jslock.c

java script test programing source code

         * If scope->u.link is non-null, scope has already been inserted on
         * the rt->scopeSharingTodo list, because another thread's context
         * already wanted to lock scope while ownercx was running a request.
         * We can't claim any scope whose u.link is non-null at this point,
         * even if ownercx->requestDepth is 0 (see below where we suspend our
         * request before waiting on rt->scopeSharingDone).
         */
        if (!scope->u.link &&
            (!js_ValidContextPointer(rt, ownercx) ||
             !ownercx->requestDepth ||
             ownercx->thread == cx->thread)) {
            JS_ASSERT(scope->u.count == 0);
            scope->ownercx = cx;
            JS_UNLOCK_GC(rt);
            JS_RUNTIME_METER(rt, claimedScopes);
            return JS_TRUE;
        }

        /*
         * Avoid deadlock if scope's owner context is waiting on a scope that
         * we own, by revoking scope's ownership.  This approach to deadlock
         * avoidance works because the engine never nests scope locks, except
         * for the notable case of js_SetProtoOrParent (see jsobj.c).
         *
         * If cx could hold locks on ownercx->scopeToShare, or if ownercx
         * could hold locks on scope, we would need to keep reentrancy counts
         * for all such "flyweight" (ownercx != NULL) locks, so that control
         * would unwind properly once these locks became "thin" or "fat".
         * Apart from the js_SetProtoOrParent exception, the engine promotes
         * a scope from exclusive to shared access only when locking, never
         * when holding or unlocking.
         *
         * If ownercx's thread is calling js_SetProtoOrParent, trying to lock
         * the inner scope (the scope of the object being set as the prototype
         * of the outer object), ShareScope will find the outer object's scope
         * at rt->setSlotScope.  If it's the same as scope, we give it a lock
         * held by ownercx's thread with reentrancy count of 1, then we return
         * here and break.  After that we unwind to js_[GS]etSlotThreadSafe or
         * js_LockScope (our caller), where we wait on the newly-fattened lock
         * until ownercx's thread unwinds from js_SetProtoOrParent.
         *
         * Avoid deadlock before any of this scope/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 scope wanted by the GC (from
         * a finalizer) that can't be claimed must be slated for sharing.
         */
        if (rt->gcThread == cx->thread ||
            (ownercx->scopeToShare &&
             WillDeadlock(ownercx->scopeToShare, cx))) {
            ShareScope(rt, scope);
            break;
        }

        /*
         * Thanks to the non-zero NO_SCOPE_SHARING_TODO link terminator, we
         * can decide whether scope is on rt->scopeSharingTodo with a single
         * non-null test, and avoid double-insertion bugs.
         */
        if (!scope->u.link) {
            scope->u.link = rt->scopeSharingTodo;
            rt->scopeSharingTodo = scope;
            js_HoldObjectMap(cx, &scope->map);
        }

        /*
         * Inline JS_SuspendRequest before we wait on rt->scopeSharingDone,
         * saving and clearing cx->requestDepth so we don't deadlock if the
         * GC needs to run on ownercx.
         *
         * Unlike JS_SuspendRequest and JS_EndRequest, we must take care not
         * to decrement rt->requestCount if cx is active on the GC's thread,
         * because the GC has already reduced rt->requestCount to exclude all
         * such such contexts.
         */
        saveDepth = cx->requestDepth;
        if (saveDepth) {
            cx->requestDepth = 0;
            if (rt->gcThread != cx->thread) {
                JS_ASSERT(rt->requestCount > 0);
                rt->requestCount--;
                if (rt->requestCount == 0)
                    JS_NOTIFY_REQUEST_DONE(rt);
            }
        }

        /*
         * We know that some other thread's context owns scope, which is now
         * linked onto rt->scopeSharingTodo, awaiting the end of that other
         * thread's request.  So it is safe to wait on rt->scopeSharingDone.
         */
        cx->scopeToShare = scope;
        stat = PR_WaitCondVar(rt->scopeSharingDone, PR_INTERVAL_NO_TIMEOUT);
        JS_ASSERT(stat != PR_FAILURE);

        /*
         * Inline JS_ResumeRequest after waiting on rt->scopeSharingDone,
         * restoring cx->requestDepth.  Same note as above for the inlined,
         * specialized JS_SuspendRequest code: beware rt->gcThread.
         */
        if (saveDepth) {
            if (rt->gcThread != cx->thread) {
                while (rt->gcLevel > 0)
                    JS_AWAIT_GC_DONE(rt);
                rt->requestCount++;
            }
            cx->requestDepth = saveDepth;
        }

        /*
         * Don't clear cx->scopeToShare until after we're through waiting on
         * all condition variables protected by rt->gcLock -- that includes
         * rt->scopeSharingDone *and* rt->gcDone (hidden in JS_AWAIT_GC_DONE,
         * in the inlined JS_ResumeRequest code immediately above).
         *
         * Otherwise, the GC could easily deadlock with another thread that
         * owns a scope wanted by a finalizer.  By keeping cx->scopeToShare
         * set till here, we ensure that such deadlocks are detected, which
         * results in the finalized object's scope being shared (it must, of
         * course, have other, live objects sharing it).
         */
        cx->scopeToShare = NULL;
    }

    JS_UNLOCK_GC(rt);
    return JS_FALSE;
}

/* Exported to js.c, which calls it via OBJ_GET_* and JSVAL_IS_* macros. */
JS_FRIEND_API(jsval)
js_GetSlotThreadSafe(JSContext *cx, JSObject *obj, uint32 slot)
{
    jsval v;
    JSScope *scope;
#ifndef NSPR_LOCK
    JSThinLock *tl;
    jsword me;
#endif

    /*
     * We handle non-native objects via JSObjectOps.getRequiredSlot, treating
     * all slots starting from 0 as required slots.  A property definition or
     * some prior arrangement must have allocated slot.
     *
     * Note once again (see jspubtd.h, before JSGetRequiredSlotOp's typedef)
     * the crucial distinction between a |required slot number| that's passed
     * to the get/setRequiredSlot JSObjectOps, and a |reserved slot index|
     * passed to the JS_Get/SetReservedSlot APIs.
     */
    if (!OBJ_IS_NATIVE(obj))
        return OBJ_GET_REQUIRED_SLOT(cx, obj, slot);

    /*
     * Native object locking is inlined here to optimize the single-threaded
     * and contention-free multi-threaded cases.
     */
    scope = OBJ_SCOPE(obj);
    JS_ASSERT(scope->ownercx != cx);
    JS_ASSERT(obj->slots && slot < obj->map->freeslot);

    /*
     * Avoid locking if called from the GC (see GC_AWARE_GET_SLOT in jsobj.h).
     * Also avoid locking an object owning a sealed scope.  If neither of those
     * special cases applies, try to claim scope's flyweight lock from whatever
     * context may have had it in an earlier request.
     */
    if (CX_THREAD_IS_RUNNING_GC(cx) ||
        (SCOPE_IS_SEALED(scope) && scope->object == obj) ||
        (scope->ownercx && ClaimScope(scope, cx))) {
        return obj->slots[slot];
    }

#ifndef NSPR_LOCK
    tl = &scope->lock;
    me = CX_THINLOCK_ID(cx);
    JS_ASSERT(CURRENT_THREAD_IS_ME(me));
    if (js_CompareAndSwap(&tl->owner, 0, me)) {
        /*
         * Got the lock with one compare-and-swap.  Even so, someone else may
         * have mutated obj so it now has its own scope and lock, which would
         * require either a restart from the top of this routine, or a thin
         * lock release followed by fat lock acquisition.
         */
        if (scope == OBJ_SCOPE(obj)) {
            v = obj->slots[slot];
            if (!js_CompareAndSwap(&tl->owner, me, 0)) {
                /* Assert that scope locks never revert to flyweight. */
                JS_ASSERT(scope->ownercx != cx);
                LOGIT(scope, '1');
                scope->u.count = 1;
                js_UnlockObj(cx, obj);
            }
            return v;
        }
        if (!js_CompareAndSwap(&tl->owner, me, 0))
            js_Dequeue(tl);
    }
    else if (Thin_RemoveWait(ReadWord(tl->owner)) == me) {
        return obj->slots[slot];
    }
#endif

    js_LockObj(cx, obj);
    v = obj->slots[slot];

    /*
     * Test whether cx took ownership of obj's scope during js_LockObj.
     *
     * This does not mean that a given scope reverted to flyweight from "thin"
     * or "fat" -- it does mean that obj's map pointer changed due to another
     * thread setting a property, requiring obj to cease sharing a prototype
     * object's scope (whose lock was not flyweight, else we wouldn't be here
     * in the first place!).
     */
    scope = OBJ_SCOPE(obj);
    if (scope->ownercx != cx)
        js_UnlockScope(cx, scope);
    return v;
}

void
js_SetSlotThreadSafe(JSContext *cx, JSObject *obj, uint32 slot, jsval v)
{
    JSScope *scope;
#ifndef NSPR_LOCK
    JSThinLock *tl;
    jsword me;
#endif

    /* Any string stored in a thread-safe object must be immutable. */
    if (JSVAL_IS_STRING(v))
        MAKE_STRING_IMMUTABLE(cx->runtime, v, &v);

    /*
     * We handle non-native objects via JSObjectOps.setRequiredSlot, as above
     * for the Get case.
     */
    if (!OBJ_IS_NATIVE(obj)) {
        OBJ_SET_REQUIRED_SLOT(cx, obj, slot, v);
        return;
    }

    /*
     * Native object locking is inlined here to optimize the single-threaded
     * and contention-free multi-threaded cases.
     */
    scope = OBJ_SCOPE(obj);
    JS_ASSERT(scope->ownercx != cx);
    JS_ASSERT(obj->slots && slot < obj->map->freeslot);

    /*
     * Avoid locking if called from the GC (see GC_AWARE_GET_SLOT in jsobj.h).
     * Also avoid locking an object owning a sealed scope.  If neither of those
     * special cases applies, try to claim scope's flyweight lock from whatever
     * context may have had it in an earlier request.
     */
    if (CX_THREAD_IS_RUNNING_GC(cx) ||
        (SCOPE_IS_SEALED(scope) && scope->object == obj) ||
        (scope->ownercx && ClaimScope(scope, cx))) {
        obj->slots[slot] = v;
        return;
    }

#ifndef NSPR_LOCK
    tl = &scope->lock;
    me = CX_THINLOCK_ID(cx);
    JS_ASSERT(CURRENT_THREAD_IS_ME(me));
    if (js_CompareAndSwap(&tl->owner, 0, me)) {
        if (scope == OBJ_SCOPE(obj)) {
            obj->slots[slot] = v;
            if (!js_CompareAndSwap(&tl->owner, me, 0)) {
                /* Assert that scope locks never revert to flyweight. */
                JS_ASSERT(scope->ownercx != cx);
                LOGIT(scope, '1');
                scope->u.count = 1;
                js_UnlockObj(cx, obj);
            }
            return;
        }
        if (!js_CompareAndSwap(&tl->owner, me, 0))
            js_Dequeue(tl);
    }
    else if (Thin_RemoveWait(ReadWord(tl->owner)) == me) {
        obj->slots[slot] = v;
        return;
    }
#endif

    js_LockObj(cx, obj);
    obj->slots[slot] = v;

    /*
     * Same drill as above, in js_GetSlotThreadSafe.  Note that we cannot
     * assume obj has its own mutable scope (where scope->object == obj) yet,
     * because OBJ_SET_SLOT is called for the "universal", common slots such
     * as JSSLOT_PROTO and JSSLOT_PARENT, without a prior js_GetMutableScope.
     * See also the JSPROP_SHARED attribute and its usage.
     */
    scope = OBJ_SCOPE(obj);
    if (scope->ownercx != cx)
        js_UnlockScope(cx, scope);
}

#ifndef NSPR_LOCK

static JSFatLock *
NewFatlock()
{
    JSFatLock *fl = (JSFatLock *)malloc(sizeof(JSFatLock)); /* for now */
    if (!fl) return NULL;
    fl->susp = 0;
    fl->next = NULL;
    fl->prevp = NULL;
    fl->slock = PR_NewLock();
    fl->svar = PR_NewCondVar(fl->slock);
    return fl;
}

static void
DestroyFatlock(JSFatLock *fl)
{
    PR_DestroyLock(fl->slock);
    PR_DestroyCondVar(fl->svar);
    free(fl);
}

static JSFatLock *
ListOfFatlocks(int listc)
{
    JSFatLock *m;
    JSFatLock *m0;
    int i;

    JS_ASSERT(listc>0);
    m0 = m = NewFatlock();
    for (i=1; i<listc; i++) {
        m->next = NewFatlock();
        m = m->next;
    }
    return m0;
}

static void
DeleteListOfFatlocks(JSFatLock *m)
{
    JSFatLock *m0;
    for (; m; m=m0) {
        m0 = m->next;
        DestroyFatlock(m);
    }
}

static JSFatLockTable *fl_list_table = NULL;
static uint32          fl_list_table_len = 0;
static uint32          fl_list_chunk_len = 0;

static JSFatLock *
GetFatlock(void *id)
{
    JSFatLock *m;

    uint32 i = GLOBAL_LOCK_INDEX(id);
    if (fl_list_table[i].free == NULL) {
#ifdef DEBUG
        if (fl_list_table[i].taken)
            printf("Ran out of fat locks!\n");
#endif
        fl_list_table[i].free = ListOfFatlocks(fl_list_chunk_len);
    }
    m = fl_list_table[i].free;
    fl_list_table[i].free = m->next;
    m->susp = 0;
    m->next = fl_list_table[i].taken;
    m->prevp = &fl_list_table[i].taken;
    if (fl_list_table[i].taken)
        fl_list_table[i].taken->prevp = &m->next;
    fl_list_table[i].taken = m;
    return m;
}

static void
PutFatlock(JSFatLock *m, void *id)
{
    uint32 i;
    if (m == NULL)
        return;

    /* Unlink m from fl_list_table[i].taken. */
    *m->prevp = m->next;
    if (m->next)
        m->next->prevp = m->prevp;

    /* Insert m in fl_list_table[i].free. */
    i = GLOBAL_LOCK_INDEX(id);
    m->next = fl_list_table[i].free;
    fl_list_table[i].free = m;
}

#endif /* !NSPR_LOCK */

JSBool
js_SetupLocks(int listc, int globc)
{
#ifndef NSPR_LOCK
    uint32 i;

    if (global_locks)
        return JS_TRUE;
#ifdef DEBUG
    if (listc > 10000 || listc < 0) /* listc == fat lock list chunk length */
        printf("Bad number %d in js_SetupLocks()!\n", listc);
    if (globc > 100 || globc < 0)   /* globc == number of global locks */
        printf("Bad number %d in js_SetupLocks()!\n", listc);
#endif
    global_locks_log2 = JS_CeilingLog2(globc);
    global_locks_mask = JS_BITMASK(global_locks_log2);
    global_lock_count = JS_BIT(global_locks_log2);
    global_locks = (PRLock **) malloc(global_lock_count * sizeof(PRLock*));
    if (!global_locks)
        return JS_FALSE;
    for (i = 0; i < global_lock_count; i++) {
        global_locks[i] = PR_NewLock();
        if (!global_locks[i]) {
            global_lock_count = i;
            js_CleanupLocks();
            return JS_FALSE;
        }
    }
    fl_list_table = (JSFatLockTable *) malloc(i * sizeof(JSFatLockTable));
    if (!fl_list_table) {
        js_CleanupLocks();
        return JS_FALSE;
    }
    fl_list_table_len = global_lock_count;
    for (i = 0; i < global_lock_count; i++)
        fl_list_table[i].free = fl_list_table[i].taken = NULL;