qemu-thread: introduce QemuLockCnt
A QemuLockCnt comprises a counter and a mutex, with primitives to increment and decrement the counter, and to take and release the mutex. It can be used to do lock-free visits to a data structure whenever mutexes would be too heavy-weight and the critical section is too long for RCU. This could be implemented simply by protecting the counter with the mutex, but QemuLockCnt is harder to misuse and more efficient. Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com> Reviewed-by: NFam Zheng <famz@redhat.com> Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com> Message-id: 20170112180800.21085-3-pbonzini@redhat.com Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>
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docs/lockcnt.txt
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util/lockcnt.c
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