Using Thread Locks to Protect Data

Use a thread lock in applications with multiple threads to prevent multiple threads from performing a specific action at the same time. The thread lock is a wrapper around a simple OS thread-locking object and serializes access to segments of code from more than one thread or process. This prevents more than one thread from having access to data or a segment of code at the same time.

There are three circumstances under which you might use a thread lock.

• If you have a section of code that accesses many shared data variables, you might want to acquire a thread lock before executing the code and release the thread lock after executing the code. The benefit of this approach is that the code is simpler and less error prone than an approach where you protect each piece of data individually. The drawback is decreased performance because threads in your program will tend to hold the lock longer than is actually necessary, which causes other threads to block (wait) longer than necessary to obtain a lock.
• Another circumstance under which you might want to use a lock is to protect access to third-party libraries or code that is not thread safe. If, for example, you have a non-thread safe DLL that controls a piece of hardware and you want to call the DLL from more than one thread, you can create a lock that your threads must acquire before calling into the DLL.
• The third circumstance under which you might use a thread lock is to protect resources that are shared between programs. Shared memory is an example of such a resource.