gecko/ipc/glue/RPCChannel.cpp

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/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*-
* vim: sw=4 ts=4 et :
*/
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/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
#include "mozilla/ipc/RPCChannel.h"
#include "mozilla/ipc/ProtocolUtils.h"
#include "nsDebug.h"
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#include "nsTraceRefcnt.h"
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#define RPC_ASSERT(_cond, ...) \
do { \
if (!(_cond)) \
DebugAbort(__FILE__, __LINE__, #_cond,## __VA_ARGS__); \
} while (0)
using mozilla::MonitorAutoLock;
using mozilla::MonitorAutoUnlock;
template<>
struct RunnableMethodTraits<mozilla::ipc::RPCChannel>
{
static void RetainCallee(mozilla::ipc::RPCChannel* obj) { }
static void ReleaseCallee(mozilla::ipc::RPCChannel* obj) { }
};
namespace
{
// Async (from the sending side's perspective)
class BlockChildMessage : public IPC::Message
{
public:
enum { ID = BLOCK_CHILD_MESSAGE_TYPE };
BlockChildMessage() :
Message(MSG_ROUTING_NONE, ID, IPC::Message::PRIORITY_NORMAL)
{ }
};
// Async
class UnblockChildMessage : public IPC::Message
{
public:
enum { ID = UNBLOCK_CHILD_MESSAGE_TYPE };
UnblockChildMessage() :
Message(MSG_ROUTING_NONE, ID, IPC::Message::PRIORITY_NORMAL)
{ }
};
} // namespace <anon>
namespace mozilla {
namespace ipc {
RPCChannel::RPCChannel(RPCListener* aListener)
: SyncChannel(aListener),
mPending(),
mStack(),
mOutOfTurnReplies(),
mDeferred(),
mRemoteStackDepthGuess(0),
mBlockedOnParent(false),
mSawRPCOutMsg(false)
{
MOZ_COUNT_CTOR(RPCChannel);
mDequeueOneTask = new RefCountedTask(NewRunnableMethod(
this,
&RPCChannel::OnMaybeDequeueOne));
}
RPCChannel::~RPCChannel()
{
MOZ_COUNT_DTOR(RPCChannel);
RPC_ASSERT(mCxxStackFrames.empty(), "mismatched CxxStackFrame ctor/dtors");
}
void
RPCChannel::Clear()
{
mDequeueOneTask->Cancel();
AsyncChannel::Clear();
}
bool
RPCChannel::EventOccurred() const
{
AssertWorkerThread();
mMonitor->AssertCurrentThreadOwns();
RPC_ASSERT(StackDepth() > 0, "not in wait loop");
return (!Connected() ||
!mPending.empty() ||
(!mOutOfTurnReplies.empty() &&
mOutOfTurnReplies.find(mStack.top().seqno())
!= mOutOfTurnReplies.end()));
}
bool
RPCChannel::Send(Message* msg)
{
Message copy = *msg;
CxxStackFrame f(*this, OUT_MESSAGE, &copy);
return AsyncChannel::Send(msg);
}
bool
RPCChannel::Send(Message* msg, Message* reply)
{
Message copy = *msg;
CxxStackFrame f(*this, OUT_MESSAGE, &copy);
return SyncChannel::Send(msg, reply);
}
bool
RPCChannel::Call(Message* _msg, Message* reply)
{
nsAutoPtr<Message> msg(_msg);
AssertWorkerThread();
mMonitor->AssertNotCurrentThreadOwns();
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RPC_ASSERT(!ProcessingSyncMessage(),
"violation of sync handler invariant");
RPC_ASSERT(msg->is_rpc(), "can only Call() RPC messages here");
#ifdef OS_WIN
SyncStackFrame frame(this, true);
#endif
Message copy = *msg;
CxxStackFrame f(*this, OUT_MESSAGE, &copy);
MonitorAutoLock lock(*mMonitor);
if (!Connected()) {
ReportConnectionError("RPCChannel");
return false;
}
msg->set_seqno(NextSeqno());
msg->set_rpc_remote_stack_depth_guess(mRemoteStackDepthGuess);
msg->set_rpc_local_stack_depth(1 + StackDepth());
mStack.push(*msg);
mLink->SendMessage(msg.forget());
while (1) {
// if a handler invoked by *Dispatch*() spun a nested event
// loop, and the connection was broken during that loop, we
// might have already processed the OnError event. if so,
// trying another loop iteration will be futile because
// channel state will have been cleared
if (!Connected()) {
ReportConnectionError("RPCChannel");
return false;
}
// now might be the time to process a message deferred because
// of race resolution
MaybeUndeferIncall();
// here we're waiting for something to happen. see long
// comment about the queue in RPCChannel.h
while (!EventOccurred()) {
bool maybeTimedOut = !RPCChannel::WaitForNotify();
if (EventOccurred() ||
// we might have received a "subtly deferred" message
// in a nested loop that it's now time to process
(!maybeTimedOut &&
(!mDeferred.empty() || !mOutOfTurnReplies.empty())))
break;
if (maybeTimedOut && !ShouldContinueFromTimeout())
return false;
}
if (!Connected()) {
ReportConnectionError("RPCChannel");
return false;
}
Message recvd;
MessageMap::iterator it;
if (!mOutOfTurnReplies.empty() &&
((it = mOutOfTurnReplies.find(mStack.top().seqno())) !=
mOutOfTurnReplies.end())) {
recvd = it->second;
mOutOfTurnReplies.erase(it);
}
else if (!mPending.empty()) {
recvd = mPending.front();
mPending.pop_front();
}
else {
// because of subtleties with nested event loops, it's
// possible that we got here and nothing happened. or, we
// might have a deferred in-call that needs to be
// processed. either way, we won't break the inner while
// loop again until something new happens.
continue;
}
if (!recvd.is_sync() && !recvd.is_rpc()) {
MonitorAutoUnlock unlock(*mMonitor);
CxxStackFrame f(*this, IN_MESSAGE, &recvd);
AsyncChannel::OnDispatchMessage(recvd);
continue;
}
if (recvd.is_sync()) {
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RPC_ASSERT(mPending.empty(),
"other side should have been blocked");
MonitorAutoUnlock unlock(*mMonitor);
CxxStackFrame f(*this, IN_MESSAGE, &recvd);
SyncChannel::OnDispatchMessage(recvd);
continue;
}
RPC_ASSERT(recvd.is_rpc(), "wtf???");
if (recvd.is_reply()) {
RPC_ASSERT(0 < mStack.size(), "invalid RPC stack");
const Message& outcall = mStack.top();
// in the parent, seqno's increase from 0, and in the
// child, they decrease from 0
if ((!mChild && recvd.seqno() < outcall.seqno()) ||
(mChild && recvd.seqno() > outcall.seqno())) {
mOutOfTurnReplies[recvd.seqno()] = recvd;
continue;
}
// FIXME/cjones: handle error
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RPC_ASSERT(
recvd.is_reply_error() ||
(recvd.type() == (outcall.type()+1) &&
recvd.seqno() == outcall.seqno()),
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"somebody's misbehavin'", "rpc", true);
// we received a reply to our most recent outstanding
// call. pop this frame and return the reply
mStack.pop();
bool isError = recvd.is_reply_error();
if (!isError) {
*reply = recvd;
}
if (0 == StackDepth()) {
RPC_ASSERT(
mOutOfTurnReplies.empty(),
"still have pending replies with no pending out-calls",
"rpc", true);
}
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// finished with this RPC stack frame
return !isError;
}
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// in-call. process in a new stack frame.
// "snapshot" the current stack depth while we own the Monitor
size_t stackDepth = StackDepth();
{
MonitorAutoUnlock unlock(*mMonitor);
// someone called in to us from the other side. handle the call
CxxStackFrame f(*this, IN_MESSAGE, &recvd);
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Incall(recvd, stackDepth);
// FIXME/cjones: error handling
}
}
return true;
}
void
RPCChannel::MaybeUndeferIncall()
{
AssertWorkerThread();
mMonitor->AssertCurrentThreadOwns();
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if (mDeferred.empty())
return;
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size_t stackDepth = StackDepth();
// the other side can only *under*-estimate our actual stack depth
RPC_ASSERT(mDeferred.top().rpc_remote_stack_depth_guess() <= stackDepth,
"fatal logic error");
if (mDeferred.top().rpc_remote_stack_depth_guess() < RemoteViewOfStackDepth(stackDepth))
return;
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// maybe time to process this message
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Message call = mDeferred.top();
mDeferred.pop();
// fix up fudge factor we added to account for race
RPC_ASSERT(0 < mRemoteStackDepthGuess, "fatal logic error");
--mRemoteStackDepthGuess;
mPending.push_back(call);
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}
void
RPCChannel::EnqueuePendingMessages()
{
AssertWorkerThread();
mMonitor->AssertCurrentThreadOwns();
MaybeUndeferIncall();
for (size_t i = 0; i < mDeferred.size(); ++i)
mWorkerLoop->PostTask(
FROM_HERE,
new DequeueTask(mDequeueOneTask));
// XXX performance tuning knob: could process all or k pending
// messages here, rather than enqueuing for later processing
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for (size_t i = 0; i < mPending.size(); ++i)
mWorkerLoop->PostTask(
FROM_HERE,
new DequeueTask(mDequeueOneTask));
}
void
RPCChannel::FlushPendingRPCQueue()
{
AssertWorkerThread();
mMonitor->AssertNotCurrentThreadOwns();
{
MonitorAutoLock lock(*mMonitor);
if (mDeferred.empty()) {
if (mPending.empty())
return;
const Message& last = mPending.back();
if (!last.is_rpc() || last.is_reply())
return;
}
}
while (OnMaybeDequeueOne());
}
bool
RPCChannel::OnMaybeDequeueOne()
{
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// XXX performance tuning knob: could process all or k pending
// messages here
AssertWorkerThread();
mMonitor->AssertNotCurrentThreadOwns();
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Message recvd;
{
MonitorAutoLock lock(*mMonitor);
if (!Connected()) {
ReportConnectionError("RPCChannel");
return false;
}
if (!mDeferred.empty())
MaybeUndeferIncall();
if (mPending.empty())
return false;
recvd = mPending.front();
mPending.pop_front();
}
if (IsOnCxxStack() && recvd.is_rpc() && recvd.is_reply()) {
// We probably just received a reply in a nested loop for an
// RPC call sent before entering that loop.
mOutOfTurnReplies[recvd.seqno()] = recvd;
return false;
}
CxxStackFrame f(*this, IN_MESSAGE, &recvd);
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if (recvd.is_rpc())
Incall(recvd, 0);
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else if (recvd.is_sync())
SyncChannel::OnDispatchMessage(recvd);
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else
AsyncChannel::OnDispatchMessage(recvd);
return true;
}
size_t
RPCChannel::RemoteViewOfStackDepth(size_t stackDepth) const
{
AssertWorkerThread();
return stackDepth - mOutOfTurnReplies.size();
}
void
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RPCChannel::Incall(const Message& call, size_t stackDepth)
{
AssertWorkerThread();
mMonitor->AssertNotCurrentThreadOwns();
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RPC_ASSERT(call.is_rpc() && !call.is_reply(), "wrong message type");
// Race detection: see the long comment near
// mRemoteStackDepthGuess in RPCChannel.h. "Remote" stack depth
// means our side, and "local" means other side.
if (call.rpc_remote_stack_depth_guess() != RemoteViewOfStackDepth(stackDepth)) {
// RPC in-calls have raced.
// the "winner", if there is one, gets to defer processing of
// the other side's in-call
bool defer;
const char* winner;
switch (Listener()->MediateRPCRace(mChild ? call : mStack.top(),
mChild ? mStack.top() : call)) {
case RRPChildWins:
winner = "child";
defer = mChild;
break;
case RRPParentWins:
winner = "parent";
defer = !mChild;
break;
case RRPError:
NS_RUNTIMEABORT("NYI: 'Error' RPC race policy");
return;
default:
NS_RUNTIMEABORT("not reached");
return;
}
if (LoggingEnabled()) {
printf_stderr(" (%s: %s won, so we're%sdeferring)\n",
mChild ? "child" : "parent", winner,
defer ? " " : " not ");
}
if (defer) {
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// we now know the other side's stack has one more frame
// than we thought
++mRemoteStackDepthGuess; // decremented in MaybeProcessDeferred()
mDeferred.push(call);
return;
}
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// we "lost" and need to process the other side's in-call.
// don't need to fix up the mRemoteStackDepthGuess here,
// because we're just about to increment it in DispatchCall(),
// which will make it correct again
}
#ifdef OS_WIN
SyncStackFrame frame(this, true);
#endif
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DispatchIncall(call);
}
void
RPCChannel::DispatchIncall(const Message& call)
{
AssertWorkerThread();
mMonitor->AssertNotCurrentThreadOwns();
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RPC_ASSERT(call.is_rpc() && !call.is_reply(),
"wrong message type");
Message* reply = nullptr;
++mRemoteStackDepthGuess;
Result rv = Listener()->OnCallReceived(call, reply);
--mRemoteStackDepthGuess;
if (!MaybeHandleError(rv, "RPCChannel")) {
delete reply;
reply = new Message();
reply->set_rpc();
reply->set_reply();
reply->set_reply_error();
}
reply->set_seqno(call.seqno());
{
MonitorAutoLock lock(*mMonitor);
if (ChannelConnected == mChannelState)
mLink->SendMessage(reply);
}
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}
bool
RPCChannel::BlockChild()
{
AssertWorkerThread();
if (mChild)
NS_RUNTIMEABORT("child tried to block parent");
MonitorAutoLock lock(*mMonitor);
SendSpecialMessage(new BlockChildMessage());
return true;
}
bool
RPCChannel::UnblockChild()
{
AssertWorkerThread();
if (mChild)
NS_RUNTIMEABORT("child tried to unblock parent");
MonitorAutoLock lock(*mMonitor);
SendSpecialMessage(new UnblockChildMessage());
return true;
}
bool
RPCChannel::OnSpecialMessage(uint16_t id, const Message& msg)
{
AssertWorkerThread();
switch (id) {
case BLOCK_CHILD_MESSAGE_TYPE:
BlockOnParent();
return true;
case UNBLOCK_CHILD_MESSAGE_TYPE:
UnblockFromParent();
return true;
default:
return SyncChannel::OnSpecialMessage(id, msg);
}
}
void
RPCChannel::BlockOnParent()
{
AssertWorkerThread();
if (!mChild)
NS_RUNTIMEABORT("child tried to block parent");
MonitorAutoLock lock(*mMonitor);
if (mBlockedOnParent || AwaitingSyncReply() || 0 < StackDepth())
NS_RUNTIMEABORT("attempt to block child when it's already blocked");
mBlockedOnParent = true;
do {
// XXX this dispatch loop shares some similarities with the
// one in Call(), but the logic is simpler and different
// enough IMHO to warrant its own dispatch loop
while (Connected() && mPending.empty() && mBlockedOnParent) {
WaitForNotify();
}
if (!Connected()) {
mBlockedOnParent = false;
ReportConnectionError("RPCChannel");
break;
}
if (!mPending.empty()) {
Message recvd = mPending.front();
mPending.pop_front();
MonitorAutoUnlock unlock(*mMonitor);
CxxStackFrame f(*this, IN_MESSAGE, &recvd);
if (recvd.is_rpc()) {
// stack depth must be 0 here
Incall(recvd, 0);
}
else if (recvd.is_sync()) {
SyncChannel::OnDispatchMessage(recvd);
}
else {
AsyncChannel::OnDispatchMessage(recvd);
}
}
} while (mBlockedOnParent);
EnqueuePendingMessages();
}
void
RPCChannel::UnblockFromParent()
{
AssertWorkerThread();
if (!mChild)
NS_RUNTIMEABORT("child tried to block parent");
MonitorAutoLock lock(*mMonitor);
mBlockedOnParent = false;
}
void
RPCChannel::ExitedCxxStack()
{
Listener()->OnExitedCxxStack();
if (mSawRPCOutMsg) {
MonitorAutoLock lock(*mMonitor);
// see long comment in OnMaybeDequeueOne()
EnqueuePendingMessages();
mSawRPCOutMsg = false;
}
}
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void
RPCChannel::DebugAbort(const char* file, int line, const char* cond,
const char* why,
const char* type, bool reply) const
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{
printf_stderr("###!!! [RPCChannel][%s][%s:%d] "
"Assertion (%s) failed. %s (triggered by %s%s)\n",
mChild ? "Child" : "Parent",
file, line, cond,
why,
type, reply ? "reply" : "");
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// technically we need the mutex for this, but we're dying anyway
DumpRPCStack(" ");
printf_stderr(" remote RPC stack guess: %lu\n",
mRemoteStackDepthGuess);
printf_stderr(" deferred stack size: %lu\n",
mDeferred.size());
printf_stderr(" out-of-turn RPC replies stack size: %lu\n",
mOutOfTurnReplies.size());
printf_stderr(" Pending queue size: %lu, front to back:\n",
mPending.size());
MessageQueue pending = mPending;
while (!pending.empty()) {
printf_stderr(" [ %s%s ]\n",
pending.front().is_rpc() ? "rpc" :
(pending.front().is_sync() ? "sync" : "async"),
pending.front().is_reply() ? "reply" : "");
pending.pop_front();
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}
NS_RUNTIMEABORT(why);
}
void
RPCChannel::DumpRPCStack(const char* const pfx) const
{
NS_WARN_IF_FALSE(MessageLoop::current() != mWorkerLoop,
"The worker thread had better be paused in a debugger!");
printf_stderr("%sRPCChannel 'backtrace':\n", pfx);
// print a python-style backtrace, first frame to last
for (uint32_t i = 0; i < mCxxStackFrames.size(); ++i) {
int32_t id;
const char* dir, *sems, *name;
mCxxStackFrames[i].Describe(&id, &dir, &sems, &name);
printf_stderr("%s[(%u) %s %s %s(actor=%d) ]\n", pfx,
i, dir, sems, name, id);
}
}
//
// The methods below run in the context of the link thread, and can proxy
// back to the methods above
//
void
RPCChannel::OnMessageReceivedFromLink(const Message& msg)
{
AssertLinkThread();
mMonitor->AssertCurrentThreadOwns();
if (MaybeInterceptSpecialIOMessage(msg))
return;
// regardless of the RPC stack, if we're awaiting a sync reply, we
// know that it needs to be immediately handled to unblock us.
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if (AwaitingSyncReply() && msg.is_sync()) {
// wake up worker thread waiting at SyncChannel::Send
mRecvd = msg;
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NotifyWorkerThread();
return;
}
bool compressMessage = (msg.compress() && !mPending.empty() &&
mPending.back().type() == msg.type() &&
mPending.back().routing_id() == msg.routing_id());
if (compressMessage) {
// This message type has compression enabled, and the back of
// the queue was the same message type and routed to the same
// destination. Replace it with the newer message.
MOZ_ASSERT(mPending.back().compress());
mPending.pop_back();
}
mPending.push_back(msg);
if (0 == StackDepth() && !mBlockedOnParent) {
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// the worker thread might be idle, make sure it wakes up
if (!compressMessage) {
// If we compressed away the previous message, we'll reuse
// its pending task.
mWorkerLoop->PostTask(FROM_HERE, new DequeueTask(mDequeueOneTask));
}
}
else if (!AwaitingSyncReply())
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NotifyWorkerThread();
}
void
RPCChannel::OnChannelErrorFromLink()
{
AssertLinkThread();
mMonitor->AssertCurrentThreadOwns();
if (0 < StackDepth())
NotifyWorkerThread();
SyncChannel::OnChannelErrorFromLink();
}
} // namespace ipc
} // namespace mozilla
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