[heap] Introduce ConcurrentAllocationMutex

Locks the allocation mutex if SupportsConcurrentAllocation() returns
true. Unifies code/condition from multiple usages.

Bug: v8:10315
Change-Id: I684d12284e862df5d68986841e04ff25527422eb
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2352775
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69379}

src/heap/paged-spaces.cc

@@ -433,13 +433,7 @@ void PagedSpace::MakeLinearAllocationAreaIterable() {
 }
 
 size_t PagedSpace::Available() {
-  base::Optional<base::MutexGuard> optional_mutex;
-
-  if (FLAG_concurrent_allocation && identity() == OLD_SPACE &&
-      !is_local_space()) {
-    optional_mutex.emplace(&allocation_mutex_);
-  }
-
+  ConcurrentAllocationMutex guard(this);
   return free_list_->Available();
 }
 
@@ -872,13 +866,7 @@ bool PagedSpace::RefillLabMain(int size_in_bytes, AllocationOrigin origin) {
   VMState<GC> state(heap()->isolate());
   RuntimeCallTimerScope runtime_timer(
       heap()->isolate(), RuntimeCallCounterId::kGC_Custom_SlowAllocateRaw);
-  base::Optional<base::MutexGuard> optional_mutex;
-
-  if (FLAG_concurrent_allocation && origin != AllocationOrigin::kGC &&
-      identity() == OLD_SPACE) {
-    optional_mutex.emplace(&allocation_mutex_);
-  }
-
+  ConcurrentAllocationMutex guard(this);
   return RawRefillLabMain(size_in_bytes, origin);
 }
 

src/heap/paged-spaces.h

@@ -309,6 +309,21 @@ class V8_EXPORT_PRIVATE PagedSpace
   void SetLinearAllocationArea(Address top, Address limit);
 
  private:
+  class ConcurrentAllocationMutex {
+   public:
+    explicit ConcurrentAllocationMutex(PagedSpace* space) {
+      if (space->SupportsConcurrentAllocation()) {
+        guard_.emplace(&space->allocation_mutex_);
+      }
+    }
+
+    base::Optional<base::MutexGuard> guard_;
+  };
+
+  bool SupportsConcurrentAllocation() {
+    return FLAG_concurrent_allocation && !is_local_space();
+  }
+
   // Set space linear allocation area.
   void SetTopAndLimit(Address top, Address limit);
   void DecreaseLimit(Address new_limit);