Bug 1359653: Part 9 - Observe "startupcache-invalidate" and flush the cache when received. r=erahm

Flushing the cache at startup is already handled automatically by the
AppStartup code, which removes the entire startupCache directory when
necessary. The add-on manager requires being able to flush the cache at
runtime, though, for the sake of updating bootstrapped add-ons.

MozReview-Commit-ID: LIdiNHrXYXu

js/xpconnect/loader/ScriptPreloader.cpp

@@ -29,6 +29,7 @@
 #define DELAYED_STARTUP_TOPIC "browser-delayed-startup-finished"
 #define CLEANUP_TOPIC "xpcom-shutdown"
 #define SHUTDOWN_TOPIC "quit-application-granted"
+#define CACHE_FLUSH_TOPIC "startupcache-invalidate"
 
 namespace mozilla {
 namespace {
@@ -124,6 +125,7 @@ ScriptPreloader::ScriptPreloader()
     obs->AddObserver(this, DELAYED_STARTUP_TOPIC, false);
     obs->AddObserver(this, SHUTDOWN_TOPIC, false);
     obs->AddObserver(this, CLEANUP_TOPIC, false);
+    obs->AddObserver(this, CACHE_FLUSH_TOPIC, false);
 
     AutoSafeJSAPI jsapi;
     JS_AddExtraGCRootsTracer(jsapi.cx(), TraceOp, this);
@@ -161,6 +163,44 @@ ScriptPreloader::Cleanup()
     UnregisterWeakMemoryReporter(this);
 }
 
+void
+ScriptPreloader::FlushScripts(LinkedList<CachedScript>& scripts)
+{
+    for (auto next = scripts.getFirst(); next; ) {
+        auto script = next;
+        next = script->getNext();
+
+        // We can only purge finished scripts here. Async scripts that are
+        // still being parsed off-thread have a non-refcounted reference to
+        // this script, which needs to stay alive until they finish parsing.
+        if (script->mReadyToExecute) {
+            script->Cancel();
+            script->remove();
+            delete script;
+        }
+    }
+}
+
+void
+ScriptPreloader::FlushCache()
+{
+    MonitorAutoLock mal(mMonitor);
+
+    FlushScripts(mSavedScripts);
+    FlushScripts(mRestoredScripts);
+
+    // If we've already finished saving the cache at this point, start a new
+    // delayed save operation. This will write out an empty cache file in place
+    // of any cache file we've already written out this session, which will
+    // prevent us from falling back to the current session's cache file on the
+    // next startup.
+    if (mSaveComplete) {
+        mSaveComplete = false;
+
+        Unused << NS_NewNamedThread("SaveScripts",
+                                    getter_AddRefs(mSaveThread), this);
+    }
+}
 
 nsresult
 ScriptPreloader::Observe(nsISupports* subject, const char* topic, const char16_t* data)
@@ -179,6 +219,8 @@ ScriptPreloader::Observe(nsISupports* subject, const char* topic, const char16_t
         ForceWriteCacheFile();
     } else if (!strcmp(topic, CLEANUP_TOPIC)) {
         Cleanup();
+    } else if (!strcmp(topic, CACHE_FLUSH_TOPIC)) {
+        FlushCache();
     }
 
     return NS_OK;
@@ -609,6 +651,7 @@ ScriptPreloader::OffThreadDecodeCallback(void* token, void* context)
     mal.NotifyAll();
 }
 
+inline
 ScriptPreloader::CachedScript::CachedScript(InputBuffer& buf)
 {
     Code(buf);
@@ -631,6 +674,20 @@ ScriptPreloader::CachedScript::XDREncode(JSContext* cx)
     return false;
 }
 
+void
+ScriptPreloader::CachedScript::Cancel()
+{
+    if (mToken) {
+        GetSingleton().mMonitor.AssertCurrentThreadOwns();
+
+        AutoSafeJSAPI jsapi;
+        JS::CancelOffThreadScriptDecoder(jsapi.cx(), mToken);
+
+        mReadyToExecute = true;
+        mToken = nullptr;
+    }
+}
+
 JSScript*
 ScriptPreloader::CachedScript::GetJSScript(JSContext* cx)
 {