
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: Paolo Bonzini <pbonzini@redhat.com> Reviewed-by: Fam Zheng <famz@redhat.com> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com> Message-id: 20170112180800.21085-3-pbonzini@redhat.com Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
212 lines
5.9 KiB
C
212 lines
5.9 KiB
C
#ifndef QEMU_THREAD_H
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#define QEMU_THREAD_H
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#include "qemu/processor.h"
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#include "qemu/atomic.h"
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typedef struct QemuMutex QemuMutex;
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typedef struct QemuCond QemuCond;
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typedef struct QemuSemaphore QemuSemaphore;
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typedef struct QemuEvent QemuEvent;
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typedef struct QemuLockCnt QemuLockCnt;
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typedef struct QemuThread QemuThread;
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#ifdef _WIN32
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#include "qemu/thread-win32.h"
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#else
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#include "qemu/thread-posix.h"
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#endif
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#define QEMU_THREAD_JOINABLE 0
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#define QEMU_THREAD_DETACHED 1
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void qemu_mutex_init(QemuMutex *mutex);
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void qemu_mutex_destroy(QemuMutex *mutex);
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void qemu_mutex_lock(QemuMutex *mutex);
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int qemu_mutex_trylock(QemuMutex *mutex);
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void qemu_mutex_unlock(QemuMutex *mutex);
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/* Prototypes for other functions are in thread-posix.h/thread-win32.h. */
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void qemu_rec_mutex_init(QemuRecMutex *mutex);
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void qemu_cond_init(QemuCond *cond);
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void qemu_cond_destroy(QemuCond *cond);
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/*
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* IMPORTANT: The implementation does not guarantee that pthread_cond_signal
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* and pthread_cond_broadcast can be called except while the same mutex is
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* held as in the corresponding pthread_cond_wait calls!
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*/
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void qemu_cond_signal(QemuCond *cond);
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void qemu_cond_broadcast(QemuCond *cond);
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void qemu_cond_wait(QemuCond *cond, QemuMutex *mutex);
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void qemu_sem_init(QemuSemaphore *sem, int init);
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void qemu_sem_post(QemuSemaphore *sem);
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void qemu_sem_wait(QemuSemaphore *sem);
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int qemu_sem_timedwait(QemuSemaphore *sem, int ms);
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void qemu_sem_destroy(QemuSemaphore *sem);
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void qemu_event_init(QemuEvent *ev, bool init);
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void qemu_event_set(QemuEvent *ev);
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void qemu_event_reset(QemuEvent *ev);
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void qemu_event_wait(QemuEvent *ev);
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void qemu_event_destroy(QemuEvent *ev);
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void qemu_thread_create(QemuThread *thread, const char *name,
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void *(*start_routine)(void *),
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void *arg, int mode);
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void *qemu_thread_join(QemuThread *thread);
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void qemu_thread_get_self(QemuThread *thread);
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bool qemu_thread_is_self(QemuThread *thread);
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void qemu_thread_exit(void *retval);
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void qemu_thread_naming(bool enable);
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struct Notifier;
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void qemu_thread_atexit_add(struct Notifier *notifier);
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void qemu_thread_atexit_remove(struct Notifier *notifier);
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typedef struct QemuSpin {
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int value;
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} QemuSpin;
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static inline void qemu_spin_init(QemuSpin *spin)
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{
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__sync_lock_release(&spin->value);
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}
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static inline void qemu_spin_lock(QemuSpin *spin)
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{
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while (unlikely(__sync_lock_test_and_set(&spin->value, true))) {
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while (atomic_read(&spin->value)) {
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cpu_relax();
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}
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}
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}
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static inline bool qemu_spin_trylock(QemuSpin *spin)
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{
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return __sync_lock_test_and_set(&spin->value, true);
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}
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static inline bool qemu_spin_locked(QemuSpin *spin)
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{
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return atomic_read(&spin->value);
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}
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static inline void qemu_spin_unlock(QemuSpin *spin)
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{
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__sync_lock_release(&spin->value);
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}
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struct QemuLockCnt {
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QemuMutex mutex;
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unsigned count;
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};
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/**
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* qemu_lockcnt_init: initialize a QemuLockcnt
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* @lockcnt: the lockcnt to initialize
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*
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* Initialize lockcnt's counter to zero and prepare its mutex
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* for usage.
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*/
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void qemu_lockcnt_init(QemuLockCnt *lockcnt);
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/**
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* qemu_lockcnt_destroy: destroy a QemuLockcnt
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* @lockcnt: the lockcnt to destruct
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*
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* Destroy lockcnt's mutex.
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*/
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void qemu_lockcnt_destroy(QemuLockCnt *lockcnt);
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/**
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* qemu_lockcnt_inc: increment a QemuLockCnt's counter
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* @lockcnt: the lockcnt to operate on
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*
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* If the lockcnt's count is zero, wait for critical sections
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* to finish and increment lockcnt's count to 1. If the count
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* is not zero, just increment it.
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*
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* Because this function can wait on the mutex, it must not be
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* called while the lockcnt's mutex is held by the current thread.
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* For the same reason, qemu_lockcnt_inc can also contribute to
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* AB-BA deadlocks. This is a sample deadlock scenario:
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*
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* thread 1 thread 2
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* -------------------------------------------------------
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* qemu_lockcnt_lock(&lc1);
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* qemu_lockcnt_lock(&lc2);
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* qemu_lockcnt_inc(&lc2);
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* qemu_lockcnt_inc(&lc1);
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*/
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void qemu_lockcnt_inc(QemuLockCnt *lockcnt);
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/**
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* qemu_lockcnt_dec: decrement a QemuLockCnt's counter
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* @lockcnt: the lockcnt to operate on
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*/
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void qemu_lockcnt_dec(QemuLockCnt *lockcnt);
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/**
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* qemu_lockcnt_dec_and_lock: decrement a QemuLockCnt's counter and
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* possibly lock it.
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* @lockcnt: the lockcnt to operate on
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*
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* Decrement lockcnt's count. If the new count is zero, lock
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* the mutex and return true. Otherwise, return false.
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*/
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bool qemu_lockcnt_dec_and_lock(QemuLockCnt *lockcnt);
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/**
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* qemu_lockcnt_dec_if_lock: possibly decrement a QemuLockCnt's counter and
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* lock it.
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* @lockcnt: the lockcnt to operate on
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*
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* If the count is 1, decrement the count to zero, lock
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* the mutex and return true. Otherwise, return false.
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*/
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bool qemu_lockcnt_dec_if_lock(QemuLockCnt *lockcnt);
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/**
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* qemu_lockcnt_lock: lock a QemuLockCnt's mutex.
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* @lockcnt: the lockcnt to operate on
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*
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* Remember that concurrent visits are not blocked unless the count is
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* also zero. You can use qemu_lockcnt_count to check for this inside a
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* critical section.
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*/
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void qemu_lockcnt_lock(QemuLockCnt *lockcnt);
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/**
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* qemu_lockcnt_unlock: release a QemuLockCnt's mutex.
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* @lockcnt: the lockcnt to operate on.
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*/
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void qemu_lockcnt_unlock(QemuLockCnt *lockcnt);
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/**
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* qemu_lockcnt_inc_and_unlock: combined unlock/increment on a QemuLockCnt.
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* @lockcnt: the lockcnt to operate on.
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*
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* This is the same as
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*
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* qemu_lockcnt_unlock(lockcnt);
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* qemu_lockcnt_inc(lockcnt);
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*
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* but more efficient.
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*/
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void qemu_lockcnt_inc_and_unlock(QemuLockCnt *lockcnt);
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/**
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* qemu_lockcnt_count: query a LockCnt's count.
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* @lockcnt: the lockcnt to query.
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*
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* Note that the count can change at any time. Still, while the
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* lockcnt is locked, one can usefully check whether the count
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* is non-zero.
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*/
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unsigned qemu_lockcnt_count(QemuLockCnt *lockcnt);
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#endif
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