Readers-writer lock - Part 4: Improving TLightweightMREW

[DP News-Robot]

While the TLightweightMREW*is quite handy, it is not perfect. There's a weird assymmetry in it. On all operating systems that Delphi can compile for, read*locks are reentrant (recursive) while write*locks are not. In other words, if a thread already owns a read lock, it can call BeginRead*again and it will succeed. Write locks are different. If a thread already owns a write lock and calls BeginWrite*again, it will either deadlock (on Windows) or raise an exception (on other supported platforms).

This is, however, relatively simple to fix. I have implemented a simple wrapper for the TLightweightMREW lock in TLightweightMREWEx. This new record uses internal TLightweightMREW*to provide locking and adds some simple logic to implement write lock reentrancy. The implementation and accompanying test program rwReentrantWriter*can be found at*https://github.com/gabr42/examples/t...-writer%20lock.

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