path: root/tests/auto/corelib/kernel/qsharedmemory/sharedmemoryhelper/main.cpp
diff options
authorThiago Macieira <>2013-01-10 23:11:04 -0800
committerThe Qt Project <>2013-01-14 11:35:17 +0100
commit60fc88a09c0127bf79563e5449e049f3c9e0fc55 (patch)
treee7212863b58e794c3e8ffbc2cf1483d30cf37c6d /tests/auto/corelib/kernel/qsharedmemory/sharedmemoryhelper/main.cpp
parentaeb2941ca1dcb901ca8bd6b74af456c1473728a4 (diff)
Resolve some race conditions on tst_QSharedMemory
This test runs fine almost all of the time on systems with 1 processor, which were the norm when the test was written and are still the way that the Qt Continuous Integration system works as of today. But it falls flatly on multi-processor systems. The root of the problem is that QSystemSemaphore recreates the semaphore if it disappears underneath it. However, the recreation process is not thread-safe at all: if two threads race to recreate it, weird things might happen. strace on Linux shows that a thread got stuck trying to acquire the semaphore: <... nanosleep resumed> NULL) = 0 stat("/tmp/qipc_systemsem_market5c9f73af73334ffe350c60ec076e5744db0ecda3", {st_mode=S_IFREG|0640, st_size=0, ...}) = 0 stat("/tmp/qipc_systemsem_market5c9f73af73334ffe350c60ec076e5744db0ecda3", {st_mode=S_IFREG|0640, st_size=0, ...}) = 0 semget(0x51001388, 1, IPC_CREAT|IPC_EXCL|0600) = -1 EEXIST (File exists) semget(0x51001388, 1, IPC_CREAT|0600) = 114786308 semop(114786308, {{0, -1, SEM_UNDO}}, 1 <unfinished ...> This problem does not happen if the creation and destruction of the QSharedMemory (which uses QSystemSemaphore) does not race with other threads or processes attaching and detaching. For the threads test it's easy. For the processes, we use stdin and stdout as a communication channel. Change-Id: Ie11b135431d4abfc59234654848b67f622eb03c9 Reviewed-by: Richard J. Moore <>
Diffstat (limited to 'tests/auto/corelib/kernel/qsharedmemory/sharedmemoryhelper/main.cpp')
1 files changed, 6 insertions, 3 deletions
diff --git a/tests/auto/corelib/kernel/qsharedmemory/sharedmemoryhelper/main.cpp b/tests/auto/corelib/kernel/qsharedmemory/sharedmemoryhelper/main.cpp
index 63f38f43f3..30c9d01e98 100644
--- a/tests/auto/corelib/kernel/qsharedmemory/sharedmemoryhelper/main.cpp
+++ b/tests/auto/corelib/kernel/qsharedmemory/sharedmemoryhelper/main.cpp
@@ -43,6 +43,7 @@
#include <QStringList>
#include <QDebug>
#include <QTest>
+#include <stdio.h>
void set(QSharedMemory &sm, int pos, QChar value)
@@ -82,7 +83,10 @@ int producer()
+ // tell parent we're ready
//qDebug("producer created and attached");
+ puts("");
+ fflush(stdout);
if (!producer.lock()) {
qWarning() << "Could not lock" << producer.key();
@@ -129,9 +133,8 @@ int producer()
//qDebug("producer done");
- // Sleep for a bit to let all consumers start, otherwise they will get stuck in the attach loop,
- // because at least in Symbian the shared memory will be destroyed if there are no active handles to it.
- QTest::qSleep(3000);
+ // Sleep for a bit to let all consumers exit
+ getchar();