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The original form of the pattern, appearing in Pattern Languages of Program Design 3, [2] has data races, depending on the memory model in use, and it is hard to get right. Some consider it to be an anti-pattern. [3] There are valid forms of the pattern, including the use of the volatile keyword in Java and explicit memory barriers in C++. [4]
Most locking designs block the execution of the thread requesting the lock until it is allowed to access the locked resource. With a spinlock, the thread simply waits ("spins") until the lock becomes available. This is efficient if threads are blocked for a short time, because it avoids the overhead of operating system process re-scheduling.
The memory model specifies synchronization barriers that are established via special, well-defined synchronization operations such as acquiring a lock by entering a synchronized block or method. The memory model stipulates that changes to the values of shared variables only need to be made visible to other threads when such a synchronization ...
The Java memory model describes how threads in the Java programming language interact through memory. Together with the description of single-threaded execution of code, the memory model provides the semantics of the Java programming language.
The type of liveness requirements tend to define the data structure. The method calls can be blocking or non-blocking. Data structures are not restricted to one type or the other, and can allow combinations where some method calls are blocking and others are non-blocking (examples can be found in the Java concurrency software library).
Java synchronized blocks, in addition to enabling mutual exclusion and memory consistency, enable signaling—i.e. sending events from threads which have acquired the lock and are executing the code block to those which are waiting for the lock within the block. Java synchronized sections, therefore, combine the functionality of both mutexes ...
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When the other task is blocked, it is unable to execute until the first task has finished using the shared resource. Programming languages and scheduling algorithms are designed to minimize the over-all effect of blocking. A process that blocks may prevent local work-tasks from progressing. In this case "blocking" often is seen as not wanted. [2]