Tuesday, 11 June 2013

Synchronization Tools



Atomic operations – Atomic operations are a simple form of synchronization that work on simple data types. The advantage of atomic operations is that they do not block competing threads. For simple operations such as incrementing a counter variable, this can lead to much better performance than taking a lock.
Memory Barriers a volatile variables – In order to achieve optimal performance, compilers often reorder assembly-level instructions to keep the instruction pipeline for the processor as full as possible. A memory barrier is a type of nonblocking synchronization tool used to ensure that memory operations occur in the correct order.
Locks – Locks are one of the most commonly used synchronized tools. You can use locks to protect a critical section of your code, which is a segment of code that only one thread at a time is allowed access. For eg. a critical section. If one thread is synchronized on an object, and a second thread tries to synchronize on the same object, the second thread is forced to wait until the first thread has finished with the object. This is implemented using lock. Every object has a lock, and that lock can be ‘held’ only by one thread at a time. To enter a synchronized statement a thread must obtain the associated object lock. if thread A tries to obtain a lock that is already held by thread B, then thread A has to wait until thread B release the lock. In fact, thread A will go to sleep, and will not be awoken until the lock becomes available.

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