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libcamera: signal: Make connection and disconnection thread-safe

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Make the signal connection and disconnection thread-safe, and document
them as such. This is required to make objects connectable from
different threads.

The connect(), disconnect() and emit() methods are now all protected by
a global mutex, which may generate a high lock contention. This could be
improved with finer-grained locks or with a pool of mutexes.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>
Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>
This commit is contained in:
Laurent Pinchart
2020-01-19 04:59:02 +02:00
parent 89503199e8
commit 09c45cc1fa
1 changed files with 33 additions and 0 deletions
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33
src/libcamera/signal.cpp
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@@ -7,6 +7,8 @@
#include <libcamera/signal.h>
#include "thread.h"
/**
* \file signal.h
* \brief Signal & slot implementation
@@ -14,8 +16,21 @@
namespace libcamera {
namespace {
/*
* Mutex to protect the SignalBase::slots_ and Object::signals_ lists. If lock
* contention needs to be decreased, this could be replaced with locks in
* Object and SignalBase, or with a mutex pool.
*/
Mutex signalsLock;
} /* namespace */
void SignalBase::connect(BoundMethodBase *slot)
{
MutexLocker locker(signalsLock);
Object *object = slot->object();
if (object)
object->connect(this);
@@ -31,6 +46,8 @@ void SignalBase::disconnect(Object *object)
void SignalBase::disconnect(std::function<bool(SlotList::iterator &)> match)
{
MutexLocker locker(signalsLock);
for (auto iter = slots_.begin(); iter != slots_.end(); ) {
if (match(iter)) {
Object *object = (*iter)->object();
@@ -47,6 +64,7 @@ void SignalBase::disconnect(std::function<bool(SlotList::iterator &)> match)
SignalBase::SlotList SignalBase::slots()
{
MutexLocker locker(signalsLock);
return slots_;
}
@@ -99,23 +117,31 @@ SignalBase::SlotList SignalBase::slots()
* disconnected from the \a func slot of \a object when \a object is destroyed.
* Otherwise the caller shall disconnect signals manually before destroying \a
* object.
*
* \context This function is \threadsafe.
*/
/**
* \fn Signal::connect(R (*func)(Args...))
* \brief Connect the signal to a static function slot
* \param[in] func The slot static function
*
* \context This function is \threadsafe.
*/
/**
* \fn Signal::disconnect()
* \brief Disconnect the signal from all slots
*
* \context This function is \threadsafe.
*/
/**
* \fn Signal::disconnect(T *object)
* \brief Disconnect the signal from all slots of the \a object
* \param[in] object The object pointer whose slots to disconnect
*
* \context This function is \threadsafe.
*/
/**
@@ -123,12 +149,16 @@ SignalBase::SlotList SignalBase::slots()
* \brief Disconnect the signal from the \a object slot member function \a func
* \param[in] object The object pointer whose slots to disconnect
* \param[in] func The slot member function to disconnect
*
* \context This function is \threadsafe.
*/
/**
* \fn Signal::disconnect(R (*func)(Args...))
* \brief Disconnect the signal from the slot static function \a func
* \param[in] func The slot static function to disconnect
*
* \context This function is \threadsafe.
*/
/**
@@ -141,6 +171,9 @@ SignalBase::SlotList SignalBase::slots()
* function are passed to the slot functions unchanged. If a slot modifies one
* of the arguments (when passed by pointer or reference), the modification is
* thus visible to all subsequently called slots.
*
* This function is not \threadsafe, but thread-safety is guaranteed against
* concurrent connect() and disconnect() calls.
*/
} /* namespace libcamera */