base/third_party/dmg_fp/dtoa_wrapper.cc

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4 //
   5 // The purpose of this file is to supply the macro definintions necessary
   6 // to make third_party/dmg_fp/dtoa.cc threadsafe.
   7 #include "base/lazy_instance.h"
   8 #include "base/logging.h"
   9 #include "base/synchronization/lock.h"
  10
  11 // We need two locks because they're sometimes grabbed at the same time.
  12 // A single lock would lead to an attempted recursive grab.
  13 static base::LazyInstance<base::Lock>::Leaky
  14     dtoa_lock_0 = LAZY_INSTANCE_INITIALIZER;
  15 static base::LazyInstance<base::Lock>::Leaky
  16     dtoa_lock_1 = LAZY_INSTANCE_INITIALIZER;
  17
  18 /*
  19  * This define and the code below is to trigger thread-safe behavior
  20  * in dtoa.cc, per this comment from the file:
  21  *
  22  * #define MULTIPLE_THREADS if the system offers preemptively scheduled
  23  *      multiple threads.  In this case, you must provide (or suitably
  24  *      #define) two locks, acquired by ACQUIRE_DTOA_LOCK(n) and freed
  25  *      by FREE_DTOA_LOCK(n) for n = 0 or 1.  (The second lock, accessed
  26  *      in pow5mult, ensures lazy evaluation of only one copy of high
  27  *      powers of 5; omitting this lock would introduce a small
  28  *      probability of wasting memory, but would otherwise be harmless.)
  29  *      You must also invoke freedtoa(s) to free the value s returned by
  30  *      dtoa.  You may do so whether or not MULTIPLE_THREADS is #defined.
  31  */
  32 #define MULTIPLE_THREADS
  33
  34 inline static void ACQUIRE_DTOA_LOCK(size_t n) {
  35   DCHECK(n < 2);
  36   base::Lock* lock = n == 0 ? dtoa_lock_0.Pointer() : dtoa_lock_1.Pointer();
  37   lock->Acquire();
  38 }
  39
  40 inline static void FREE_DTOA_LOCK(size_t n) {
  41   DCHECK(n < 2);
  42   base::Lock* lock = n == 0 ? dtoa_lock_0.Pointer() : dtoa_lock_1.Pointer();
  43   lock->Release();
  44 }
  45
  46 #include "base/third_party/dmg_fp/dtoa.cc"