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 // The naming pattern follows IPC::Channel. 70 static scoped_ptr<SyncChannel> Create( 71 const IPC::ChannelHandle& channel_handle, 72 IPC::Channel::Mode mode, 73 Listener* listener, 74 base::SingleThreadTaskRunner* ipc_task_runner, 75 bool create_pipe_now, 76 base::WaitableEvent* shutdown_event); 77 78 // Creates an uninitialized sync channel. Call ChannelProxy::Init to 79 // initialize the channel. This two-step setup allows message filters to be 80 // added before any messages are sent or received. 81 static scoped_ptr<SyncChannel> Create( 82 Listener* listener, 83 base::SingleThreadTaskRunner* ipc_task_runner, 84 base::WaitableEvent* shutdown_event); 85 86 virtual ~SyncChannel(); 87 88 virtual bool Send(Message* message) OVERRIDE; 89 90 // Sets the dispatch group for this channel, to only allow re-entrant dispatch 91 // of messages to other channels in the same group. 92 // 93 // Normally, any unblocking message coming from any channel can be dispatched 94 // when any (possibly other) channel is blocked on sending a message. This is 95 // needed in some cases to unblock certain loops (e.g. necessary when some 96 // processes share a window hierarchy), but may cause re-entrancy issues in 97 // some cases where such loops are not possible. This flags allows the tagging 98 // of some particular channels to only re-enter in known correct cases. 99 // 100 // Incoming messages on channels belonging to a group that is not 101 // kRestrictDispatchGroup_None will only be dispatched while a sync message is 102 // being sent on a channel of the *same* group. 103 // Incoming messages belonging to the kRestrictDispatchGroup_None group (the 104 // default) will be dispatched in any case. 105 void SetRestrictDispatchChannelGroup(int group); 106 107 protected: 108 class ReceivedSyncMsgQueue; 109 friend class ReceivedSyncMsgQueue; 110 111 // SyncContext holds the per object data for SyncChannel, so that SyncChannel 112 // can be deleted while it's being used in a different thread. See 113 // ChannelProxy::Context for more information. 114 class SyncContext : public Context { 115 public: 116 SyncContext(Listener* listener, 117 base::SingleThreadTaskRunner* ipc_task_runner, 118 base::WaitableEvent* shutdown_event); 119 120 // Adds information about an outgoing sync message to the context so that 121 // we know how to deserialize the reply. 122 void Push(SyncMessage* sync_msg); 123 124 // Cleanly remove the top deserializer (and throw it away). Returns the 125 // result of the Send call for that message. 126 bool Pop(); 127 128 // Returns an event that's set when the send is complete, timed out or the 129 // process shut down. 130 base::WaitableEvent* GetSendDoneEvent(); 131 132 // Returns an event that's set when an incoming message that's not the reply 133 // needs to get dispatched (by calling SyncContext::DispatchMessages). 134 base::WaitableEvent* GetDispatchEvent(); 135 136 void DispatchMessages(); 137 138 // Checks if the given message is blocking the listener thread because of a 139 // synchronous send. If it is, the thread is unblocked and true is 140 // returned. Otherwise the function returns false. 141 bool TryToUnblockListener(const Message* msg); 142 143 // Called on the IPC thread when a sync send that runs a nested message loop 144 // times out. 145 void OnSendTimeout(int message_id); 146 shutdown_event()147 base::WaitableEvent* shutdown_event() { return shutdown_event_; } 148 received_sync_msgs()149 ReceivedSyncMsgQueue* received_sync_msgs() { 150 return received_sync_msgs_.get(); 151 } 152 set_restrict_dispatch_group(int group)153 void set_restrict_dispatch_group(int group) { 154 restrict_dispatch_group_ = group; 155 } 156 restrict_dispatch_group()157 int restrict_dispatch_group() const { 158 return restrict_dispatch_group_; 159 } 160 161 base::WaitableEventWatcher::EventCallback MakeWaitableEventCallback(); 162 163 private: 164 virtual ~SyncContext(); 165 // ChannelProxy methods that we override. 166 167 // Called on the listener thread. 168 virtual void Clear() OVERRIDE; 169 170 // Called on the IPC thread. 171 virtual bool OnMessageReceived(const Message& msg) OVERRIDE; 172 virtual void OnChannelError() OVERRIDE; 173 virtual void OnChannelOpened() OVERRIDE; 174 virtual void OnChannelClosed() OVERRIDE; 175 176 // Cancels all pending Send calls. 177 void CancelPendingSends(); 178 179 void OnWaitableEventSignaled(base::WaitableEvent* event); 180 181 typedef std::deque<PendingSyncMsg> PendingSyncMessageQueue; 182 PendingSyncMessageQueue deserializers_; 183 base::Lock deserializers_lock_; 184 185 scoped_refptr<ReceivedSyncMsgQueue> received_sync_msgs_; 186 187 base::WaitableEvent* shutdown_event_; 188 base::WaitableEventWatcher shutdown_watcher_; 189 base::WaitableEventWatcher::EventCallback shutdown_watcher_callback_; 190 int restrict_dispatch_group_; 191 }; 192 193 private: 194 SyncChannel(Listener* listener, 195 base::SingleThreadTaskRunner* ipc_task_runner, 196 base::WaitableEvent* shutdown_event); 197 198 void OnWaitableEventSignaled(base::WaitableEvent* arg); 199 sync_context()200 SyncContext* sync_context() { 201 return reinterpret_cast<SyncContext*>(context()); 202 } 203 204 // Both these functions wait for a reply, timeout or process shutdown. The 205 // latter one also runs a nested message loop in the meantime. 206 static void WaitForReply( 207 SyncContext* context, base::WaitableEvent* pump_messages_event); 208 209 // Runs a nested message loop until a reply arrives, times out, or the process 210 // shuts down. 211 static void WaitForReplyWithNestedMessageLoop(SyncContext* context); 212 213 // Starts the dispatch watcher. 214 void StartWatching(); 215 216 // Used to signal events between the IPC and listener threads. 217 base::WaitableEventWatcher dispatch_watcher_; 218 base::WaitableEventWatcher::EventCallback dispatch_watcher_callback_; 219 220 DISALLOW_COPY_AND_ASSIGN(SyncChannel); 221 }; 222 223 } // namespace IPC 224 225 #endif // IPC_IPC_SYNC_CHANNEL_H_ 226