Bug 906001 - Improve tests and asserts around starting off thread parses while GC is active in the atoms zone, r=billm.

js/src/gc/Zone.cpp

@@ -76,6 +76,7 @@ Zone::setNeedsBarrier(bool needs, ShouldUpdateIon updateIon)
     if (needs && runtimeFromMainThread()->isAtomsZone(this))
         JS_ASSERT(!runtimeFromMainThread()->exclusiveThreadsPresent());
 
+    JS_ASSERT_IF(needs, canCollect());
     needsBarrier_ = needs;
 }
 

js/src/gc/Zone.h

@@ -189,20 +189,16 @@ struct Zone : private JS::shadow::Zone,
 
     void setGCState(CompartmentGCState state) {
         JS_ASSERT(runtimeFromMainThread()->isHeapBusy());
+        JS_ASSERT_IF(state != NoGC, canCollect());
         gcState = state;
     }
 
     void scheduleGC() {
-        JSRuntime *rt = runtimeFromMainThread();
-        JS_ASSERT(!rt->isHeapBusy());
+        JS_ASSERT(!runtimeFromMainThread()->isHeapBusy());
 
-        /* Note: zones cannot be collected while in use by other threads. */
-        if (usedByExclusiveThread)
-            return;
-        if (rt->isAtomsZone(this) && rt->exclusiveThreadsPresent())
-            return;
-
-        gcScheduled = true;
+        // Ignore attempts to schedule GCs on zones which can't be collected.
+        if (canCollect())
+            gcScheduled = true;
     }
 
     void unscheduleGC() {
@@ -217,6 +213,16 @@ struct Zone : private JS::shadow::Zone,
         gcPreserveCode = preserving;
     }
 
+    bool canCollect() {
+        // Zones cannot be collected while in use by other threads.
+        if (usedByExclusiveThread)
+            return false;
+        JSRuntime *rt = runtimeFromMainThread();
+        if (rt->isAtomsZone(this) && rt->exclusiveThreadsPresent())
+            return false;
+        return true;
+    }
+
     bool wasGCStarted() const {
         return gcState != NoGC;
     }

js/src/jsapi.cpp

@@ -4847,7 +4847,7 @@ JS::CanCompileOffThread(JSContext *cx, const CompileOptions &options)
     // atoms compartment, to avoid triggering barriers. Outside the atoms
     // compartment, the compilation will use a new zone which doesn't require
     // barriers itself.
-    if (cx->runtime()->atomsZoneNeedsBarrier())
+    if (cx->runtime()->activeGCInAtomsZone())
         return false;
 
     // Blacklist filenames which cause mysterious assertion failures in

js/src/jscompartment.h

@@ -401,12 +401,6 @@ JSRuntime::isAtomsZone(JS::Zone *zone)
     return zone == atomsCompartment_->zone();
 }
 
-inline bool
-JSRuntime::atomsZoneNeedsBarrier()
-{
-    return atomsCompartment_->zone()->needsBarrier();
-}
-
 // For use when changing the debug mode flag on one or more compartments.
 // Do not run scripts in any compartment that is scheduled for GC using this
 // object. See comment in updateForDebugMode.

js/src/vm/Runtime.cpp

@@ -716,6 +716,13 @@ JSRuntime::onOutOfMemory(void *p, size_t nbytes, JSContext *cx)
     return NULL;
 }
 
+bool
+JSRuntime::activeGCInAtomsZone()
+{
+    Zone *zone = atomsCompartment_->zone();
+    return zone->needsBarrier() || zone->isGCScheduled() || zone->wasGCStarted();
+}
+
 #ifdef JS_THREADSAFE
 
 void

js/src/vm/Runtime.h

@@ -1415,7 +1415,7 @@ struct JSRuntime : public JS::shadow::Runtime,
     // The atoms compartment is the only one in its zone.
     inline bool isAtomsZone(JS::Zone *zone);
 
-    inline bool atomsZoneNeedsBarrier();
+    bool activeGCInAtomsZone();
 
     union {
         /*