding js_UnlockTitle or js_UnlockObj
* function call.
* has the same thread as cx, or cx->thread runs the GC (in which case
* all other requests must be suspended), or ownercx->thread runs a GC
* and the GC waits for all requests to finish. Set title->ownercx to
* cx so that the matching JS_UNLOCK_SCOPE or JS_UNLOCK_OBJ macro call
* will take the fast path around the corresponding js_UnlockTitle or
* js_UnlockObj function call.
*
* If title->u.link is non-null, title has already been inserted on
* the rt->titleSharingTodo list, because another thread's context
* already wanted to lock title while ownercx was running a request.
* That context must still be in request and cannot be dead. We can
* claim it if its thread matches ours but only if cx itself is in a
* request.
*
* The latter check covers the case when the embedding triggers a call
* to js_GC on a cx outside a request while having ownercx running a
* request on the same thread, and then js_GC calls a mark hook or a
* finalizer accessing the title. In this case we cannot claim the
* title but must share it now as no title-sharing JS_EndRequest will
* follow.
* That context must still be in request and cannot be dead. Moreover,
* the GC can not run at this moment as it must wait until all the
* titles are shared and the threads that want to lock them finish
* their requests. Thus we can claim the title if its thread matches
* ours.
*/
bool canClaim;
if (title->u.link) {
JS_ASSERT(js_ValidContextPointer(rt, ownercx));
JS_ASSERT(ownercx->requestDepth > 0);
JS_ASSERT_IF(cx->requestDepth == 0, cx->thread == rt->gcThread);
canClaim = (ownercx->thread == cx->thread &&
cx->requestDepth > 0);
JS_ASSERT(!rt->gcRunning);
canClaim = (ownercx->thread == cx->thread);
} else {
canClaim = (!js_ValidContextPointer(rt, ownercx) ||
!ownercx->requestDepth ||
ownercx->thread == cx->thread);
cx->thread == ownercx->thread ||
cx->thread == rt->gcThread ||
ownercx->thread->gcWaiting);
}
if (canClaim) {
title->ownercx = cx;
@ -607,14 +606,8 @@ ClaimTitle(JSTitle *title, JSContext *cx)
* so that control would unwind properly once these locks became
* "thin" or "fat". The engine promotes a title from exclusive to
* shared access only when locking, never when holding or unlocking.
*
* Avoid deadlock before any of this title/context cycle detection if
* cx is on the active GC's thread, because in that case, no requests
* will run until the GC completes. Any title wanted by the GC (from
* a finalizer or a mark hook) that can't be claimed must become
* shared.
*/
if (rt->gcThread == cx->thread || WillDeadlock(ownercx, cx->thread)) {
if (WillDeadlock(ownercx, cx->thread)) {
ShareTitle(cx, title);
break;
}
@ -625,26 +618,10 @@ ClaimTitle(JSTitle *title, JSContext *cx)
* non-null test, and avoid double-insertion bugs.
*/
if (!title->u.link) {
TITLE_TO_SCOPE(title)->hold();
title->u.link = rt->titleSharingTodo;
rt->titleSharingTodo = title;
}
/*
* Discount all the requests running on the current thread so a
* possible GC can proceed on another thread while we wait on
* rt->titleSharingDone.
*/
requestDebit = js_DiscountRequestsForGC(cx);
if (title->ownercx != ownercx) {
/*
* js_DiscountRequestsForGC released and reacquired the GC lock,
* and the title was taken or shared. Start over.
*/
js_RecountRequestsAfterGC(rt, requestDebit);
continue;
}
/*
* We know that some other thread's context owns title, which is now
* linked onto rt->titleSharingTodo, awaiting the end of that other
@ -652,7 +629,7 @@ ClaimTitle(JSTitle *title, JSContext *cx)
* But before waiting, we force the operation callback for that other
* thread so it can quickly suspend.
*/
NudgeThread(ownercx->thread);
NudgeThread(rt, ownercx->thread);
JS_ASSERT(!cx->thread->titleToShare);
cx->thread->titleToShare = title;
@ -661,21 +638,6 @@ ClaimTitle(JSTitle *title, JSContext *cx)
#endif
PR_WaitCondVar(rt->titleSharingDone, PR_INTERVAL_NO_TIMEOUT);
JS_ASSERT(stat != PR_FAILURE);
js_RecountRequestsAfterGC(rt, requestDebit);
/*
* Don't clear titleToShare until after we're through waiting on
* all condition variables protected by rt->gcLock -- that includes
* rt->titleSharingDone *and* rt->gcDone (hidden in the call to
* js_RecountRequestsAfterGC immediately above).
*
* Otherwise, the GC could easily deadlock with another thread that
* owns a title wanted by a finalizer. By keeping cx->titleToShare
* set till here, we ensure that such deadlocks are detected, which
* results in the finalized object's title being shared (it must, of
* course, have other, live objects sharing it).
*/
cx->thread->titleToShare = NULL;
}
@ -693,24 +655,15 @@ js_ShareWaitingTitles(JSContext *cx)
todop = &cx->runtime->titleSharingTodo;
shared = false;
while ((title = *todop) != NO_TITLE_SHARING_TODO) {
if (title->ownercx != cx) {
if (title->ownercx->thread != cx->thread) {
todop = &title->u.link;
continue;
}
*todop = title->u.link;
title->u.link = NULL; /* null u.link for sanity ASAP */
title->u.link = NULL; /* null u.link for sanity ASAP */
/*
* If JSScope::drop returns false, we held the last ref to scope. The
* waiting thread(s) must have been killed, after which the GC
* collected the object that held this scope. Unlikely, because it
* requires that the GC ran (e.g., from an operation callback)
* during this request, but possible.
*/
if (TITLE_TO_SCOPE(title)->drop(cx, NULL)) {
FinishSharingTitle(cx, title); /* set ownercx = NULL */
shared = true;
}
FinishSharingTitle(cx, title); /* set ownercx = NULL */
shared = true;
}
if (shared)
JS_NOTIFY_ALL_CONDVAR(cx->runtime->titleSharingDone);

8
js/src/jsobj.cpp
View File

@ -3860,12 +3860,8 @@ js_InitClass(JSContext *cx, JSObject *obj, JSObject *parent_proto,
*
* All callers of JSObject::initSharingEmptyScope depend on this.
*/
{
JSScope *scope = OBJ_SCOPE(proto)->getEmptyScope(cx, clasp);
if (!scope)
goto bad;
scope->drop(cx, NULL);
}
if (!OBJ_SCOPE(proto)->ensureEmptyScope(cx, clasp))
goto bad;
/* If this is a standard class, cache its prototype. */
if (key != JSProto_Null && !js_SetClassObject(cx, obj, key, ctor))

36
js/src/jsscope.h
View File

@ -285,7 +285,7 @@ struct JSScope : public JSObjectMap
static void destroy(JSContext *cx, JSScope *scope);
inline void hold();
inline bool drop(JSContext *cx, JSObject *obj);
inline void drop(JSContext *cx, JSObject *obj);
/*
* Return an immutable, shareable, empty scope with the same ops as this
@ -296,6 +296,8 @@ struct JSScope : public JSObjectMap
*/
inline JSEmptyScope *getEmptyScope(JSContext *cx, JSClass *clasp);
inline bool ensureEmptyScope(JSContext *cx, JSClass *clasp);
inline bool canProvideEmptyScope(JSObjectOps *ops, JSClass *clasp);
JSScopeProperty *lookup(jsid id);
@ -796,6 +798,22 @@ JSScope::getEmptyScope(JSContext *cx, JSClass *clasp)
return createEmptyScope(cx, clasp);
}
inline bool
JSScope::ensureEmptyScope(JSContext *cx, JSClass *clasp)
{
if (emptyScope) {
JS_ASSERT(clasp == emptyScope->clasp);
return true;
}
if (!createEmptyScope(cx, clasp))
return false;
/* We are going to have only single ref to the scope. */
JS_ASSERT(emptyScope->nrefs == 2);
emptyScope->nrefs = 1;
return true;
}
inline void
JSScope::hold()
{
@ -803,23 +821,23 @@ JSScope::hold()
JS_ATOMIC_INCREMENT(&nrefs);
}
inline bool
inline void
JSScope::drop(JSContext *cx, JSObject *obj)
{
#ifdef JS_THREADSAFE
/* We are called from only js_ShareWaitingTitles and js_FinalizeObject. */
JS_ASSERT(!obj || CX_THREAD_IS_RUNNING_GC(cx));
/*
* We are called only from js_FinalizeObject and can avoid the overhead of
* JS_ATOMIC_DECREMENT.
*/
JS_ASSERT(CX_THREAD_IS_RUNNING_GC(cx));
#endif
JS_ASSERT(nrefs > 0);
--nrefs;
if (nrefs == 0) {
if (nrefs == 0)
destroy(cx, this);
return false;
}
if (object == obj)
else if (object == obj)
object = NULL;
return true;
}
inline bool