Download source files - 2 Kb
This article describes a set of classes that are used to perform synchronization
between different threads. The class diagram below should explain the idea:
At the root, there is a
TSynchroBase class that has 2 abstract virtual methods:
DoLock() and (2)
DoUnlock(). These 2 methods are implemented in derived
classes because they contain selected synchronization method specific code.
Two concrete classes are supplied:
TSynchroMutex that uses a mutex for synchronization.
TSynchroCriticalSection that uses a critical section for synchronization.
However, additional classes may be implemented (for example, a class that uses
events or semaphores).
When synchronization is used in the application, one has to take care that
the synchronization object is unlocked once the thread that took ownership of the
synchronization object is finished with it. If this is not done, other threads
will be blocked. This can be difficult and error prone in a complex function
where there is more then one exit point from a function. A simple solution is
to move the protected code to a function and this function is called after taking
ownership of the synchronization object. After the function, the synchronization
object is released. This is illustrated in the following sample code.
Error prone example:
In the first example it is easy to forget a single
Unlock() which is a logical
error that may block other threads since they cannot take ownership of the
The second example clutters the code with unnecessary functions.
TSynchroTransient class is designed to solve this problem. It takes a pointer
to a synchronization object in a constructor and immediately takes ownership
of the synchronization object. It will automatically release the synchronization
object in its destructor.
For this to function properly, it is necessary that the
is created on the stack -- it will be automatically destroyed when the function
IsLocked() check is needed only if you use a synchronization method that
may fail (for example, mutex). If you use critical sections, it is not necessary
to call this function since entering critical section blocks until is succeeds.