Bug 1296484 - Automatically run a CC if COMPARTMENT_REVIVED GC ends mostly gray; r=jonco,r=mccr8

--HG--
extra : rebase_source : 26aa07342c0b286d772422401bd7d5dd4efbb2fa

js/public/GCAPI.h

@@ -386,6 +386,16 @@ using GCNurseryCollectionCallback = void(*)(JSContext* cx, GCNurseryProgress pro
 extern JS_PUBLIC_API(GCNurseryCollectionCallback)
 SetGCNurseryCollectionCallback(JSContext* cx, GCNurseryCollectionCallback callback);
 
+typedef void
+(* DoCycleCollectionCallback)(JSContext* cx);
+
+/**
+ * The purge gray callback is called after any COMPARTMENT_REVIVED GC in which
+ * the majority of compartments have been marked gray.
+ */
+extern JS_PUBLIC_API(DoCycleCollectionCallback)
+SetDoCycleCollectionCallback(JSContext* cx, DoCycleCollectionCallback callback);
+
 /**
  * Incremental GC defaults to enabled, but may be disabled for testing or in
  * embeddings that have not yet implemented barriers on their native classes.

js/src/gc/GCRuntime.h

@@ -778,6 +778,8 @@ class GCRuntime
     JS::GCSliceCallback setSliceCallback(JS::GCSliceCallback callback);
     JS::GCNurseryCollectionCallback setNurseryCollectionCallback(
         JS::GCNurseryCollectionCallback callback);
+    JS::DoCycleCollectionCallback setDoCycleCollectionCallback(JS::DoCycleCollectionCallback callback);
+    void callDoCycleCollectionCallback(JSContext* cx);
 
     void setFullCompartmentChecks(bool enable);
 
@@ -947,6 +949,7 @@ class GCRuntime
     void traceRuntimeCommon(JSTracer* trc, TraceOrMarkRuntime traceOrMark,
                             AutoLockForExclusiveAccess& lock);
     void bufferGrayRoots();
+    void maybeDoCycleCollection();
     void markCompartments();
     IncrementalProgress drainMarkStack(SliceBudget& sliceBudget, gcstats::Phase phase);
     template <class CompartmentIterT> void markWeakReferences(gcstats::Phase phase);
@@ -1305,6 +1308,7 @@ class GCRuntime
     bool fullCompartmentChecks;
 
     Callback<JSGCCallback> gcCallback;
+    Callback<JS::DoCycleCollectionCallback> gcDoCycleCollectionCallback;
     Callback<JSObjectsTenuredCallback> tenuredCallback;
     CallbackVector<JSFinalizeCallback> finalizeCallbacks;
     CallbackVector<JSWeakPointerZoneGroupCallback> updateWeakPointerZoneGroupCallbacks;

js/src/jsgc.cpp

@@ -1481,6 +1481,21 @@ GCRuntime::setNurseryCollectionCallback(JS::GCNurseryCollectionCallback callback
     return stats.setNurseryCollectionCallback(callback);
 }
 
+JS::DoCycleCollectionCallback
+GCRuntime::setDoCycleCollectionCallback(JS::DoCycleCollectionCallback callback)
+{
+    auto prior = gcDoCycleCollectionCallback;
+    gcDoCycleCollectionCallback = Callback<JS::DoCycleCollectionCallback>(callback, nullptr);
+    return prior.op;
+}
+
+void
+GCRuntime::callDoCycleCollectionCallback(JSContext* cx)
+{
+    if (gcDoCycleCollectionCallback.op)
+        gcDoCycleCollectionCallback.op(cx);
+}
+
 bool
 GCRuntime::addRoot(Value* vp, const char* name)
 {
@@ -6171,6 +6186,31 @@ GCRuntime::scanZonesBeforeGC()
     return zoneStats;
 }
 
+// The GC can only clean up scheduledForDestruction compartments that were
+// marked live by a barrier (e.g. by RemapWrappers from a navigation event).
+// It is also common to have compartments held live because they are part of a
+// cycle in gecko, e.g. involving the HTMLDocument wrapper. In this case, we
+// need to run the CycleCollector in order to remove these edges before the
+// compartment can be freed.
+void
+GCRuntime::maybeDoCycleCollection()
+{
+    const static double ExcessiveGrayCompartments = 0.8;
+    const static size_t LimitGrayCompartments = 200;
+
+    size_t compartmentsTotal = 0;
+    size_t compartmentsGray = 0;
+    for (CompartmentsIter c(rt, SkipAtoms); !c.done(); c.next()) {
+        ++compartmentsTotal;
+        GlobalObject* global = c->unsafeUnbarrieredMaybeGlobal();
+        if (global && global->asTenured().isMarked(GRAY))
+            ++compartmentsGray;
+    }
+    double grayFraction = double(compartmentsGray) / double(compartmentsTotal);
+    if (grayFraction > ExcessiveGrayCompartments || compartmentsGray > LimitGrayCompartments)
+        callDoCycleCollectionCallback(rt->contextFromMainThread());
+}
+
 void
 GCRuntime::checkCanCallAPI()
 {
@@ -6251,6 +6291,9 @@ GCRuntime::collect(bool nonincrementalByAPI, SliceBudget budget, JS::gcreason::R
         repeat = (poked && cleanUpEverything) || wasReset || repeatForDeadZone;
     } while (repeat);
 
+    if (reason == JS::gcreason::COMPARTMENT_REVIVED)
+        maybeDoCycleCollection();
+
 #ifdef JS_GC_ZEAL
     if (shouldCompact() && rt->hasZealMode(ZealMode::CheckHeapOnMovingGC)) {
         gcstats::AutoPhase ap(rt->gc.stats, gcstats::PHASE_TRACE_HEAP);
@@ -7169,6 +7212,12 @@ JS::SetGCSliceCallback(JSContext* cx, GCSliceCallback callback)
     return cx->gc.setSliceCallback(callback);
 }
 
+JS_PUBLIC_API(JS::DoCycleCollectionCallback)
+JS::SetDoCycleCollectionCallback(JSContext* cx, JS::DoCycleCollectionCallback callback)
+{
+    return cx->gc.setDoCycleCollectionCallback(callback);
+}
+
 JS_PUBLIC_API(JS::GCNurseryCollectionCallback)
 JS::SetGCNurseryCollectionCallback(JSContext* cx, GCNurseryCollectionCallback callback)
 {

js/xpconnect/src/XPCJSRuntime.cpp

@@ -23,6 +23,7 @@
 #include "nsIObserverService.h"
 #include "nsIDebug2.h"
 #include "nsIDocShell.h"
+#include "nsIRunnable.h"
 #include "amIAddonManager.h"
 #include "nsPIDOMWindow.h"
 #include "nsPrintfCString.h"
@@ -720,6 +721,21 @@ XPCJSRuntime::GCSliceCallback(JSContext* cx,
         (*self->mPrevGCSliceCallback)(cx, progress, desc);
 }
 
+/* static */ void
+XPCJSRuntime::DoCycleCollectionCallback(JSContext* cx)
+{
+    // The GC has detected that a CC at this point would collect a tremendous
+    // amount of garbage that is being revivified unnecessarily.
+    NS_DispatchToMainThread(NS_NewRunnableFunction([](){nsJSContext::CycleCollectNow(nullptr);}));
+
+    XPCJSRuntime* self = nsXPConnect::GetRuntimeInstance();
+    if (!self)
+        return;
+
+    if (self->mPrevDoCycleCollectionCallback)
+        (*self->mPrevDoCycleCollectionCallback)(cx);
+}
+
 void
 XPCJSRuntime::CustomGCCallback(JSGCStatus status)
 {
@@ -3481,6 +3497,8 @@ XPCJSRuntime::Initialize()
     JS_SetSizeOfIncludingThisCompartmentCallback(cx, CompartmentSizeOfIncludingThisCallback);
     JS_SetCompartmentNameCallback(cx, CompartmentNameCallback);
     mPrevGCSliceCallback = JS::SetGCSliceCallback(cx, GCSliceCallback);
+    mPrevDoCycleCollectionCallback = JS::SetDoCycleCollectionCallback(cx,
+            DoCycleCollectionCallback);
     JS_AddFinalizeCallback(cx, FinalizeCallback, nullptr);
     JS_AddWeakPointerZoneGroupCallback(cx, WeakPointerZoneGroupCallback, this);
     JS_AddWeakPointerCompartmentCallback(cx, WeakPointerCompartmentCallback, this);

js/xpconnect/src/xpcprivate.h

@@ -551,6 +551,7 @@ public:
     static void GCSliceCallback(JSContext* cx,
                                 JS::GCProgress progress,
                                 const JS::GCDescription& desc);
+    static void DoCycleCollectionCallback(JSContext* cx);
     static void FinalizeCallback(JSFreeOp* fop,
                                  JSFinalizeStatus status,
                                  bool isZoneGC,
@@ -628,6 +629,7 @@ private:
     nsTArray<xpcGCCallback> extraGCCallbacks;
     RefPtr<WatchdogManager> mWatchdogManager;
     JS::GCSliceCallback mPrevGCSliceCallback;
+    JS::DoCycleCollectionCallback mPrevDoCycleCollectionCallback;
     JS::PersistentRootedObject mUnprivilegedJunkScope;
     JS::PersistentRootedObject mPrivilegedJunkScope;
     JS::PersistentRootedObject mCompilationScope;