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authorLaurent Pinchart <laurent.pinchart@ideasonboard.com>2020-01-19 04:59:02 +0200
committerLaurent Pinchart <laurent.pinchart@ideasonboard.com>2020-02-13 12:34:34 +0200
commit09c45cc1faa9805124168de414df7eba007acfee (patch)
treecb34447950c27eccaef7b135ef5e8c7141bde303
parent89503199e8d09ac17e6d2dde7715a843ede77e5c (diff)
libcamera: signal: Make connection and disconnection thread-safe
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>
-rw-r--r--src/libcamera/signal.cpp33
1 files changed, 33 insertions, 0 deletions
diff --git a/src/libcamera/signal.cpp b/src/libcamera/signal.cpp
index 9bb7eca8..6eab1fa7 100644
--- a/src/libcamera/signal.cpp
+++ b/src/libcamera/signal.cpp
@@ -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 */