Bug 670967 - Part 1: Add mozilla::ScheduleMemoryPressureEvent(). r=bsmedberg

xpcom/threads/Makefile.in

@@ -64,6 +64,7 @@ CPPSRCS		= \
 		$(NULL)
 
 EXPORTS		= \
+		nsThread.h \
 		nsProcess.h \
 		nsEventQueue.h \
 		nsThreadUtilsInternal.h \

xpcom/threads/nsThread.cpp

@@ -45,7 +45,9 @@
 #include "nsCOMPtr.h"
 #include "prlog.h"
 #include "nsThreadUtilsInternal.h"
+#include "nsIObserverService.h"
 #include "mozilla/HangMonitor.h"
+#include "mozilla/Services.h"
 
 #define HAVE_UALARM _BSD_SOURCE || (_XOPEN_SOURCE >= 500 ||                 \
                       _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED) &&           \
@@ -81,6 +83,23 @@ NS_DECL_CI_INTERFACE_GETTER(nsThread)
 
 nsIThreadObserver* nsThread::sGlobalObserver;
 
+namespace mozilla {
+
+// Fun fact: Android's GCC won't convert bool* to PRInt32*, so we can't
+// PR_ATOMIC_SET a bool.
+static PRInt32 sMemoryPressurePending = 0;
+
+/*
+ * It's important that this function not acquire any locks, nor do anything
+ * which might cause malloc to run.
+ */
+void ScheduleMemoryPressureEvent()
+{
+  PR_ATOMIC_SET(&sMemoryPressurePending, 1);
+}
+
+};
+
 //-----------------------------------------------------------------------------
 // Because we do not have our own nsIFactory, we have to implement nsIClassInfo
 // somewhat manually.
@@ -577,6 +596,22 @@ nsThread::ProcessNextEvent(bool mayWait, bool *result)
   if (MAIN_THREAD == mIsMainThread && mayWait && !ShuttingDown())
     HangMonitor::Suspend();
 
+  // Fire a memory pressure notification, if we're the main thread and one is
+  // pending.
+  if (MAIN_THREAD == mIsMainThread && !ShuttingDown()) {
+    bool mpPending = PR_ATOMIC_SET(&sMemoryPressurePending, 0);
+    if (mpPending) {
+      nsCOMPtr<nsIObserverService> os = services::GetObserverService();
+      if (os) {
+        os->NotifyObservers(nsnull, "memory-pressure",
+                            NS_LITERAL_STRING("low-memory").get());
+      }
+      else {
+        NS_WARNING("Can't get observer service!");
+      }
+    }
+  }
+
   bool notifyGlobalObserver = (sGlobalObserver != nsnull);
   if (notifyGlobalObserver) 
     sGlobalObserver->OnProcessNextEvent(this, mayWait && !ShuttingDown(),

xpcom/threads/nsThread.h

@@ -178,4 +178,16 @@ private:
   nsresult mResult;
 };
 
+namespace mozilla {
+
+/**
+ * This function causes the main thread to fire a memory pressure event at its
+ * next available opportunity.
+ *
+ * You may call this function from any thread.
+ */
+void ScheduleMemoryPressureEvent();
+
+} // namespace mozilla
+
 #endif  // nsThread_h__