gecko/ipc/glue/RPCChannel.h

199 lines
7.1 KiB
C++

/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*-
* vim: sw=4 ts=4 et :
* ***** BEGIN LICENSE BLOCK *****
* Version: MPL 1.1/GPL 2.0/LGPL 2.1
*
* The contents of this file are subject to the Mozilla Public License Version
* 1.1 (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
* http://www.mozilla.org/MPL/
*
* Software distributed under the License is distributed on an "AS IS" basis,
* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
* for the specific language governing rights and limitations under the
* License.
*
* The Original Code is Mozilla Plugin App.
*
* The Initial Developer of the Original Code is
* Chris Jones <jones.chris.g@gmail.com>
* Portions created by the Initial Developer are Copyright (C) 2009
* the Initial Developer. All Rights Reserved.
*
* Contributor(s):
*
* Alternatively, the contents of this file may be used under the terms of
* either the GNU General Public License Version 2 or later (the "GPL"), or
* the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
* in which case the provisions of the GPL or the LGPL are applicable instead
* of those above. If you wish to allow use of your version of this file only
* under the terms of either the GPL or the LGPL, and not to allow others to
* use your version of this file under the terms of the MPL, indicate your
* decision by deleting the provisions above and replace them with the notice
* and other provisions required by the GPL or the LGPL. If you do not delete
* the provisions above, a recipient may use your version of this file under
* the terms of any one of the MPL, the GPL or the LGPL.
*
* ***** END LICENSE BLOCK ***** */
#ifndef ipc_glue_RPCChannel_h
#define ipc_glue_RPCChannel_h 1
// FIXME/cjones probably shouldn't depend on STL
#include <queue>
#include <stack>
#include "mozilla/ipc/SyncChannel.h"
namespace mozilla {
namespace ipc {
//-----------------------------------------------------------------------------
class RPCChannel : public SyncChannel
{
public:
class /*NS_INTERFACE_CLASS*/ RPCListener :
public SyncChannel::SyncListener
{
public:
virtual ~RPCListener() { }
virtual void OnChannelClose() = 0;
virtual void OnChannelError() = 0;
virtual Result OnMessageReceived(const Message& aMessage) = 0;
virtual Result OnMessageReceived(const Message& aMessage,
Message*& aReply) = 0;
virtual Result OnCallReceived(const Message& aMessage,
Message*& aReply) = 0;
};
// What happens if RPC calls race?
enum RacyRPCPolicy {
RRPError,
RRPChildWins,
RRPParentWins
};
RPCChannel(RPCListener* aListener, RacyRPCPolicy aPolicy=RRPChildWins);
virtual ~RPCChannel();
// Make an RPC to the other side of the channel
bool Call(Message* msg, Message* reply);
// Override the SyncChannel handler so we can dispatch RPC
// messages. Called on the IO thread only.
NS_OVERRIDE virtual void OnMessageReceived(const Message& msg);
NS_OVERRIDE virtual void OnChannelError();
private:
// Called on worker thread only
void MaybeProcessDeferredIncall();
void EnqueuePendingMessages();
void OnMaybeDequeueOne();
void Incall(const Message& call, size_t stackDepth);
void DispatchIncall(const Message& call);
// Called from both threads
size_t StackDepth() {
mMutex.AssertCurrentThreadOwns();
return mStack.size();
}
void DebugAbort(const char* file, int line, const char* cond,
const char* why,
const char* type="rpc", bool reply=false);
//
// Queue of all incoming messages, except for replies to sync
// messages, which are delivered directly to the SyncChannel
// through its mRecvd member.
//
// If both this side and the other side are functioning correctly,
// the queue can only be in certain configurations. Let
//
// |A<| be an async in-message,
// |S<| be a sync in-message,
// |C<| be an RPC in-call,
// |R<| be an RPC reply.
//
// The queue can only match this configuration
//
// A<* (S< | C< | R< (?{mStack.size() == 1} A<* (S< | C<)))
//
// The other side can send as many async messages |A<*| as it
// wants before sending us a blocking message.
//
// The first case is |S<|, a sync in-msg. The other side must be
// blocked, and thus can't send us any more messages until we
// process the sync in-msg.
//
// The second case is |C<|, an RPC in-call; the other side must be
// blocked. (There's a subtlety here: this in-call might have
// raced with an out-call, but we detect that with the mechanism
// below, |mRemoteStackDepth|, and races don't matter to the
// queue.)
//
// Final case, the other side replied to our most recent out-call
// |R<|. If that was the *only* out-call on our stack,
// |?{mStack.size() == 1}|, then other side "finished with us,"
// and went back to its own business. That business might have
// included sending any number of async message |A<*| until
// sending a blocking message |(S< | C<)|. If we had more than
// one RPC call on our stack, the other side *better* not have
// sent us another blocking message, because it's blocked on a
// reply from us.
//
std::queue<Message> mPending;
//
// Stack of all the RPC out-calls on which this RPCChannel is
// awaiting a response.
//
std::stack<Message> mStack;
//
// Stack of RPC in-calls that were deferred because of race
// conditions.
//
std::stack<Message> mDeferred;
//
// This is what we think the RPC stack depth is on the "other
// side" of this RPC channel. We maintain this variable so that
// we can detect racy RPC calls. With each RPC out-call sent, we
// send along what *we* think the stack depth of the remote side
// is *before* it will receive the RPC call.
//
// After sending the out-call, our stack depth is "incremented"
// by pushing that pending message onto mPending.
//
// Then when processing an in-call |c|, it must be true that
//
// mStack.size() == c.remoteDepth
//
// i.e., my depth is actually the same as what the other side
// thought it was when it sent in-call |c|. If this fails to
// hold, we have detected racy RPC calls.
//
// We then increment mRemoteStackDepth *just before* processing
// the in-call, since we know the other side is waiting on it, and
// decrement it *just after* finishing processing that in-call,
// since our response will pop the top of the other side's
// |mPending|.
//
// One nice aspect of this race detection is that it is symmetric;
// if one side detects a race, then the other side must also
// detect the same race.
//
size_t mRemoteStackDepthGuess;
RacyRPCPolicy mRacePolicy;
};
} // namespace ipc
} // namespace mozilla
#endif // ifndef ipc_glue_RPCChannel_h