Merged third_party/tcmalloc/vendor/src(google-perftools r87) into...

third_party/tcmalloc/chromium/src/base/low_level_alloc.h

 /* Copyright (c) 2006, Google Inc.
  * All rights reserved.
  * 
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  * 
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 54 matching lines @@
     // ATTRIBUTE_SECTION(malloc_hook) for Alloc* and Free
     // are to put all callers of MallocHook::Invoke* in this module
     // into special section,
     // so that MallocHook::GetCallerStackTrace can function accurately.
 
   // Create a new arena.
   // The root metadata for the new arena is allocated in the
   // meta_data_arena; the DefaultArena() can be passed for meta_data_arena.
   // These values may be ored into flags:
   enum {
-    // Calls to Alloc() and Free() will be reported
-    // via the MallocHook interface.
-    // The DefaultArena() has this flag on.
-    // NewArena(flags, DefaultArena()) w/o this bit in 'flags',
-    // on the other hand, will not cause any MallocHook
-    // calls even during the NewArena call itself
-    // (it will in fact use meta_data_arena different from DefaultArena()).
-    kCallMallocHook = 0x0001
+    // Report calls to Alloc() and Free() via the MallocHook interface.
+    // Set in the DefaultArena.
+    kCallMallocHook = 0x0001,
+
+    // Make calls to Alloc(), Free() be async-signal-safe.  Not set in
+    // DefaultArena().
+    kAsyncSignalSafe = 0x0002,
+
+    // When used with DefaultArena(), the NewArena() and DeleteArena() calls
+    // obey the flags given explicitly in the NewArena() call, even if those
+    // flags differ from the settings in DefaultArena().  So the call
+    // NewArena(kAsyncSignalSafe, DefaultArena()) is itself async-signal-safe,
+    // as well as generatating an arena that provides async-signal-safe
+    // Alloc/Free.
   };
   static Arena *NewArena(int32 flags, Arena *meta_data_arena);
 
   // Destroys an arena allocated by NewArena and returns true,
   // provided no allocated blocks remain in the arena.
   // If allocated blocks remain in the arena, does nothing and
   // returns false.
   // It is illegal to attempt to destroy the DefaultArena().
   static bool DeleteArena(Arena *arena);
 
   // The default arena that always exists.
   static Arena *DefaultArena();
 
  private:
   LowLevelAlloc();      // no instances
 };
 
 #endif