noreply at mythtv
Jul 3, 2012, 4:23 AM
Post #2 of 16
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Re: Ticket #10870: Race condition between StreamHandler::RemoveListener and StreamHandler::AddListener
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#10870: Race condition between StreamHandler::RemoveListener and
StreamHandler::AddListener
----------------------------------------+----------------------------
Reporter: roger@… | Owner:
Type: Bug Report - Hang/Deadlock | Status: new
Priority: minor | Milestone: unknown
Component: MythTV - General | Version: 0.25-fixes
Severity: medium | Resolution:
Keywords: AddListener RemoveListener | Ticket locked: 0
----------------------------------------+----------------------------
Comment (by Roger James <roger@…>):
The patch below is solely intended as a work around, and I have put it
here for information only. I have regression tested it and done some very
basic testing against the issue I reported. It appears to work. I don't
like the idea of introducing extra locks to fix a bug, but it is the least
intrusive change I could think of. A better fix would possibly be the
implementation of a proper finite state machine with queued event
handling.
Roger
{{{
$ git diff streamhandler.cpp
diff --git a/mythtv/libs/libmythtv/streamhandler.cpp
b/mythtv/libs/libmythtv/str
index 2b0a7b6..28de368 100644
--- a/mythtv/libs/libmythtv/streamhandler.cpp
+++ b/mythtv/libs/libmythtv/streamhandler.cpp
@@ -133,7 +133,8 @@ void StreamHandler::RemoveListener(MPEGStreamData
*data)
void StreamHandler::Start(void)
{
- QMutexLocker locker(&_start_stop_lock);
+ QMutexLocker
start_stop_procedure_locker(&_start_stop_procedure_lock);
+ QMutexLocker start_stop_locker(&_start_stop_lock);
if (_running)
{
@@ -173,7 +174,8 @@ void StreamHandler::Start(void)
void StreamHandler::Stop(void)
{
- QMutexLocker locker(&_start_stop_lock);
+ QMutexLocker
start_stop_procedure_locker(&_start_stop_procedure_lock);
+ QMutexLocker start_stop_locker(&_start_stop_lock);
do
{
$ git diff streamhandler.h
diff --git a/mythtv/libs/libmythtv/streamhandler.h
b/mythtv/libs/libmythtv/strea
index 1db0584..ae0bc80 100644
--- a/mythtv/libs/libmythtv/streamhandler.h
+++ b/mythtv/libs/libmythtv/streamhandler.h
@@ -45,7 +45,7 @@ class PIDInfo
typedef QMap<uint,PIDInfo*> PIDInfoMap;
// locking order
-// _pid_lock -> _listener_lock -> _start_stop_lock
+// _pid_lock -> _listener_lock -> _start_stop_procedure_lock ->
_start_stop_lock
class StreamHandler : protected MThread, public DeviceReaderCB
{
@@ -93,7 +93,7 @@ class StreamHandler : protected MThread, public
DeviceReaderCB
virtual void RemoveNamedOutputFile(const QString &filename) {}
/// At minimum this sets _running_desired, this may also send
/// signals to anything that might be blocking the run() loop.
- /// \note: The _start_stop_lock must be held when this is called.
+ /// \note: The _start_stop_procedure_lock and the _start_stop_lock
must be
virtual void SetRunningDesired(bool desired) { _running_desired =
desired;
protected:
@@ -101,6 +101,7 @@ class StreamHandler : protected MThread, public
DeviceReader
bool _needs_buffering;
bool _allow_section_reader;
+ mutable QMutex _start_stop_procedure_lock; /// Serialises calls to
Start
mutable QMutex _start_stop_lock;
volatile bool _running_desired;
volatile bool _error;
$
}}}
--
Ticket URL: <http://code.mythtv.org/trac/ticket/10870#comment:1>
MythTV <http://code.mythtv.org/trac>
MythTV Media Center
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