Use TLS storage for thread ids in wtf/ThreadingPThreads

third_party/WebKit/Source/wtf/ThreadSpecific.h

 /*
  * Copyright (C) 2008 Apple Inc. All rights reserved.
  * Copyright (C) 2009 Jian Li <jianli@chromium.org>
  * Copyright (C) 2012 Patrick Gansterer <paroga@paroga.com>
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
@@ skipping 27 matching lines @@
  * This semantic discrepancy does not impose any problem because nowhere in
  * WebKit the repeated call bahavior is utilized.
  */
 
 #ifndef WTF_ThreadSpecific_h
 #define WTF_ThreadSpecific_h
 
 #include "wtf/Allocator.h"
 #include "wtf/Noncopyable.h"
 #include "wtf/StdLibExtras.h"
+#include "wtf/Threading.h"

[Charlie Harrison, 2017/01/13 16:38:45]

Remove this.

[Charlie Harrison, 2017/01/13 16:56:55]

Done.

 #include "wtf/WTF.h"
 #include "wtf/WTFExport.h"
 #include "wtf/allocator/PartitionAllocator.h"
 #include "wtf/allocator/Partitions.h"
 
 #if OS(POSIX)
 #include <pthread.h>
 #elif OS(WIN)
 #include <windows.h>
 #endif
@@ skipping 159 matching lines @@
   data->destructor = &ThreadSpecific<T>::destroy;
   TlsSetValue(tlsKeys()[m_index], data);
 }
 
 #else
 #error ThreadSpecific is not implemented for this platform.
 #endif
 
 template <typename T>
 inline void ThreadSpecific<T>::destroy(void* ptr) {
-  // Never call destructors on the main thread.
-  // This is fine because Blink no longer has a graceful shutdown sequence.
-  if (isMainThread())
-    return;
-
   Data* data = static_cast<Data*>(ptr);
 
 #if OS(POSIX)
   // We want get() to keep working while data destructor works, because it can
   // be called indirectly by the destructor.  Some pthreads implementations
   // zero out the pointer before calling destroy(), so we temporarily reset it.
   pthread_setspecific(data->owner->m_key, ptr);
 #endif
 
+  // Never call destructors on the main thread. This is fine because Blink no
+  // longer has a graceful shutdown sequence. Be careful to call this function
+  // (which can be re-entrant) while the pointer is still set, to avoid lazily
+  // allocating WTFThreadData after it is destroyed.
+  if (isMainThread())
+    return;
+
   data->value->~T();
   Partitions::fastFree(data->value);
 
 #if OS(POSIX)
   pthread_setspecific(data->owner->m_key, 0);
 #elif OS(WIN)
   TlsSetValue(tlsKeys()[data->owner->m_index], 0);
 #else
 #error ThreadSpecific is not implemented for this platform.
 #endif
@@ skipping 29 matching lines @@
 template <typename T>
 inline T& ThreadSpecific<T>::operator*() {
   return *operator T*();
 }
 
 }  // namespace WTF
 
 using WTF::ThreadSpecific;
 
 #endif  // WTF_ThreadSpecific_h