third_party/tcmalloc/chromium/src/base/spinlock_linux-inl.h

   1 /* Copyright (c) 2009, Google Inc.
   2  * All rights reserved.
   3  *
   4  * Redistribution and use in source and binary forms, with or without
   5  * modification, are permitted provided that the following conditions are
   6  * met:
   7  *
   8  *     * Redistributions of source code must retain the above copyright
   9  * notice, this list of conditions and the following disclaimer.
  10  *     * Redistributions in binary form must reproduce the above
  11  * copyright notice, this list of conditions and the following disclaimer
  12  * in the documentation and/or other materials provided with the
  13  * distribution.
  14  *     * Neither the name of Google Inc. nor the names of its
  15  * contributors may be used to endorse or promote products derived from
  16  * this software without specific prior written permission.
  17  *
  18  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  19  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  20  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  21  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  22  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  23  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  24  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  25  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  26  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  27  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  28  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  29  *
  30  * ---
  31  * This file is a Linux-specific part of spinlock_internal.cc
  32  */
  33
  34 #include <errno.h>
  35 #include <sched.h>
  36 #include <time.h>
  37 #include <limits.h>
  38 #include "base/linux_syscall_support.h"
  39
  40 #define FUTEX_WAIT 0
  41 #define FUTEX_WAKE 1
  42 #define FUTEX_PRIVATE_FLAG 128
  43
  44 // Note: Instead of making direct system calls that are inlined, we rely
  45 //       on the syscall() function in glibc to do the right thing. This
  46 //       is necessary to make the code compatible with the seccomp sandbox,
  47 //       which needs to be able to find and patch all places where system
  48 //       calls are made. Scanning through and patching glibc is fast, but
  49 //       doing so on the entire Chrome binary would be prohibitively
  50 //       expensive.
  51 //       This is a notable change from the upstream version of tcmalloc,
  52 //       which prefers direct system calls in order to improve compatibility
  53 //       with older toolchains and runtime libraries.
  54
  55 static bool have_futex;
  56 static int futex_private_flag = FUTEX_PRIVATE_FLAG;
  57
  58 namespace {
  59 static struct InitModule {
  60   InitModule() {
  61     int x = 0;
  62     // futexes are ints, so we can use them only when
  63     // that's the same size as the lockword_ in SpinLock.
  64 #ifdef __arm__
  65     // ARM linux doesn't support sys_futex1(void*, int, int, struct timespec*);
  66     have_futex = 0;
  67 #else
  68     have_futex = (sizeof (Atomic32) == sizeof (int) &&
  69                   syscall(__NR_futex, &x, FUTEX_WAKE, 1, 0) >= 0);
  70 #endif
  71     if (have_futex &&
  72         syscall(__NR_futex, &x, FUTEX_WAKE | futex_private_flag, 1, 0) < 0) {
  73       futex_private_flag = 0;
  74     }
  75   }
  76 } init_module;
  77
  78 }  // anonymous namespace
  79
  80
  81 namespace base {
  82 namespace internal {
  83
  84 void SpinLockDelay(volatile Atomic32 *w, int32 value, int loop) {
  85   if (loop != 0) {
  86     int save_errno = errno;
  87     struct timespec tm;
  88     tm.tv_sec = 0;
  89     if (have_futex) {
  90       // Wait between 0-16ms.
  91       tm.tv_nsec = base::internal::SuggestedDelayNS(loop);
  92       // Note: since Unlock() is optimized to not do a compare-and-swap,
  93       // we can't expect explicit wake-ups. Therefore we shouldn't wait too
  94       // long here.
  95       syscall(__NR_futex, reinterpret_cast<int *>(const_cast<Atomic32 *>(w)),
  96                 FUTEX_WAIT | futex_private_flag,
  97                 value, reinterpret_cast<struct kernel_timespec *>(&tm));
  98     } else {
  99       tm.tv_nsec = 2000001;   // above 2ms so linux 2.4 doesn't spin
 100       nanosleep(&tm, NULL);
 101     }
 102     errno = save_errno;
 103   }
 104 }
 105
 106 void SpinLockWake(volatile Atomic32 *w, bool all) {
 107   if (have_futex) {
 108     syscall(__NR_futex, reinterpret_cast<int *>(const_cast<Atomic32 *>(w)),
 109               FUTEX_WAKE | futex_private_flag, 1, 0);
 110   }
 111 }
 112
 113 } // namespace internal
 114 } // namespace base