Bug 1506733 - (part 2) Refactor how the NurseryDecomitter finishes r=jonco

This refactoring is required for the next change.

Differential Revision: https://phabricator.services.mozilla.com/D35590

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

js/src/gc/Nursery.cpp

@@ -108,13 +108,9 @@ void js::NurseryDecommitTask::queueChunk(
   queue = chunk;
 }
 
-Chunk* js::NurseryDecommitTask::popChunk() {
-  AutoLockHelperThreadState lock;
-
+Chunk* js::NurseryDecommitTask::popChunk(
+    const AutoLockHelperThreadState& lock) {
   if (!queue) {
-    // We call setFinishing here while we have the lock that checks for work,
-    // rather than in run's loop.
-    setFinishing(lock);
     return nullptr;
   }
 
@@ -128,8 +124,15 @@ Chunk* js::NurseryDecommitTask::popChunk() {
 void js::NurseryDecommitTask::run() {
   Chunk* chunk;
 
-  while ((chunk = popChunk())) {
-    decommitChunk(chunk);
+  {
+    AutoLockHelperThreadState lock;
+
+    while ((chunk = popChunk(lock))) {
+      AutoUnlockHelperThreadState unlock(lock);
+      decommitChunk(chunk);
+    }
+
+    setFinishing(lock);
   }
 }
 

js/src/gc/Nursery.h

@@ -85,7 +85,7 @@ class NurseryDecommitTask : public GCParallelTaskHelper<NurseryDecommitTask> {
   // Use the next pointers in Chunk::info to form a singly-linked list.
   MainThreadOrGCTaskData<gc::Chunk*> queue;
 
-  gc::Chunk* popChunk();
+  gc::Chunk* popChunk(const AutoLockHelperThreadState& lock);
 };
 
 class TenuringTracer : public JSTracer {