From 634f82f1f1fda7983abf70b58e43c580b1f01df0 Mon Sep 17 00:00:00 2001 From: Thiago Macieira Date: Mon, 6 Aug 2012 19:57:59 +0200 Subject: Add a testAndSet overload to the atomics that returns the current value This is extremely useful, since the most common action after a failed compare-and-swap is to loop around, trying again with the current value as found in memory. Code currently written as: do { Type value = atomic.load(); ... } while (!atomic.testAndSetRelaxed(value, desired)); Becomes: Type value = atomic.load(); do { ... } while (!atomic.testAndSetRelaxed(value, desired, value)); In most CPU architectures, the value that was found in memory is known to the compare-and-swap code, so this is more efficient than the previous code. In architectures where the value is not known, the new code is no worse than before. The implementation sometimes modified an existing function, sometimes it added a new one, depending on whether more registers were needed in the assembly (like ARMv6-7), the code became more complex (ARMv5), the optimizer failed (C++11), or it was just plain equivalent (MIPS). Change-Id: I7d6d200ea9746ec8978a0c1e1969dbc3580b9285 Reviewed-by: Oswald Buddenhagen Reviewed-by: Lars Knoll Reviewed-by: Thiago Macieira --- src/corelib/arch/qatomic_ia64.h | 40 ++++++++++++++++++++++++++++------------ 1 file changed, 28 insertions(+), 12 deletions(-) (limited to 'src/corelib/arch/qatomic_ia64.h') diff --git a/src/corelib/arch/qatomic_ia64.h b/src/corelib/arch/qatomic_ia64.h index 0075f32a42..e5e93ec2b7 100644 --- a/src/corelib/arch/qatomic_ia64.h +++ b/src/corelib/arch/qatomic_ia64.h @@ -150,10 +150,10 @@ template struct QBasicAtomicOps: QGenericAtomicOps static bool testAndSetRelaxed(T &_q_value, T expectedValue, T newValue) Q_DECL_NOTHROW; - template static bool testAndSetAcquire(T &_q_value, T expectedValue, T newValue) Q_DECL_NOTHROW; - template static bool testAndSetRelease(T &_q_value, T expectedValue, T newValue) Q_DECL_NOTHROW; - template static bool testAndSetOrdered(T &_q_value, T expectedValue, T newValue) Q_DECL_NOTHROW; + template static bool testAndSetRelaxed(T &_q_value, T expectedValue, T newValue, T *currentValue = 0) Q_DECL_NOTHROW; + template static bool testAndSetAcquire(T &_q_value, T expectedValue, T newValue, T *currentValue = 0) Q_DECL_NOTHROW; + template static bool testAndSetRelease(T &_q_value, T expectedValue, T newValue, T *currentValue = 0) Q_DECL_NOTHROW; + template static bool testAndSetOrdered(T &_q_value, T expectedValue, T newValue, T *currentValue = 0) Q_DECL_NOTHROW; static inline Q_DECL_CONSTEXPR bool isFetchAndStoreNative() Q_DECL_NOTHROW { return true; } static inline Q_DECL_CONSTEXPR bool isFetchAndStoreWaitFree() Q_DECL_NOTHROW { return true; } @@ -373,7 +373,7 @@ bool QBasicAtomicOps<8>::deref(T &_q_value) Q_DECL_NOTHROW } template<> template inline -bool QBasicAtomicOps<1>::testAndSetAcquire(T &_q_value, T expectedValue, T newValue) Q_DECL_NOTHROW +bool QBasicAtomicOps<1>::testAndSetAcquire(T &_q_value, T expectedValue, T newValue, T *currentValue) Q_DECL_NOTHROW { T ret; asm volatile("mov ar.ccv=%2\n" @@ -382,11 +382,13 @@ bool QBasicAtomicOps<1>::testAndSetAcquire(T &_q_value, T expectedValue, T newVa : "=r" (ret), "+m" (_q_value) : "r" (expectedValue), "r" (newValue) : "memory"); + if (currentValue) + *currentValue = ret; return ret == expectedValue; } template<> template inline -bool QBasicAtomicOps<1>::testAndSetRelease(T &_q_value, T expectedValue, T newValue) Q_DECL_NOTHROW +bool QBasicAtomicOps<1>::testAndSetRelease(T &_q_value, T expectedValue, T newValue, T *currentValue) Q_DECL_NOTHROW { T ret; asm volatile("mov ar.ccv=%2\n" @@ -395,11 +397,13 @@ bool QBasicAtomicOps<1>::testAndSetRelease(T &_q_value, T expectedValue, T newVa : "=r" (ret), "+m" (_q_value) : "r" (expectedValue), "r" (newValue) : "memory"); + if (currentValue) + *currentValue = ret; return ret == expectedValue; } template<> template inline -bool QBasicAtomicOps<2>::testAndSetAcquire(T &_q_value, T expectedValue, T newValue) Q_DECL_NOTHROW +bool QBasicAtomicOps<2>::testAndSetAcquire(T &_q_value, T expectedValue, T newValue, T *currentValue) Q_DECL_NOTHROW { T ret; asm volatile("mov ar.ccv=%2\n" @@ -408,11 +412,13 @@ bool QBasicAtomicOps<2>::testAndSetAcquire(T &_q_value, T expectedValue, T newVa : "=r" (ret), "+m" (_q_value) : "r" (expectedValue), "r" (newValue) : "memory"); + if (currentValue) + *currentValue = ret; return ret == expectedValue; } template<> template inline -bool QBasicAtomicOps<2>::testAndSetRelease(T &_q_value, T expectedValue, T newValue) Q_DECL_NOTHROW +bool QBasicAtomicOps<2>::testAndSetRelease(T &_q_value, T expectedValue, T newValue, T *currentValue) Q_DECL_NOTHROW { T ret; asm volatile("mov ar.ccv=%2\n" @@ -421,11 +427,13 @@ bool QBasicAtomicOps<2>::testAndSetRelease(T &_q_value, T expectedValue, T newVa : "=r" (ret), "+m" (_q_value) : "r" (expectedValue), "r" (newValue) : "memory"); + if (currentValue) + *currentValue = ret; return ret == expectedValue; } template<> template inline -bool QBasicAtomicOps<4>::testAndSetAcquire(T &_q_value, T expectedValue, T newValue) Q_DECL_NOTHROW +bool QBasicAtomicOps<4>::testAndSetAcquire(T &_q_value, T expectedValue, T newValue, T *currentValue) Q_DECL_NOTHROW { T ret; asm volatile("mov ar.ccv=%2\n" @@ -434,11 +442,13 @@ bool QBasicAtomicOps<4>::testAndSetAcquire(T &_q_value, T expectedValue, T newVa : "=r" (ret), "+m" (_q_value) : "r" (expectedValue), "r" (newValue) : "memory"); + if (currentValue) + *currentValue = ret; return ret == expectedValue; } template<> template inline -bool QBasicAtomicOps<4>::testAndSetRelease(T &_q_value, T expectedValue, T newValue) Q_DECL_NOTHROW +bool QBasicAtomicOps<4>::testAndSetRelease(T &_q_value, T expectedValue, T newValue, T *currentValue) Q_DECL_NOTHROW { T ret; asm volatile("mov ar.ccv=%2\n" @@ -447,11 +457,13 @@ bool QBasicAtomicOps<4>::testAndSetRelease(T &_q_value, T expectedValue, T newVa : "=r" (ret), "+m" (_q_value) : "r" (expectedValue), "r" (newValue) : "memory"); + if (currentValue) + *currentValue = ret; return ret == expectedValue; } template<> template inline -bool QBasicAtomicOps<8>::testAndSetAcquire(T &_q_value, T expectedValue, T newValue) Q_DECL_NOTHROW +bool QBasicAtomicOps<8>::testAndSetAcquire(T &_q_value, T expectedValue, T newValue, T *currentValue) Q_DECL_NOTHROW { T ret; asm volatile("mov ar.ccv=%2\n" @@ -460,11 +472,13 @@ bool QBasicAtomicOps<8>::testAndSetAcquire(T &_q_value, T expectedValue, T newVa : "=r" (ret), "+m" (_q_value) : "r" (expectedValue), "r" (newValue) : "memory"); + if (currentValue) + *currentValue = ret; return ret == expectedValue; } template<> template inline -bool QBasicAtomicOps<8>::testAndSetRelease(T &_q_value, T expectedValue, T newValue) Q_DECL_NOTHROW +bool QBasicAtomicOps<8>::testAndSetRelease(T &_q_value, T expectedValue, T newValue, T *currentValue) Q_DECL_NOTHROW { T ret; asm volatile("mov ar.ccv=%2\n" @@ -473,6 +487,8 @@ bool QBasicAtomicOps<8>::testAndSetRelease(T &_q_value, T expectedValue, T newVa : "=r" (ret), "+m" (_q_value) : "r" (expectedValue), "r" (newValue) : "memory"); + if (currentValue) + *currentValue = ret; return ret == expectedValue; } -- cgit v1.2.3