Merge google-perftools r109 (the current contents of third_party/tcmalloc/vendor)

third_party/tcmalloc/chromium/src/base/spinlock_internal.cc

+/* Copyright (c) 2010, 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
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+// The OS-specific header included below must provide two calls:
+// base::internal::SpinLockDelay() and base::internal::SpinLockWake().
+// See spinlock_internal.h for the spec of SpinLockWake().
+
+// void SpinLockDelay(volatile Atomic32 *w, int32 value, int loop)
+// SpinLockDelay() generates an apprproate spin delay on iteration "loop" of a
+// spin loop on location *w, whose previously observed value was "value".
+// SpinLockDelay() may do nothing, may yield the CPU, may sleep a clock tick,
+// or may wait for a delay that can be truncated by a call to SpinlockWake(w).
+// In all cases, it must return in bounded time even if SpinlockWake() is not
+// called.
+
+#include "base/spinlock_internal.h"
+
+#if defined(_WIN32)
+#include "base/spinlock_win32-inl.h"
+#elif defined(__linux__)
+#include "base/spinlock_linux-inl.h"
+#else
+#include "base/spinlock_posix-inl.h"
+#endif
+
+namespace base {
+namespace internal {
+
+// See spinlock_internal.h for spec.
+int32 SpinLockWait(volatile Atomic32 *w, int n,
+                   const SpinLockWaitTransition trans[]) {
+  int32 v;
+  bool done = false;
+  for (int loop = 0; !done; loop++) {
+    v = base::subtle::Acquire_Load(w);
+    int i;
+    for (i = 0; i != n && v != trans[i].from; i++) {
+    }
+    if (i == n) {
+      SpinLockDelay(w, v, loop);     // no matching transition
+    } else if (trans[i].to == v ||   // null transition
+               base::subtle::Acquire_CompareAndSwap(w, v, trans[i].to) == v) {
+      done = trans[i].done;
+    }
+  }
+  return v;
+}
+
+} // namespace internal
+} // namespace base