Squashed 'third_party/gperftools/' content from commit 54505f1
Change-Id: Id02e833828732b0efe7dac722b8485279e67c5fa
git-subtree-dir: third_party/gperftools
git-subtree-split: 54505f1d50c2d1f4676f5e87090b64a117fd980e
diff --git a/src/base/spinlock_internal.cc b/src/base/spinlock_internal.cc
new file mode 100644
index 0000000..e090f9b
--- /dev/null
+++ b/src/base/spinlock_internal.cc
@@ -0,0 +1,122 @@
+// -*- Mode: C++; c-basic-offset: 2; indent-tabs-mode: nil -*-
+/* 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"
+
+// forward declaration for use by spinlock_*-inl.h
+namespace base { namespace internal { static int SuggestedDelayNS(int loop); }}
+
+#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;
+}
+
+// Return a suggested delay in nanoseconds for iteration number "loop"
+static int SuggestedDelayNS(int loop) {
+ // Weak pseudo-random number generator to get some spread between threads
+ // when many are spinning.
+#ifdef BASE_HAS_ATOMIC64
+ static base::subtle::Atomic64 rand;
+ uint64 r = base::subtle::NoBarrier_Load(&rand);
+ r = 0x5deece66dLL * r + 0xb; // numbers from nrand48()
+ base::subtle::NoBarrier_Store(&rand, r);
+
+ r <<= 16; // 48-bit random number now in top 48-bits.
+ if (loop < 0 || loop > 32) { // limit loop to 0..32
+ loop = 32;
+ }
+ // loop>>3 cannot exceed 4 because loop cannot exceed 32.
+ // Select top 20..24 bits of lower 48 bits,
+ // giving approximately 0ms to 16ms.
+ // Mean is exponential in loop for first 32 iterations, then 8ms.
+ // The futex path multiplies this by 16, since we expect explicit wakeups
+ // almost always on that path.
+ return r >> (44 - (loop >> 3));
+#else
+ static Atomic32 rand;
+ uint32 r = base::subtle::NoBarrier_Load(&rand);
+ r = 0x343fd * r + 0x269ec3; // numbers from MSVC++
+ base::subtle::NoBarrier_Store(&rand, r);
+
+ r <<= 1; // 31-bit random number now in top 31-bits.
+ if (loop < 0 || loop > 32) { // limit loop to 0..32
+ loop = 32;
+ }
+ // loop>>3 cannot exceed 4 because loop cannot exceed 32.
+ // Select top 20..24 bits of lower 31 bits,
+ // giving approximately 0ms to 16ms.
+ // Mean is exponential in loop for first 32 iterations, then 8ms.
+ // The futex path multiplies this by 16, since we expect explicit wakeups
+ // almost always on that path.
+ return r >> (12 - (loop >> 3));
+#endif
+}
+
+} // namespace internal
+} // namespace base