dom/promise/PromiseWorkerProxy.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 mozilla_dom_PromiseWorkerProxy_h
   8 #define mozilla_dom_PromiseWorkerProxy_h
   9
  10 #include <cstdint>
  11 #include "js/TypeDecls.h"
  12 #include "mozilla/AlreadyAddRefed.h"
  13 #include "mozilla/Mutex.h"
  14 #include "mozilla/RefPtr.h"
  15 #include "mozilla/dom/Promise.h"
  16 #include "mozilla/dom/PromiseNativeHandler.h"
  17 #include "mozilla/dom/StructuredCloneHolder.h"
  18 #include "nsISupports.h"
  19
  20 struct JSStructuredCloneReader;
  21 struct JSStructuredCloneWriter;
  22
  23 namespace JS {
  24 class CloneDataPolicy;
  25 }  // namespace JS
  26
  27 namespace mozilla {
  28 namespace dom {
  29
  30 class ThreadSafeWorkerRef;
  31 class WorkerPrivate;
  32
  33 // A proxy to (eventually) mirror a resolved/rejected Promise's result from the
  34 // main thread to a Promise on the worker thread.
  35 //
  36 // How to use:
  37 //
  38 //   1. Create a Promise on the worker thread and return it to the content
  39 //      script:
  40 //
  41 //        RefPtr<Promise> promise =
  42 //          Promise::Create(workerPrivate->GlobalScope(), aRv);
  43 //        if (aRv.Failed()) {
  44 //          return nullptr;
  45 //        }
  46 //
  47 //   2. Create a PromiseWorkerProxy wrapping the Promise. If this fails, the
  48 //      worker is shutting down and you should fail the original call. This is
  49 //      only likely to happen in (Gecko-specific) worker onclose handlers.
  50 //
  51 //        RefPtr<PromiseWorkerProxy> proxy =
  52 //          PromiseWorkerProxy::Create(workerPrivate, promise);
  53 //        if (!proxy) {
  54 //          // You may also reject the Promise with an AbortError or similar.
  55 //          return nullptr;
  56 //        }
  57 //
  58 //   3. Dispatch a runnable to the main thread, with a reference to the proxy to
  59 //      perform the main thread operation. PromiseWorkerProxy is thread-safe
  60 //      refcounted.
  61 //
  62 //   4. Return the worker thread promise to the JS caller:
  63 //
  64 //        return promise.forget();
  65 //
  66 //   5. In your main thread runnable Run(), obtain a Promise on
  67 //      the main thread and call its AppendNativeHandler(PromiseNativeHandler*)
  68 //      to bind the PromiseWorkerProxy created at #2.
  69 //
  70 //   4. Then the Promise results returned by ResolvedCallback/RejectedCallback
  71 //      will be dispatched as a WorkerRunnable to the worker thread to
  72 //      resolve/reject the Promise created at #1.
  73 //
  74 // PromiseWorkerProxy can also be used in situations where there is no main
  75 // thread Promise, or where special handling is required on the worker thread
  76 // for promise resolution. Create a PromiseWorkerProxy as in steps 1 to 3
  77 // above. When the main thread is ready to resolve the worker thread promise:
  78 //
  79 //   1. Acquire the mutex before attempting to access the worker private.
  80 //
  81 //        AssertIsOnMainThread();
  82 //        MutexAutoLock lock(proxy->Lock());
  83 //        if (proxy->CleanedUp()) {
  84 //          // Worker has already shut down, can't access worker private.
  85 //          return;
  86 //        }
  87 //
  88 //   2. Dispatch a runnable to the worker. Use GetWorkerPrivate() to acquire the
  89 //      worker.
  90 //
  91 //        RefPtr<FinishTaskWorkerRunnable> runnable =
  92 //          new FinishTaskWorkerRunnable(proxy->GetWorkerPrivate(), proxy,
  93 //                                       result);
  94 //        if (!r->Dispatch()) {
  95 //          // Worker is alive but not Running any more, so the Promise can't
  96 //          // be resolved, give up. The proxy will get Release()d at some
  97 //          // point.
  98 //
  99 //          // Usually do nothing, but you may want to log the fact.
 100 //        }
 101 //
 102 //   3. In the WorkerRunnable's WorkerRun() use WorkerPromise() to access the
 103 //      Promise and resolve/reject it. Then call CleanUp().
 104 //
 105 //        bool
 106 //        WorkerRun(JSContext* aCx, WorkerPrivate* aWorkerPrivate) override
 107 //        {
 108 //          aWorkerPrivate->AssertIsOnWorkerThread();
 109 //          RefPtr<Promise> promise = mProxy->WorkerPromise();
 110 //          promise->MaybeResolve(mResult);
 111 //          mProxy->CleanUp();
 112 //        }
 113 //
 114 // Note: If a PromiseWorkerProxy is not cleaned up by a WorkerRunnable - this
 115 // can happen if the main thread Promise is never fulfilled - it will
 116 // stay alive till the worker reaches a Canceling state, even if all external
 117 // references to it are dropped.
 118
 119 class PromiseWorkerProxy : public PromiseNativeHandler,
 120                            public StructuredCloneHolderBase {
 121   friend class PromiseWorkerProxyRunnable;
 122
 123   NS_DECL_THREADSAFE_ISUPPORTS
 124
 125  public:
 126   typedef JSObject* (*ReadCallbackOp)(JSContext* aCx,
 127                                       JSStructuredCloneReader* aReader,
 128                                       const PromiseWorkerProxy* aProxy,
 129                                       uint32_t aTag, uint32_t aData);
 130   typedef bool (*WriteCallbackOp)(JSContext* aCx,
 131                                   JSStructuredCloneWriter* aWorker,
 132                                   PromiseWorkerProxy* aProxy,
 133                                   JS::HandleObject aObj);
 134
 135   struct PromiseWorkerProxyStructuredCloneCallbacks {
 136     ReadCallbackOp Read;
 137     WriteCallbackOp Write;
 138   };
 139
 140   static already_AddRefed<PromiseWorkerProxy> Create(
 141       WorkerPrivate* aWorkerPrivate, Promise* aWorkerPromise,
 142       const PromiseWorkerProxyStructuredCloneCallbacks* aCallbacks = nullptr);
 143
 144   // Main thread callers must hold Lock() and check CleanUp() before calling
 145   // this. Worker thread callers, this will assert that the proxy has not been
 146   // cleaned up.
 147   WorkerPrivate* GetWorkerPrivate() const;
 148
 149   // This should only be used within WorkerRunnable::WorkerRun() running on the
 150   // worker thread! Do not call this after calling CleanUp().
 151   Promise* WorkerPromise() const;
 152
 153   // Worker thread only. Calling this invalidates several assumptions, so be
 154   // sure this is the last thing you do.
 155   // 1. WorkerPrivate() will no longer return a valid worker.
 156   // 2. WorkerPromise() will crash!
 157   void CleanUp();
 158
 159   Mutex& Lock() { return mCleanUpLock; }
 160
 161   bool CleanedUp() const {
 162     mCleanUpLock.AssertCurrentThreadOwns();
 163     return mCleanedUp;
 164   }
 165
 166   // StructuredCloneHolderBase
 167
 168   JSObject* CustomReadHandler(JSContext* aCx, JSStructuredCloneReader* aReader,
 169                               const JS::CloneDataPolicy& aCloneDataPolicy,
 170                               uint32_t aTag, uint32_t aIndex) override;
 171
 172   bool CustomWriteHandler(JSContext* aCx, JSStructuredCloneWriter* aWriter,
 173                           JS::Handle<JSObject*> aObj,
 174                           bool* aSameProcessScopeRequired) override;
 175
 176  protected:
 177   virtual void ResolvedCallback(JSContext* aCx,
 178                                 JS::Handle<JS::Value> aValue) override;
 179
 180   virtual void RejectedCallback(JSContext* aCx,
 181                                 JS::Handle<JS::Value> aValue) override;
 182
 183  private:
 184   explicit PromiseWorkerProxy(
 185       Promise* aWorkerPromise,
 186       const PromiseWorkerProxyStructuredCloneCallbacks* aCallbacks = nullptr);
 187
 188   virtual ~PromiseWorkerProxy();
 189
 190   // If not called from Create(), be sure to hold Lock().
 191   void CleanProperties();
 192
 193   // Function pointer for calling Promise::{ResolveInternal,RejectInternal}.
 194   typedef void (Promise::*RunCallbackFunc)(JSContext*, JS::Handle<JS::Value>);
 195
 196   void RunCallback(JSContext* aCx, JS::Handle<JS::Value> aValue,
 197                    RunCallbackFunc aFunc);
 198
 199   // Any thread with appropriate checks.
 200   RefPtr<ThreadSafeWorkerRef> mWorkerRef;
 201
 202   // Worker thread only.
 203   RefPtr<Promise> mWorkerPromise;
 204
 205   // Modified on the worker thread.
 206   // It is ok to *read* this without a lock on the worker.
 207   // Main thread must always acquire a lock.
 208   bool mCleanedUp;  // To specify if the cleanUp() has been done.
 209
 210   const PromiseWorkerProxyStructuredCloneCallbacks* mCallbacks;
 211
 212   // Ensure the worker and the main thread won't race to access |mCleanedUp|.
 213   Mutex mCleanUpLock;
 214 };
 215 }  // namespace dom
 216 }  // namespace mozilla
 217
 218 #endif  // mozilla_dom_PromiseWorkerProxy_h