Bug 1119550 - Stop using volatile to "synchronize" majorGCRequested; r=jonco

js/src/gc/GCRuntime.h

@@ -7,6 +7,8 @@
 #ifndef gc_GCRuntime_h
 #define gc_GCRuntime_h
 
+#include "mozilla/Atomics.h"
+
 #include "jsgc.h"
 
 #include "gc/Heap.h"
@@ -483,7 +485,9 @@ class GCRuntime
     bool areGrayBitsValid() { return grayBitsValid; }
     void setGrayBitsInvalid() { grayBitsValid = false; }
 
-    bool isGcNeeded() { return minorGCRequested || majorGCRequested; }
+    bool minorGCRequested() const { return minorGCTriggerReason != JS::gcreason::NO_REASON; }
+    bool majorGCRequested() const { return majorGCTriggerReason != JS::gcreason::NO_REASON; }
+    bool isGcNeeded() { return minorGCRequested() || majorGCRequested(); }
 
     double computeHeapGrowthFactor(size_t lastBytes);
     size_t computeTriggerBytes(double growthFactor, size_t lastBytes);
@@ -699,10 +703,8 @@ class GCRuntime
      */
     bool grayBitsValid;
 
-    volatile uintptr_t majorGCRequested;
-    JS::gcreason::Reason majorGCTriggerReason;
+    mozilla::Atomic<JS::gcreason::Reason, mozilla::Relaxed> majorGCTriggerReason;
 
-    bool minorGCRequested;
     JS::gcreason::Reason minorGCTriggerReason;
 
     /* Incremented at the start of every major GC. */

js/src/jsgc.cpp

@@ -1098,9 +1098,7 @@ GCRuntime::GCRuntime(JSRuntime *rt) :
     decommitThreshold(32 * 1024 * 1024),
     cleanUpEverything(false),
     grayBitsValid(false),
-    majorGCRequested(0),
     majorGCTriggerReason(JS::gcreason::NO_REASON),
-    minorGCRequested(false),
     minorGCTriggerReason(JS::gcreason::NO_REASON),
     majorGCNumber(0),
     jitReleaseNumber(0),
@@ -3144,10 +3142,9 @@ js::MarkCompartmentActive(InterpreterFrame *fp)
 void
 GCRuntime::requestMajorGC(JS::gcreason::Reason reason)
 {
-    if (majorGCRequested)
+    if (majorGCRequested())
         return;
 
-    majorGCRequested = true;
     majorGCTriggerReason = reason;
     rt->requestInterrupt(JSRuntime::RequestInterruptUrgent);
 }
@@ -3156,10 +3153,9 @@ void
 GCRuntime::requestMinorGC(JS::gcreason::Reason reason)
 {
     MOZ_ASSERT(CurrentThreadCanAccessRuntime(rt));
-    if (minorGCRequested)
+    if (minorGCRequested())
         return;
 
-    minorGCRequested = true;
     minorGCTriggerReason = reason;
     rt->requestInterrupt(JSRuntime::RequestInterruptUrgent);
 }
@@ -6059,7 +6055,7 @@ GCRuntime::gcCycle(bool incremental, SliceBudget &budget, JS::gcreason::Reason r
 
     AutoTraceSession session(rt, MajorCollecting);
 
-    majorGCRequested = false;
+    majorGCTriggerReason = JS::gcreason::NO_REASON;
     interFrameGC = true;
 
     number++;
@@ -6441,7 +6437,7 @@ GCRuntime::onOutOfMallocMemory(const AutoLockGC &lock)
 void
 GCRuntime::minorGCImpl(JS::gcreason::Reason reason, Nursery::TypeObjectList *pretenureTypes)
 {
-    minorGCRequested = false;
+    minorGCTriggerReason = JS::gcreason::NO_REASON;
     TraceLoggerThread *logger = TraceLoggerForMainThread(rt);
     AutoTraceLog logMinorGC(logger, TraceLogger_MinorGC);
     nursery.collect(rt, reason, pretenureTypes);
@@ -6490,14 +6486,14 @@ GCRuntime::gcIfNeeded(JSContext *cx /* = nullptr */)
 {
     // This method returns whether a major GC was performed.
 
-    if (minorGCRequested) {
+    if (minorGCRequested()) {
         if (cx)
             minorGC(cx, minorGCTriggerReason);
         else
             minorGC(minorGCTriggerReason);
     }
 
-    if (majorGCRequested) {
+    if (majorGCRequested()) {
         if (!isIncrementalGCInProgress())
             startGC(GC_NORMAL, majorGCTriggerReason);
         else