Bug 1694036: Fix process-start delay and add pref for startup delay r=nika

Differential Revision: https://phabricator.services.mozilla.com/D105878

dom/ipc/PreallocatedProcessManager.cpp

@@ -58,7 +58,7 @@ class PreallocatedProcessManagerImpl final : public nsIObserver {
   void Init();
 
   bool CanAllocate();
-  void AllocateAfterDelay();
+  void AllocateAfterDelay(bool aStartup = false);
   void AllocateOnIdle();
   void AllocateNow();
 
@@ -204,7 +204,7 @@ already_AddRefed<ContentParent> PreallocatedProcessManagerImpl::Take(
 
     // We took a preallocated process. Let's try to start up a new one
     // soon.
-    AllocateOnIdle();
+    AllocateAfterDelay();
     MOZ_LOG(ContentParent::GetLog(), LogLevel::Debug,
             ("Use prealloc process %p", process.get()));
   }
@@ -224,12 +224,14 @@ void PreallocatedProcessManagerImpl::Erase(ContentParent* aParent) {
 
 void PreallocatedProcessManagerImpl::Enable(uint32_t aProcesses) {
   mNumberPreallocs = aProcesses;
+  MOZ_LOG(ContentParent::GetLog(), LogLevel::Debug,
+          ("Enabling preallocation: %u", aProcesses));
   if (mEnabled) {
     return;
   }
 
   mEnabled = true;
-  AllocateAfterDelay();
+  AllocateAfterDelay(/* aStartup */ true);
 }
 
 void PreallocatedProcessManagerImpl::AddBlocker(ContentParent* aParent) {
@@ -267,15 +269,18 @@ bool PreallocatedProcessManagerImpl::CanAllocate() {
           !ContentParent::IsMaxProcessCountReached(DEFAULT_REMOTE_TYPE));
 }
 
-void PreallocatedProcessManagerImpl::AllocateAfterDelay() {
+void PreallocatedProcessManagerImpl::AllocateAfterDelay(bool aStartup) {
   if (!mEnabled) {
     return;
   }
-
+  long delay = aStartup ? StaticPrefs::dom_ipc_processPrelaunch_startupDelayMs()
+                        : StaticPrefs::dom_ipc_processPrelaunch_delayMs();
+  MOZ_LOG(ContentParent::GetLog(), LogLevel::Debug,
+          ("Starting delayed process start, delay=%ld", delay));
   NS_DelayedDispatchToCurrentThread(
       NewRunnableMethod("PreallocatedProcessManagerImpl::AllocateOnIdle", this,
                         &PreallocatedProcessManagerImpl::AllocateOnIdle),
-      StaticPrefs::dom_ipc_processPrelaunch_delayMs());
+      delay);
 }
 
 void PreallocatedProcessManagerImpl::AllocateOnIdle() {
@@ -283,6 +288,8 @@ void PreallocatedProcessManagerImpl::AllocateOnIdle() {
     return;
   }
 
+  MOZ_LOG(ContentParent::GetLog(), LogLevel::Debug,
+          ("Starting process allocate on idle"));
   NS_DispatchToCurrentThreadQueue(
       NewRunnableMethod("PreallocatedProcessManagerImpl::AllocateNow", this,
                         &PreallocatedProcessManagerImpl::AllocateNow),
@@ -290,6 +297,8 @@ void PreallocatedProcessManagerImpl::AllocateOnIdle() {
 }
 
 void PreallocatedProcessManagerImpl::AllocateNow() {
+  MOZ_LOG(ContentParent::GetLog(), LogLevel::Debug,
+          ("Trying to start process now"));
   if (!CanAllocate()) {
     if (mEnabled && !sShutdown && IsEmpty() && sNumBlockers > 0) {
       // If it's too early to allocate a process let's retry later.

modules/libpref/init/StaticPrefList.yaml

@@ -2113,6 +2113,13 @@
   value: 1000
   mirror: always
 
+- name: dom.ipc.processPrelaunch.startupDelayMs
+  type: uint32_t
+# delay starting content processes for a short time after browser start
+# to provide time for the UI to come up
+  value: 1000
+  mirror: always
+
 # Process preallocation cache
 # Only used in fission; in e10s we use 1 always
 - name: dom.ipc.processPrelaunch.fission.number