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