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- // -*- Mode: C++; c-basic-offset: 2; indent-tabs-mode: nil -*-
- /* 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
- * 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.
- *
- * ---
- * Author: Sanjay Ghemawat
- */
- #include <config.h>
- #include "base/spinlock.h"
- #ifndef TCMALLOC_SGX
- #include "base/spinlock_internal.h"
- #include "base/sysinfo.h" /* for GetSystemCPUsCount() */
- #endif
- // NOTE on the Lock-state values:
- //
- // kSpinLockFree represents the unlocked state
- // kSpinLockHeld represents the locked state with no waiters
- // kSpinLockSleeper represents the locked state with waiters
- static int adaptive_spin_count = 0;
- const base::LinkerInitialized SpinLock::LINKER_INITIALIZED =
- base::LINKER_INITIALIZED;
- namespace {
- struct SpinLock_InitHelper {
- SpinLock_InitHelper() {
- // On multi-cpu machines, spin for longer before yielding
- // the processor or sleeping. Reduces idle time significantly.
- if (GetSystemCPUsCount() > 1) {
- adaptive_spin_count = 1000;
- }
- }
- };
- // Hook into global constructor execution:
- // We do not do adaptive spinning before that,
- // but nothing lock-intensive should be going on at that time.
- static SpinLock_InitHelper init_helper;
- inline void SpinlockPause(void) {
- #if defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))
- __asm__ __volatile__("rep; nop" : : );
- #endif
- }
- } // unnamed namespace
- // Monitor the lock to see if its value changes within some time
- // period (adaptive_spin_count loop iterations). The last value read
- // from the lock is returned from the method.
- Atomic32 SpinLock::SpinLoop() {
- int c = adaptive_spin_count;
- while (base::subtle::NoBarrier_Load(&lockword_) != kSpinLockFree && --c > 0) {
- SpinlockPause();
- }
- return base::subtle::Acquire_CompareAndSwap(&lockword_, kSpinLockFree,
- kSpinLockSleeper);
- }
- void SpinLock::SlowLock() {
- Atomic32 lock_value = SpinLoop();
-
- #ifndef TCMALLOC_SGX
- int lock_wait_call_count = 0;
- #endif
- while (lock_value != kSpinLockFree) {
- // If the lock is currently held, but not marked as having a sleeper, mark
- // it as having a sleeper.
- if (lock_value == kSpinLockHeld) {
- // Here, just "mark" that the thread is going to sleep. Don't store the
- // lock wait time in the lock as that will cause the current lock
- // owner to think it experienced contention.
- lock_value = base::subtle::Acquire_CompareAndSwap(&lockword_,
- kSpinLockHeld,
- kSpinLockSleeper);
- if (lock_value == kSpinLockHeld) {
- // Successfully transitioned to kSpinLockSleeper. Pass
- // kSpinLockSleeper to the SpinLockDelay routine to properly indicate
- // the last lock_value observed.
- lock_value = kSpinLockSleeper;
- } else if (lock_value == kSpinLockFree) {
- // Lock is free again, so try and acquire it before sleeping. The
- // new lock state will be the number of cycles this thread waited if
- // this thread obtains the lock.
- lock_value = base::subtle::Acquire_CompareAndSwap(&lockword_,
- kSpinLockFree,
- kSpinLockSleeper);
- continue; // skip the delay at the end of the loop
- }
- }
- #ifndef TCMALLOC_SGX /*disable beacuse inside SGX can't do sleep*/
- // Wait for an OS specific delay.
- base::internal::SpinLockDelay(&lockword_, lock_value,
- ++lock_wait_call_count);
- #endif
- // Spin again after returning from the wait routine to give this thread
- // some chance of obtaining the lock.
- lock_value = SpinLoop();
- }
- }
- void SpinLock::SlowUnlock() {
- #ifndef TCMALLOC_SGX
- // wake waiter if necessary
- base::internal::SpinLockWake(&lockword_, false);
- #endif
- }
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