Bug 1102975 - Add a pref to control the content viewer expiration time in bfcache, r=khuey

--HG--
extra : rebase_source : 6fb403cdb1b73fa8e1f61945ddfd3bfe8e75a92d

b2g/app/b2g.js

@@ -99,6 +99,7 @@ pref("network.predictor.preserve", 50); // percentage of predictor data to keep
 /* session history */
 pref("browser.sessionhistory.max_total_viewers", 1);
 pref("browser.sessionhistory.max_entries", 50);
+pref("browser.sessionhistory.contentViewerTimeout", 360);
 
 /* session store */
 pref("browser.sessionstore.resume_session_once", false);

docshell/build/nsDocShellModule.cpp

@@ -53,7 +53,6 @@ Initialize()
   nsresult rv = nsSHistory::Startup();
   NS_ENSURE_SUCCESS(rv, rv);
 
-  nsSHEntryShared::Startup();
   return NS_OK;
 }
 

docshell/shistory/src/nsSHEntryShared.cpp

@@ -16,6 +16,7 @@
 #include "nsThreadUtils.h"
 #include "nsILayoutHistoryState.h"
 #include "mozilla/Attributes.h"
+#include "mozilla/Preferences.h"
 #include "nsISupportsArray.h"
 
 namespace dom = mozilla::dom;
@@ -26,19 +27,18 @@ uint64_t gSHEntrySharedID = 0;
 
 } // anonymous namespace
 
-// Hardcode this to time out unused content viewers after 30 minutes
-// XXX jlebar shouldn't this be a pref?
-#define CONTENT_VIEWER_TIMEOUT_SECONDS (30*60)
+#define CONTENT_VIEWER_TIMEOUT_SECONDS "browser.sessionhistory.contentViewerTimeout"
+// Default this to time out unused content viewers after 30 minutes
+#define CONTENT_VIEWER_TIMEOUT_SECONDS_DEFAULT (30*60)
 
 typedef nsExpirationTracker<nsSHEntryShared, 3> HistoryTrackerBase;
 class HistoryTracker MOZ_FINAL : public HistoryTrackerBase {
 public:
-  // Expire cached contentviewers after 20-30 minutes in the cache.
-  HistoryTracker() 
-    : HistoryTrackerBase(1000 * CONTENT_VIEWER_TIMEOUT_SECONDS / 2)
+  HistoryTracker(uint32_t aTimeout)
+    : HistoryTrackerBase(1000 * aTimeout / 2)
   {
   }
-  
+
 protected:
   virtual void NotifyExpired(nsSHEntryShared *aObj) {
     RemoveObject(aObj);
@@ -49,9 +49,15 @@ protected:
 static HistoryTracker *gHistoryTracker = nullptr;
 
 void
-nsSHEntryShared::Startup()
+nsSHEntryShared::EnsureHistoryTracker()
 {
-  gHistoryTracker = new HistoryTracker();
+  if (!gHistoryTracker) {
+    // nsExpirationTracker doesn't allow one to change the timer period,
+    // so just set it once when the history tracker is used for the first time.
+    gHistoryTracker = new HistoryTracker(
+      mozilla::Preferences::GetUint(CONTENT_VIEWER_TIMEOUT_SECONDS,
+                                    CONTENT_VIEWER_TIMEOUT_SECONDS_DEFAULT));
+  }
 }
 
 void
@@ -79,14 +85,16 @@ nsSHEntryShared::~nsSHEntryShared()
   RemoveFromExpirationTracker();
 
 #ifdef DEBUG
-  // Check that we're not still on track to expire.  We shouldn't be, because
-  // we just removed ourselves!
-  nsExpirationTracker<nsSHEntryShared, 3>::Iterator
-    iterator(gHistoryTracker);
+  if (gHistoryTracker) {
+    // Check that we're not still on track to expire.  We shouldn't be, because
+    // we just removed ourselves!
+    nsExpirationTracker<nsSHEntryShared, 3>::Iterator
+      iterator(gHistoryTracker);
 
-  nsSHEntryShared *elem;
-  while ((elem = iterator.Next()) != nullptr) {
-    NS_ASSERTION(elem != this, "Found dead entry still in the tracker!");
+    nsSHEntryShared *elem;
+    while ((elem = iterator.Next()) != nullptr) {
+      NS_ASSERTION(elem != this, "Found dead entry still in the tracker!");
+    }
   }
 #endif
 
@@ -118,7 +126,7 @@ nsSHEntryShared::Duplicate(nsSHEntryShared *aEntry)
 
 void nsSHEntryShared::RemoveFromExpirationTracker()
 {
-  if (GetExpirationState()->IsTracked()) {
+  if (gHistoryTracker && GetExpirationState()->IsTracked()) {
     gHistoryTracker->RemoveObject(this);
   }
 }
@@ -201,6 +209,7 @@ nsSHEntryShared::SetContentViewer(nsIContentViewer *aViewer)
   mContentViewer = aViewer;
 
   if (mContentViewer) {
+    EnsureHistoryTracker();
     gHistoryTracker->AddObject(this);
 
     nsCOMPtr<nsIDOMDocument> domDoc;

docshell/shistory/src/nsSHEntryShared.h

@@ -34,7 +34,7 @@ class nsSHEntryShared MOZ_FINAL : public nsIBFCacheEntry,
                                   public nsIMutationObserver
 {
   public:
-    static void Startup();
+    static void EnsureHistoryTracker();
     static void Shutdown();
 
     nsSHEntryShared();

mobile/android/app/mobile.js

@@ -114,6 +114,7 @@ pref("browser.display.remotetabs.timeout", 10);
 /* session history */
 pref("browser.sessionhistory.max_total_viewers", 1);
 pref("browser.sessionhistory.max_entries", 50);
+pref("browser.sessionhistory.contentViewerTimeout", 360);
 
 /* session store */
 pref("browser.sessionstore.resume_session_once", false);