/* Copyright (c) 2009, Google Inc.
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*
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* modification, are permitted provided that the following conditions are
* met:
*
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* 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.
*
* ---
* This file is a Linux-specific part of spinlock_internal.cc
*/
#include <errno.h>
#include <sched.h>
#include <time.h>
#include <limits.h>
#include "base/linux_syscall_support.h"
#define FUTEX_WAIT 0
#define FUTEX_WAKE 1
#define FUTEX_PRIVATE_FLAG 128
// Note: Instead of making direct system calls that are inlined, we rely
// on the syscall() function in glibc to do the right thing. This
// is necessary to make the code compatible with the seccomp sandbox,
// which needs to be able to find and patch all places where system
// calls are made. Scanning through and patching glibc is fast, but
// doing so on the entire Chrome binary would be prohibitively
// expensive.
// This is a notable change from the upstream version of tcmalloc,
// which prefers direct system calls in order to improve compatibility
// with older toolchains and runtime libraries.
static bool have_futex;
static int futex_private_flag = FUTEX_PRIVATE_FLAG;
namespace {
static struct InitModule {
InitModule() {
int x = 0;
// futexes are ints, so we can use them only when
// that's the same size as the lockword_ in SpinLock.
#ifdef __arm__
// ARM linux doesn't support sys_futex1(void*, int, int, struct timespec*);
have_futex = 0;
#else
have_futex = (sizeof (Atomic32) == sizeof (int) &&
syscall(__NR_futex, &x, FUTEX_WAKE, 1, 0) >= 0);
#endif
if (have_futex &&
syscall(__NR_futex, &x, FUTEX_WAKE | futex_private_flag, 1, 0) < 0) {
futex_private_flag = 0;
}
}
} init_module;
} // anonymous namespace
namespace base {
namespace internal {
void SpinLockDelay(volatile Atomic32 *w, int32 value, int loop) {
if (loop != 0) {
int save_errno = errno;
struct timespec tm;
tm.tv_sec = 0;
if (have_futex) {
// Wait between 0-16ms.
tm.tv_nsec = base::internal::SuggestedDelayNS(loop);
// Note: since Unlock() is optimized to not do a compare-and-swap,
// we can't expect explicit wake-ups. Therefore we shouldn't wait too
// long here.
syscall(__NR_futex, reinterpret_cast<int *>(const_cast<Atomic32 *>(w)),
FUTEX_WAIT | futex_private_flag,
value, reinterpret_cast<struct kernel_timespec *>(&tm));
} else {
tm.tv_nsec = 2000001; // above 2ms so linux 2.4 doesn't spin
nanosleep(&tm, NULL);
}
errno = save_errno;
}
}
void SpinLockWake(volatile Atomic32 *w, bool all) {
if (have_futex) {
syscall(__NR_futex, reinterpret_cast<int *>(const_cast<Atomic32 *>(w)),
FUTEX_WAKE | futex_private_flag, 1, 0);
}
}
} // namespace internal
} // namespace base