QReadWriteLock 类提供读写锁定。 更多...
QReadWriteLock 类提供读写锁定。
A read-write lock is a synchronization tool for protecting resources that can be accessed for reading and writing. This type of lock is useful if you want to allow multiple threads to have simultaneous read-only access, but as soon as one thread wants to write to the resource, all other threads must be blocked until the writing is complete.
在很多情况下，QReadWriteLock 的直接竞争者是 QMutex . QReadWriteLock is a good choice if there are many concurrent reads and writing occurs infrequently.
范例：
QReadWriteLock lock; void ReaderThread.run() { ... lock.lockForRead(); read_file(); lock.unlock(); ... } void WriterThread.run() { ... lock.lockForWrite(); write_file(); lock.unlock(); ... }
To ensure that writers aren't blocked forever by readers, readers attempting to obtain a lock will not succeed if there is a blocked writer waiting for access, even if the lock is currently only accessed by other readers. Also, if the lock is accessed by a writer and another writer comes in, that writer will have priority over any readers that might also be waiting.
像 QMutex , a QReadWriteLock can be recursively locked by the same thread when constructed in QReadWriteLock.RecursionMode . In such cases, unlock () must be called the same number of times lockForWrite () 或 lockForRead () 被调用。 Note that the lock type cannot be changed when trying to lock recursively, i.e. it is not possible to lock for reading in a thread that already has locked for writing (and vice versa).
| 常量 | 值 | 描述 |
|---|---|---|
| QReadWriteLock.Recursive | 1 | In this mode, a thread can lock the same QReadWriteLock multiple times and the mutex won't be unlocked until a corresponding number of unlock () calls have been made. |
| QReadWriteLock.NonRecursive | 0 | In this mode, a thread may only lock a QReadWriteLock once. |
该枚举在 Qt 4.4 引入或被修改。
另请参阅 QReadWriteLock ().
构造 QReadWriteLock object in NonRecursive 模式。
另请参阅 lockForRead () 和 lockForWrite ().
构造 QReadWriteLock object in the given recursionMode .
该函数在 Qt 4.4 引入。
另请参阅 lockForRead (), lockForWrite ()，和 RecursionMode .
Locks the lock for reading. This function will block the current thread if any thread (including the current) has locked for writing.
另请参阅 unlock (), lockForWrite ()，和 tryLockForRead ().
Locks the lock for writing. This function will block the current thread if another thread has locked for reading or writing.
另请参阅 unlock (), lockForRead ()，和 tryLockForWrite ().
Attempts to lock for reading. If the lock was obtained, this function returns true, otherwise it returns false instead of waiting for the lock to become available, i.e. it does not 块。
The lock attempt will fail if another thread has locked for writing.
If the lock was obtained, the lock must be unlocked with unlock () before another thread can successfully lock it.
另请参阅 unlock () 和 lockForRead ().
这是重载函数。
Attempts to lock for reading. This function returns true if the lock was obtained; otherwise it returns false. If another thread has locked for writing, this function will wait for at most timeout milliseconds for the lock to become available.
Note: Passing a negative number as the timeout is equivalent to calling lockForRead (), i.e. this function will wait forever until lock can be locked for reading when timeout is negative.
If the lock was obtained, the lock must be unlocked with unlock () before another thread can successfully lock it.
另请参阅 unlock () 和 lockForRead ().
Attempts to lock for writing. If the lock was obtained, this function returns true; otherwise, it returns false immediately.
The lock attempt will fail if another thread has locked for reading or writing.
If the lock was obtained, the lock must be unlocked with unlock () before another thread can successfully lock it.
另请参阅 unlock () 和 lockForWrite ().
这是重载函数。
Attempts to lock for writing. This function returns true if the lock was obtained; otherwise it returns false. If another thread has locked for reading or writing, this function will wait for at most timeout milliseconds for the lock to become available.
Note: Passing a negative number as the timeout is equivalent to calling lockForWrite (), i.e. this function will wait forever until lock can be locked for writing when timeout is negative.
If the lock was obtained, the lock must be unlocked with unlock () before another thread can successfully lock it.
另请参阅 unlock () 和 lockForWrite ().
Unlocks the lock.
Attempting to unlock a lock that is not locked is an error, and will result in program termination.
另请参阅 lockForRead (), lockForWrite (), tryLockForRead ()，和 tryLockForWrite ().
