ipc/ipc_sync_channel.h

   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 #ifndef IPC_IPC_SYNC_CHANNEL_H_
   6 #define IPC_IPC_SYNC_CHANNEL_H_
   7
   8 #include <string>
   9 #include <deque>
  10
  11 #include "base/basictypes.h"
  12 #include "base/memory/ref_counted.h"
  13 #include "base/synchronization/lock.h"
  14 #include "base/synchronization/waitable_event_watcher.h"
  15 #include "ipc/ipc_channel_handle.h"
  16 #include "ipc/ipc_channel_proxy.h"
  17 #include "ipc/ipc_sync_message.h"
  18
  19 namespace base {
  20 class WaitableEvent;
  21 };
  22
  23 namespace IPC {
  24
  25 class SyncMessage;
  26 class ChannelFactory;
  27
  28 // This is similar to ChannelProxy, with the added feature of supporting sending
  29 // synchronous messages.
  30 //
  31 // Overview of how the sync channel works
  32 // --------------------------------------
  33 // When the sending thread sends a synchronous message, we create a bunch
  34 // of tracking info (created in Send, stored in the PendingSyncMsg
  35 // structure) associated with the message that we identify by the unique
  36 // "MessageId" on the SyncMessage. Among the things we save is the
  37 // "Deserializer" which is provided by the sync message. This object is in
  38 // charge of reading the parameters from the reply message and putting them in
  39 // the output variables provided by its caller.
  40 //
  41 // The info gets stashed in a queue since we could have a nested stack of sync
  42 // messages (each side could send sync messages in response to sync messages,
  43 // so it works like calling a function). The message is sent to the I/O thread
  44 // for dispatch and the original thread blocks waiting for the reply.
  45 //
  46 // SyncContext maintains the queue in a threadsafe way and listens for replies
  47 // on the I/O thread. When a reply comes in that matches one of the messages
  48 // it's looking for (using the unique message ID), it will execute the
  49 // deserializer stashed from before, and unblock the original thread.
  50 //
  51 //
  52 // Significant complexity results from the fact that messages are still coming
  53 // in while the original thread is blocked. Normal async messages are queued
  54 // and dispatched after the blocking call is complete. Sync messages must
  55 // be dispatched in a reentrant manner to avoid deadlock.
  56 //
  57 //
  58 // Note that care must be taken that the lifetime of the ipc_thread argument
  59 // is more than this object.  If the message loop goes away while this object
  60 // is running and it's used to send a message, then it will use the invalid
  61 // message loop pointer to proxy it to the ipc thread.
  62 class IPC_EXPORT SyncChannel : public ChannelProxy {
  63  public:
  64   enum RestrictDispatchGroup {
  65     kRestrictDispatchGroup_None = 0,
  66   };
  67
  68   // Creates and initializes a sync channel. If create_pipe_now is specified,
  69   // the channel will be initialized synchronously.
  70   // The naming pattern follows IPC::Channel.
  71   static scoped_ptr<SyncChannel> Create(
  72       const IPC::ChannelHandle& channel_handle,
  73       IPC::Channel::Mode mode,
  74       Listener* listener,
  75       const scoped_refptr<base::SingleThreadTaskRunner>& ipc_task_runner,
  76       bool create_pipe_now,
  77       base::WaitableEvent* shutdown_event);
  78
  79   static scoped_ptr<SyncChannel> Create(
  80       scoped_ptr<ChannelFactory> factory,
  81       Listener* listener,
  82       const scoped_refptr<base::SingleThreadTaskRunner>& ipc_task_runner,
  83       bool create_pipe_now,
  84       base::WaitableEvent* shutdown_event);
  85
  86   // Creates an uninitialized sync channel. Call ChannelProxy::Init to
  87   // initialize the channel. This two-step setup allows message filters to be
  88   // added before any messages are sent or received.
  89   static scoped_ptr<SyncChannel> Create(
  90       Listener* listener,
  91       const scoped_refptr<base::SingleThreadTaskRunner>& ipc_task_runner,
  92       base::WaitableEvent* shutdown_event);
  93
  94   ~SyncChannel() override;
  95
  96   bool Send(Message* message) override;
  97
  98   // Sets the dispatch group for this channel, to only allow re-entrant dispatch
  99   // of messages to other channels in the same group.
 100   //
 101   // Normally, any unblocking message coming from any channel can be dispatched
 102   // when any (possibly other) channel is blocked on sending a message. This is
 103   // needed in some cases to unblock certain loops (e.g. necessary when some
 104   // processes share a window hierarchy), but may cause re-entrancy issues in
 105   // some cases where such loops are not possible. This flags allows the tagging
 106   // of some particular channels to only re-enter in known correct cases.
 107   //
 108   // Incoming messages on channels belonging to a group that is not
 109   // kRestrictDispatchGroup_None will only be dispatched while a sync message is
 110   // being sent on a channel of the *same* group.
 111   // Incoming messages belonging to the kRestrictDispatchGroup_None group (the
 112   // default) will be dispatched in any case.
 113   void SetRestrictDispatchChannelGroup(int group);
 114
 115  protected:
 116   class ReceivedSyncMsgQueue;
 117   friend class ReceivedSyncMsgQueue;
 118
 119   // SyncContext holds the per object data for SyncChannel, so that SyncChannel
 120   // can be deleted while it's being used in a different thread.  See
 121   // ChannelProxy::Context for more information.
 122   class SyncContext : public Context {
 123    public:
 124     SyncContext(
 125         Listener* listener,
 126         const scoped_refptr<base::SingleThreadTaskRunner>& ipc_task_runner,
 127         base::WaitableEvent* shutdown_event);
 128
 129     // Adds information about an outgoing sync message to the context so that
 130     // we know how to deserialize the reply.
 131     void Push(SyncMessage* sync_msg);
 132
 133     // Cleanly remove the top deserializer (and throw it away).  Returns the
 134     // result of the Send call for that message.
 135     bool Pop();
 136
 137     // Returns an event that's set when the send is complete, timed out or the
 138     // process shut down.
 139     base::WaitableEvent* GetSendDoneEvent();
 140
 141     // Returns an event that's set when an incoming message that's not the reply
 142     // needs to get dispatched (by calling SyncContext::DispatchMessages).
 143     base::WaitableEvent* GetDispatchEvent();
 144
 145     void DispatchMessages();
 146
 147     // Checks if the given message is blocking the listener thread because of a
 148     // synchronous send.  If it is, the thread is unblocked and true is
 149     // returned. Otherwise the function returns false.
 150     bool TryToUnblockListener(const Message* msg);
 151
 152     // Called on the IPC thread when a sync send that runs a nested message loop
 153     // times out.
 154     void OnSendTimeout(int message_id);
 155
 156     base::WaitableEvent* shutdown_event() { return shutdown_event_; }
 157
 158     ReceivedSyncMsgQueue* received_sync_msgs() {
 159       return received_sync_msgs_.get();
 160     }
 161
 162     void set_restrict_dispatch_group(int group) {
 163       restrict_dispatch_group_ = group;
 164     }
 165
 166     int restrict_dispatch_group() const {
 167       return restrict_dispatch_group_;
 168     }
 169
 170     base::WaitableEventWatcher::EventCallback MakeWaitableEventCallback();
 171
 172    private:
 173     ~SyncContext() override;
 174     // ChannelProxy methods that we override.
 175
 176     // Called on the listener thread.
 177     void Clear() override;
 178
 179     // Called on the IPC thread.
 180     bool OnMessageReceived(const Message& msg) override;
 181     void OnChannelError() override;
 182     void OnChannelOpened() override;
 183     void OnChannelClosed() override;
 184
 185     // Cancels all pending Send calls.
 186     void CancelPendingSends();
 187
 188     void OnWaitableEventSignaled(base::WaitableEvent* event);
 189
 190     typedef std::deque<PendingSyncMsg> PendingSyncMessageQueue;
 191     PendingSyncMessageQueue deserializers_;
 192     base::Lock deserializers_lock_;
 193
 194     scoped_refptr<ReceivedSyncMsgQueue> received_sync_msgs_;
 195
 196     base::WaitableEvent* shutdown_event_;
 197     base::WaitableEventWatcher shutdown_watcher_;
 198     base::WaitableEventWatcher::EventCallback shutdown_watcher_callback_;
 199     int restrict_dispatch_group_;
 200   };
 201
 202  private:
 203   SyncChannel(
 204       Listener* listener,
 205       const scoped_refptr<base::SingleThreadTaskRunner>& ipc_task_runner,
 206       base::WaitableEvent* shutdown_event);
 207
 208   void OnWaitableEventSignaled(base::WaitableEvent* arg);
 209
 210   SyncContext* sync_context() {
 211     return reinterpret_cast<SyncContext*>(context());
 212   }
 213
 214   // Both these functions wait for a reply, timeout or process shutdown.  The
 215   // latter one also runs a nested message loop in the meantime.
 216   static void WaitForReply(
 217       SyncContext* context, base::WaitableEvent* pump_messages_event);
 218
 219   // Runs a nested message loop until a reply arrives, times out, or the process
 220   // shuts down.
 221   static void WaitForReplyWithNestedMessageLoop(SyncContext* context);
 222
 223   // Starts the dispatch watcher.
 224   void StartWatching();
 225
 226   // Used to signal events between the IPC and listener threads.
 227   base::WaitableEventWatcher dispatch_watcher_;
 228   base::WaitableEventWatcher::EventCallback dispatch_watcher_callback_;
 229
 230   DISALLOW_COPY_AND_ASSIGN(SyncChannel);
 231 };
 232
 233 }  // namespace IPC
 234
 235 #endif  // IPC_IPC_SYNC_CHANNEL_H_