js/src/vm/SharedScriptDataTableHolder.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
   2  * vim: set ts=8 sts=2 et sw=2 tw=80:
   3  * This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 #ifndef vm_SharedScriptDataTableHolder_h
   8 #define vm_SharedScriptDataTableHolder_h
   9
  10 #include "mozilla/Assertions.h"  // MOZ_ASSERT
  11 #include "mozilla/Maybe.h"       // mozilla::Maybe
  12
  13 #include "threading/Mutex.h"   // js::Mutex
  14 #include "vm/SharedStencil.h"  // js::SharedImmutableScriptDataTable
  15
  16 namespace js {
  17
  18 class AutoLockGlobalScriptData {
  19   static js::Mutex mutex_;
  20
  21  public:
  22   AutoLockGlobalScriptData();
  23   ~AutoLockGlobalScriptData();
  24 };
  25
  26 // A class to provide an access to SharedImmutableScriptDataTable,
  27 // with or without a mutex lock.
  28 //
  29 // js::globalSharedScriptDataTableHolder singleton can be used by any thread,
  30 // and it needs a mutex lock.
  31 //
  32 //   AutoLockGlobalScriptData lock;
  33 //   auto& table = js::globalSharedScriptDataTableHolder::get(lock);
  34 //
  35 // Private SharedScriptDataTableHolder instance can be created for thread-local
  36 // storage, and it can be configured not to require a mutex lock.
  37 //
  38 //   SharedScriptDataTableHolder holder(
  39 //     SharedScriptDataTableHolder::NeedsLock::No);
  40 //   ...
  41 //   auto& table = holder.getWithoutLock();
  42 //
  43 // getMaybeLocked method can be used for both type of instances.
  44 //
  45 //   Maybe<AutoLockGlobalScriptData> lock;
  46 //   auto& table = holder.getMaybeLocked(lock);
  47 //
  48 // Private instance is supposed to be held by the each JSRuntime, including
  49 // both main thread runtime and worker thread runtime, and used in for
  50 // non-helper-thread compilation.
  51 //
  52 // js::globalSharedScriptDataTableHolder singleton is supposed to be used by
  53 // all helper-thread compilation.
  54 class SharedScriptDataTableHolder {
  55   bool needsLock_ = true;
  56   js::SharedImmutableScriptDataTable scriptDataTable_;
  57
  58  public:
  59   enum class NeedsLock { No, Yes };
  60
  61   explicit SharedScriptDataTableHolder(NeedsLock needsLock = NeedsLock::Yes)
  62       : needsLock_(needsLock == NeedsLock::Yes) {}
  63
  64   js::SharedImmutableScriptDataTable& get(
  65       const js::AutoLockGlobalScriptData& lock) {
  66     MOZ_ASSERT(needsLock_);
  67     return scriptDataTable_;
  68   }
  69
  70   js::SharedImmutableScriptDataTable& getWithoutLock() {
  71     MOZ_ASSERT(!needsLock_);
  72     return scriptDataTable_;
  73   }
  74
  75   js::SharedImmutableScriptDataTable& getMaybeLocked(
  76       mozilla::Maybe<js::AutoLockGlobalScriptData>& lock) {
  77     if (needsLock_) {
  78       lock.emplace();
  79     }
  80     return scriptDataTable_;
  81   }
  82 };
  83
  84 extern SharedScriptDataTableHolder globalSharedScriptDataTableHolder;
  85
  86 } /* namespace js */
  87
  88 #endif /* vm_SharedScriptDataTableHolder_h */