diff options
| -rw-r--r-- | src/corelib/thread/qmutex_linux.cpp | 37 |
1 files changed, 35 insertions, 2 deletions
diff --git a/src/corelib/thread/qmutex_linux.cpp b/src/corelib/thread/qmutex_linux.cpp index b1618f7fc9..1bb5e77e77 100644 --- a/src/corelib/thread/qmutex_linux.cpp +++ b/src/corelib/thread/qmutex_linux.cpp @@ -45,15 +45,47 @@ #ifndef QT_NO_THREAD #include "qatomic.h" #include "qmutex_p.h" -# include "qelapsedtimer.h" +#include "qelapsedtimer.h" #include <linux/futex.h> #include <sys/syscall.h> #include <unistd.h> #include <errno.h> +#ifndef QT_LINUX_FUTEX +# error "Qt build is broken: qmutex_linux.cpp is being built but futex support is not wanted" +#endif + QT_BEGIN_NAMESPACE +static inline int futexFlags() +{ + int value = 0; +#if defined(FUTEX_PRIVATE_FLAG) + // check if the kernel supports extra futex flags + // FUTEX_PRIVATE_FLAG appeared in v2.6.22 + static QBasicAtomicInt futexFlagSupport = Q_BASIC_ATOMIC_INITIALIZER(-1); + + value = futexFlagSupport.load(); + if (value == -1) { + // try an operation that has no side-effects: wake up 42 threads + // futex will return -1 (errno==ENOSYS) if the flag isn't supported + // there should be no other error conditions + value = syscall(SYS_futex, &futexFlagSupport, + FUTEX_WAKE | FUTEX_PRIVATE_FLAG, + 42, 0, 0, 0); + if (value != -1) { + value = FUTEX_PRIVATE_FLAG; + futexFlagSupport.store(value); + return value; + } + value = 0; + futexFlagSupport.store(value); + } +#endif + return value; +} + static inline int _q_futex(void *addr, int op, int val, const struct timespec *timeout) { volatile int *int_addr = reinterpret_cast<volatile int *>(addr); @@ -62,7 +94,8 @@ static inline int _q_futex(void *addr, int op, int val, const struct timespec *t #endif int *addr2 = 0; int val2 = 0; - return syscall(SYS_futex, int_addr, op, val, timeout, addr2, val2); + + return syscall(SYS_futex, int_addr, op | futexFlags(), val, timeout, addr2, val2); } static inline QMutexData *dummyFutexValue() |