Hi,
Recent versions of live555 use std::atomic_flag array to work with
event triggers. Consider the following code fragment:
#ifndef NO_STD_LIB
if (fTriggersAwaitingHandling[i].test()) {
fTriggersAwaitingHandling[i].clear();
#else
It is problematic in two ways: 1) it's not atomic: the value can be
changed elsewhere between test() and clear() and 2) it requires
C++>=20. This can be easily fixed by replacing std::atomic_flag with
std::atomic_bool, that needs just C++11. The patch is attached, maybe
you find it useful.
- Dmitry Bely
--- a/BasicUsageEnvironment/BasicTaskScheduler.cpp
+++ b/BasicUsageEnvironment/BasicTaskScheduler.cpp
@@ -188,8 +188,8 @@
if (mask == 0) mask = EVENT_TRIGGER_ID_HIGH_BIT;
#ifndef NO_STD_LIB
- if (fTriggersAwaitingHandling[i].test()) {
- fTriggersAwaitingHandling[i].clear();
+ bool state = true;
+ if (fTriggersAwaitingHandling[i].compare_exchange_strong(state, false)) {
#else
if (fTriggersAwaitingHandling[i]) {
fTriggersAwaitingHandling[i] = False;
--- a/BasicUsageEnvironment/BasicTaskScheduler0.cpp
+++ b/BasicUsageEnvironment/BasicTaskScheduler0.cpp
@@ -50,7 +50,7 @@
fHandlers = new HandlerSet;
for (unsigned i = 0; i < MAX_NUM_EVENT_TRIGGERS; ++i) {
#ifndef NO_STD_LIB
- fTriggersAwaitingHandling[i].clear();
+ fTriggersAwaitingHandling[i].store(false);
#else
fTriggersAwaitingHandling[i] = False;
#endif
@@ -123,7 +123,7 @@
for (unsigned i = 0; i < MAX_NUM_EVENT_TRIGGERS; ++i) {
if ((eventTriggerId&mask) != 0) {
#ifndef NO_STD_LIB
- fTriggersAwaitingHandling[i].clear();
+ fTriggersAwaitingHandling[i].store(false);
#else
fTriggersAwaitingHandling[i] = False;
#endif
@@ -145,7 +145,7 @@
if ((eventTriggerId&mask) != 0) {
fTriggeredEventClientDatas[i] = clientData;
#ifndef NO_STD_LIB
- (void)fTriggersAwaitingHandling[i].test_and_set();
+ fTriggersAwaitingHandling[i].store(true);
#else
fTriggersAwaitingHandling[i] = True;
#endif
--- a/BasicUsageEnvironment/include/BasicUsageEnvironment0.hh
+++ b/BasicUsageEnvironment/include/BasicUsageEnvironment0.hh
@@ -117,7 +117,7 @@
// To implement event triggers:
#ifndef NO_STD_LIB
- std::atomic_flag fTriggersAwaitingHandling[MAX_NUM_EVENT_TRIGGERS];
+ std::atomic_bool fTriggersAwaitingHandling[MAX_NUM_EVENT_TRIGGERS];
#else
Boolean volatile fTriggersAwaitingHandling[MAX_NUM_EVENT_TRIGGERS];
#endif
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