multithreading - TMREWSync(TMultiReadExclusiveWriteSynchronizer)问题

Question

我对TMREWSync有疑问:

是否可以在不解锁的情况下将“读取锁定”升级为“写入锁定”？

不明白如果BeginWrite返回false怎么办？

Answer 1

是，TMREWSync支持锁升级。像这样使用它:BeginRead ... BeginWrite ... EndWrite ... EndRead。

System.SysUtils状态中的源代码:

The function result of BeginWrite indicates whether another thread got the write lock while the current thread was waiting for the write lock. Return value of True means that the write lock was acquired without any intervening modifications by other threads. Return value of False means another thread got the write lock while you were waiting, so the resource protected by the MREWS object should be considered modified. Any samples of the protected resource should be discarded.

我的建议是编写算法，使其不依赖于此返回值。源代码与我一致:

In general, it's better to just always reacquire samples of the protected resource after obtaining a write lock. The boolean result of BeginWrite and the RevisionLevel property help cases where reacquiring the samples is computationally expensive or time consuming.