Author: astitcher
Date: Wed Mar 11 18:40:54 2009
New Revision: 752560
URL: http://svn.apache.org/viewvc?rev=752560&view=rev
Log:
Remove race condition in low level IO when throttling input
to avoid overloading the clustering service
Modified:
qpid/trunk/qpid/cpp/src/qpid/sys/AsynchIOHandler.cpp
Modified: qpid/trunk/qpid/cpp/src/qpid/sys/AsynchIOHandler.cpp
URL:
http://svn.apache.org/viewvc/qpid/trunk/qpid/cpp/src/qpid/sys/AsynchIOHandler.cpp?rev=752560&r1=752559&r2=752560&view=diff
==============================================================================
--- qpid/trunk/qpid/cpp/src/qpid/sys/AsynchIOHandler.cpp (original)
+++ qpid/trunk/qpid/cpp/src/qpid/sys/AsynchIOHandler.cpp Wed Mar 11 18:40:54
2009
@@ -84,10 +84,11 @@
// Check whether we started in the don't about credit state
if (readCredit.boolCompareAndSwap(InfiniteCredit, credit))
return;
- else if (readCredit.fetchAndAdd(credit) != 0)
- return;
- // Lock and retest credit to make sure we don't race with decreasing credit
+ // TODO In theory should be able to use an atomic operation before taking
the lock
+ // but in practice there seems to be an unexplained race in that case
ScopedLock<Mutex> l(creditLock);
+ if (readCredit.fetchAndAdd(credit) != 0)
+ return;
assert(readCredit.get() >= 0);
if (readCredit.get() != 0)
aio->startReading();
@@ -141,9 +142,10 @@
}
// Check here for read credit
if (readCredit.get() != InfiniteCredit) {
+ // TODO In theory should be able to use an atomic operation before
taking the lock
+ // but in practice there seems to be an unexplained race in that case
+ ScopedLock<Mutex> l(creditLock);
if (--readCredit == 0) {
- // Lock and retest credit to make sure we don't race with
increasing credit
- ScopedLock<Mutex> l(creditLock);
assert(readCredit.get() >= 0);
if (readCredit.get() == 0) {
aio->stopReading();
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