HeapCompact does not need to look up other threads' states

third_party/WebKit/Source/platform/heap/HeapCompact.cpp

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "platform/heap/HeapCompact.h"
 
 #include "platform/Histogram.h"
 #include "platform/RuntimeEnabledFeatures.h"
 #include "platform/heap/Heap.h"
 #include "platform/heap/SparseHeapBitmap.h"
@@ skipping 285 matching lines @@
   LOG_HEAP_COMPACTION("shouldCompact(): gc=%s count=%zu free=%zu\n",
                       ThreadState::gcReasonString(reason),
                       m_gcCountSinceLastCompaction, m_freeListSize);
   m_gcCountSinceLastCompaction++;
   // It is only safe to compact during non-conservative GCs.
   // TODO: for the main thread, limit this further to only idle GCs.
   if (reason != BlinkGC::IdleGC && reason != BlinkGC::PreciseGC &&
       reason != BlinkGC::ForcedGC)
     return false;
 
-  const ThreadHeap& heap = state->heap();
-  // If any of the participating threads require a stack scan,
-  // do not compact.
-  //
+  // If the GCing thread requires a stack scan, do not compact.
   // Why? Should the stack contain an iterator pointing into its
   // associated backing store, its references wouldn't be
   // correctly relocated.
-  for (ThreadState* state : heap.threads()) {
-    if (state->stackState() == BlinkGC::HeapPointersOnStack) {
-      return false;
-    }
-  }
+  if (state->stackState() == BlinkGC::HeapPointersOnStack)
+    return false;
 
   // Compaction enable rules:
   //  - It's been a while since the last time.
   //  - "Considerable" amount of heap memory is bound up in freelist
   //    allocations. For now, use a fixed limit irrespective of heap
   //    size.
   //
   // As this isn't compacting all arenas, the cost of doing compaction
   // isn't a worry as it will additionally only be done by idle GCs.
   // TODO: add some form of compaction overhead estimate to the marking
@@ skipping 132 matching lines @@
   fixups().addCompactingPage(page);
 }
 
 bool HeapCompact::scheduleCompactionGCForTesting(bool value) {
   bool current = s_forceCompactionGC;
   s_forceCompactionGC = value;
   return current;
 }
 
 }  // namespace blink