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Intel Threading Building Blocks by James Reinders

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Mutexes

A mutex is a global variable that multiple tasks can access. Before entering code that you do not want to execute concurrently, a task should request a lock on the mutex. If the mutex is already locked, the task is stalled waiting. Once the lock is granted, the task can proceed. The task should proceed quickly and release the lock on the mutex promptly to avoid unnecessary stalls in other tasks.

If a mutex creates a lot of lock requests, it is considered highly contested. Highly contested locks will result in many tasks being stalled and a sharp reduction in program scalability. Avoiding highly contested locks through careful program design is important.

A mutex, used properly, ensures that no task reads or writes a variable or other resource when another task is writing it. Intel Threading Building Blocks mutexes work with generic programming in C++, even in the presence of exceptions. Meeting all these requirements is no small feat and takes some consideration to ensure their proper usage.

In Threading Building Blocks, mutual exclusion is implemented by classes known as mutexes and locks. A mutex is an object on which a task can acquire a lock. Only one task at a time can have a lock on a mutex; other tasks have to wait their turn.

Mutual exclusion controls how many tasks can simultaneously run a region of code. In general, you protect a region of code from concurrency when that code reads or writes a small amount of memory, which is generally interrelated by a particular ...

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