Bug 1607739 - Retake thread locks at a consistent point, r=jlast.

Differential Revision: https://phabricator.services.mozilla.com/D59105

--HG--
extra : moz-landing-system : lando

toolkit/recordreplay/ProcessRewind.cpp

@@ -183,6 +183,7 @@ bool ForkProcess() {
   ResetPid();
 
   Thread::RespawnAllThreadsAfterFork();
+  Thread::OperateOnIdleThreadLocks(Thread::OwnedLockState::NeedAcquire);
   Thread::ResumeIdleThreads();
   return false;
 }

toolkit/recordreplay/Thread.cpp

@@ -158,7 +158,6 @@ void Thread::ThreadMain(void* aArgument) {
 
   if (forked) {
     AutoPassThroughThreadEvents pt;
-    thread->ReleaseOrAcquireOwnedLocks(OwnedLockState::NeedAcquire);
     RestoreThreadStack(thread->Id());
   }
 
@@ -554,7 +553,7 @@ void Thread::Wait() {
   thread->SetPassThrough(true);
   int stackSeparator = 0;
   if (!SaveThreadState(thread->Id(), &stackSeparator)) {
-    // We just installed a stack, notify the main thread since it is waiting
+    // We just restored the stack, notify the main thread since it is waiting
     // for all threads to restore their stacks.
     Notify(MainThreadId);
   }

toolkit/recordreplay/ThreadSnapshot.h

@@ -13,10 +13,13 @@
 namespace mozilla {
 namespace recordreplay {
 
-// aStackSeparator is a pointer into the stack. Values shallower than this in
-// the stack will be preserved as they are at the time of the SaveThreadState
-// call, whereas deeper values will be preserved as they are at the point where
-// the main thread saves the remainder of the stack.
+// Save the current thread's registers and the top of the stack, such that the
+// state can be restored later. Returns true if the state was just saved, and
+// false if the state was just restored. aStackSeparator is a pointer into the
+// stack. Values shallower than this in the stack will be preserved as they are
+// at the time of the SaveThreadState call, whereas deeper values will be
+// preserved as they are at the point where the main thread saves the remainder
+// of the stack.
 bool SaveThreadState(size_t aId, int* aStackSeparator);
 
 // Remember the entire stack contents for a thread, after forking.