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QMutex: make FUTEX_PRIVATE_FLAG a mandatory feature

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The flag was introduced in kernel 2.6.22, but we're already depending on
features added on 2.6.23 in qcore_unix_p.h (pipe2, dup3, O_CLOEXEC) and
2.6.27 in qnet_unix_p.h (accept4 and SOCK_CLOEXEC).

Change-Id: Id5480807d25e49e78b79ffff144a093c9e30cd96
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
This commit is contained in:
Thiago Macieira 2016-04-29 21:39:44 -07:00
parent e2e0dfee7c
commit 9ef59b586d
1 changed files with 6 additions and 35 deletions
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41
src/corelib/thread/qmutex_linux.cpp
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@ -56,6 +56,11 @@
# error "Qt build is broken: qmutex_linux.cpp is being built but futex support is not wanted"
#endif
#ifndef FUTEX_PRIVATE_FLAG
# define FUTEX_PRIVATE_FLAG 128
#endif
QT_BEGIN_NAMESPACE
/*
@ -104,40 +109,6 @@ QT_BEGIN_NAMESPACE
static QBasicAtomicInt futexFlagSupport = Q_BASIC_ATOMIC_INITIALIZER(-1);
static int checkFutexPrivateSupport()
{
int value = 0;
#if defined(FUTEX_PRIVATE_FLAG)
// check if the kernel supports extra futex flags
// FUTEX_PRIVATE_FLAG appeared in v2.6.22
Q_STATIC_ASSERT(FUTEX_PRIVATE_FLAG != 0x80000000);
// 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(__NR_futex, &futexFlagSupport,
FUTEX_WAKE | FUTEX_PRIVATE_FLAG,
42, 0, 0, 0);
if (value != -1)
value = FUTEX_PRIVATE_FLAG;
else
value = 0;
#else
value = 0;
#endif
futexFlagSupport.store(value);
return value;
}
static inline int futexFlags()
{
int value = futexFlagSupport.load();
if (Q_LIKELY(value != -1))
return value;
return checkFutexPrivateSupport();
}
static inline int _q_futex(void *addr, int op, int val, const struct timespec *timeout) Q_DECL_NOTHROW
{
volatile int *int_addr = reinterpret_cast<volatile int *>(addr);
@ -149,7 +120,7 @@ static inline int _q_futex(void *addr, int op, int val, const struct timespec *t
// we use __NR_futex because some libcs (like Android's bionic) don't
// provide SYS_futex etc.
return syscall(__NR_futex, int_addr, op | futexFlags(), val, timeout, addr2, val2);
return syscall(__NR_futex, int_addr, op | FUTEX_PRIVATE_FLAG, val, timeout, addr2, val2);
}
static inline QMutexData *dummyFutexValue()