<Threading and Parallel Programming Constructs ⁄ >

Synchronization is an enforcing mechanism used to impose constraints on the order of execution of threads. The synchronization controls the relative order of thread execution and resolves any conflict among threads that might produce unwanted behavior. In simple terms, synchronization is used to coordinate thread execution and manage shared data.

In an environment where messages are used for communicating between a sender and a receiver, synchronization is implicit, as a message must be sent before the message can be received. On the other hand, for a shared-memory based environment, threads have no implicit interdependency unless some constraints are imposed.

Two types of synchronization operations are widely used: mutual exclusion and condition synchronization. In the case of mutual exclusion, one thread blocks a critical section -- a section of code that contains shared data -- and one or more threads wait to get their turn to enter into the section. This helps when two or more threads share the same memory space and run simultaneously. The mutual exclusion is controlled by a scheduler and depends on the granularity of the scheduler. Condition synchronization, on the other hand, blocks a thread until the system state specifies some specific conditions. The condition synchronization allows a thread to wait until a specific condition is reached. Figure 1 shows the generic representation of synchronization.



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