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The code using a java.util.concurrent.ReentrantReadWriteLock is similar to that for native synchronization. However, for safety, the locks should be used in a try/finally block so that early exit such as java.lang.Exception throwing or break/continue will be sure to pass through the
To synchronize threads, Java uses monitors, which are a high-level mechanism for allowing only one thread at a time to execute a region of code protected by the monitor. The behavior of monitors is explained in terms of locks ; there is a lock associated with each object.
The location (in memory) of the code for handling an exception need not be located within (or even near) the region of memory where the rest of the function's code is stored. So if an exception is thrown then a performance hit – roughly comparable to a function call [24] – may occur if the necessary exception handling code needs to be ...
Reentrant code may not modify itself without synchronization. The operating system might allow a process to modify its code. There are various reasons for this (e.g., blitting graphics quickly) but this generally requires synchronization to avoid problems with reentrancy. It may, however, modify itself if it resides in its own unique memory.
Lamport's bakery algorithm is a computer algorithm devised by computer scientist Leslie Lamport, as part of his long study of the formal correctness of concurrent systems, which is intended to improve the safety in the usage of shared resources among multiple threads by means of mutual exclusion.
In concurrent programming, concurrent accesses to shared resources can lead to unexpected or erroneous behavior. Thus, the parts of the program where the shared resource is accessed need to be protected in ways that avoid the concurrent access. One way to do so is known as a critical section or critical region. This protected section cannot be ...
(previous code) // About to enter the monitor. // Acquire the advisory mutex (lock) associated with the concurrent // data that is shared between threads, // to ensure that no two threads can be preemptively interleaved or // run simultaneously on different cores while executing in critical // sections that read or write this same concurrent data.
Some concurrency control strategies avoid some or all of these problems. For example, a funnel or serializing tokens can avoid the biggest problem: deadlocks. Alternatives to locking include non-blocking synchronization methods, like lock-free programming techniques and transactional memory. However, such alternative methods often require that ...