Merge r223965 - Unreviewed, rolling out r222945.

https://bugs.webkit.org/show_bug.cgi?id=178818

"It made WasmBench crash" (Requested by saamyjoon on #webkit).

Reverted changeset:

"bmalloc mutex should be adaptive"
https://bugs.webkit.org/show_bug.cgi?id=177839
https://trac.webkit.org/changeset/222945

Source/WTF/ChangeLog

@@ -1,3 +1,16 @@
+2017-10-25  Commit Queue  <commit-queue@webkit.org>
+
+        Unreviewed, rolling out r222945.
+        https://bugs.webkit.org/show_bug.cgi?id=178818
+
+        "It made WasmBench crash" (Requested by saamyjoon on #webkit).
+
+        Reverted changeset:
+
+        "bmalloc mutex should be adaptive"
+        https://bugs.webkit.org/show_bug.cgi?id=177839
+        https://trac.webkit.org/changeset/222945
+
 2017-10-04  Filip Pizlo  <fpizlo@apple.com>
 
         bmalloc mutex should be adaptive

Source/WTF/wtf/LockAlgorithmInlines.h

@@ -33,10 +33,6 @@
 // the lock algorithm slow path without recompiling the world. Right now this should be included in two
 // places (Lock.cpp and JSCell.cpp).
 
-// NOTE: It's a bug to use any memory order other than seq_cst in this code. The cost of seq_cst
-// fencing is negligible on slow paths, so any use of a more relaxed memory model is all risk and no
-// reward.
-
 namespace WTF {
 
 template<typename LockType, LockType isHeldBit, LockType hasParkedBit>

Source/WTF/wtf/WordLock.cpp

@@ -76,10 +76,6 @@ ThreadData* myThreadData()
 
 } // anonymous namespace
 
-// NOTE: It's a bug to use any memory order other than seq_cst in this code. The cost of seq_cst
-// fencing is negligible on slow paths, so any use of a more relaxed memory model is all risk and no
-// reward.
-
 NEVER_INLINE void WordLockBase::lockSlow()
 {
     unsigned spinCount = 0;
@@ -227,8 +223,7 @@ NEVER_INLINE void WordLockBase::unlockSlow()
     ASSERT(currentWordValue & isLockedBit);
     ASSERT(currentWordValue & isQueueLockedBit);
     ThreadData* queueHead = bitwise_cast<ThreadData*>(currentWordValue & ~queueHeadMask);
-    RELEASE_ASSERT(queueHead);
-    RELEASE_ASSERT(queueHead->shouldPark); // This would have been set before the thread was enqueued, so it must still be set now.
+    ASSERT(queueHead);
 
     ThreadData* newQueueHead = queueHead->nextInQueue;
     // Either this was the only thread on the queue, in which case we delete the queue, or there
@@ -261,12 +256,10 @@ NEVER_INLINE void WordLockBase::unlockSlow()
     {
         std::lock_guard<std::mutex> locker(queueHead->parkingLock);
         queueHead->shouldPark = false;
-        // We have to do the notify while still holding the lock, since otherwise, we could try to
-        // do it after the queueHead has destructed. It's impossible for queueHead to destruct
-        // while we hold the lock, since it is either currently in the wait loop or it's before it
-        // so it has to grab the lock before destructing.
-        queueHead->parkingCondition.notify_one();
     }
+    // Doesn't matter if we notify_all() or notify_one() here since the only thread that could be
+    // waiting is queueHead.
+    queueHead->parkingCondition.notify_one();
 
     // The old queue head can now contend for the lock again. We're done!
 }

Source/bmalloc/ChangeLog

@@ -1,3 +1,16 @@
+2017-10-25  Commit Queue  <commit-queue@webkit.org>
+
+        Unreviewed, rolling out r222945.
+        https://bugs.webkit.org/show_bug.cgi?id=178818
+
+        "It made WasmBench crash" (Requested by saamyjoon on #webkit).
+
+        Reverted changeset:
+
+        "bmalloc mutex should be adaptive"
+        https://bugs.webkit.org/show_bug.cgi?id=177839
+        https://trac.webkit.org/changeset/222945
+
 2017-10-23  Zan Dobersek  <zdobersek@igalia.com>
 
         bmalloc::api::tryLargeMemalignVirtual() shouldn't assert on a failed allocation

Source/bmalloc/bmalloc/Algorithm.h

@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2014-2017 Apple Inc. All rights reserved.
+ * Copyright (C) 2014 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
@@ -28,7 +28,6 @@
 
 #include "BAssert.h"
 #include <algorithm>
-#include <atomic>
 #include <cstdint>
 #include <cstddef>
 #include <limits>
@@ -159,24 +158,6 @@ inline constexpr unsigned long log2(unsigned long value)
     return bitCount<unsigned long>() - 1 - __builtin_clzl(value);
 }
 
-// We need a CAS API that isn't the badly designed one from C++.
-template<typename T>
-bool compareExchangeWeak(std::atomic<T>& word, T expected, T desired, std::memory_order order = std::memory_order_seq_cst)
-{
-    // They could have made a sensible CAS API, but they didn't. Sneaky fact: for no good reason, the
-    // C++ API will mutate expected. I think that apologists will say something about how it saves you
-    // reloading the value around the back of your CAS loop, but that's nonsense. The delay along the
-    // back edge of a CAS loop has almost no impact on CAS loop performance. More often than not, we
-    // want to *add* delays to the back edge, not remove them.
-    return word.compare_exchange_weak(expected, desired, order, std::memory_order_relaxed);
-}
-
-template<typename T>
-bool compareExchangeStrong(std::atomic<T>& word, T expected, T desired, std::memory_order order = std::memory_order_seq_cst)
-{
-    return word.compare_exchange_strong(expected, desired, order, std::memory_order_relaxed);
-}
-
 } // namespace bmalloc
 
 #endif // Algorithm_h

Source/bmalloc/bmalloc/PerThread.h

@@ -60,11 +60,11 @@ class PerThread {
     static void destructor(void*);
 };
 
+#if HAVE_PTHREAD_MACHDEP_H
+
 class Cache;
 template<typename T> struct PerThreadStorage;
 
-#if HAVE_PTHREAD_MACHDEP_H
-
 // For now, we only support PerThread<PerHeapKind<Cache>>. We can expand to other types by
 // using more keys.
 template<> struct PerThreadStorage<PerHeapKind<Cache>> {
@@ -82,7 +82,7 @@ template<> struct PerThreadStorage<PerHeapKind<Cache>> {
     }
 };
 
-#endif
+#else
 
 template<typename T> struct PerThreadStorage {
     static bool s_didInitialize;
@@ -112,6 +112,8 @@ template<typename T> bool PerThreadStorage<T>::s_didInitialize;
 template<typename T> pthread_key_t PerThreadStorage<T>::s_key;
 template<typename T> std::once_flag PerThreadStorage<T>::s_onceFlag;
 
+#endif
+
 template<typename T>
 BINLINE T* PerThread<T>::getFastCase()
 {