The four synchronization models are mutex locks, read/write locks, condition variables, and semaphores. Synchronization allows you to control program flow and access to shared data for concurrently executing threads. synchronized and volatile keywords force that the changes are globally visible on a timely basis these help cross the memory barrier. “Memory Barrier” means copying data from local working memory to main memory.Ī change made by one thread is guaranteed to be visible to another thread only if the writing thread crosses the memory barrier and then the reading thread crosses the memory barrier. In order to make it visible, Memory Barrier is needed. Solution: synchronize or use atomic objects AtomicInteger.getAndSet() VisibilityĬhanges made by one thread may not be visible to other threads since the data could be residing in local working memory of a thread instead of main memory. ++ numRequests //non-atomic compound action Performs better than green threads even in single-coreĬompound Action Anti-Patterns Check-then-act.Can be scheduled across cores in multi-core or multiprocessor systems.

Uses cooperative multitasking - dangerous.

Sun wrote green threads to enable Java to work in environments that do not have native thread support.They run code in user space that manages and schedules threads Green threads emulate multithreaded environments without relying on any native OS capabilities.Can create problems if a thread is waiting for a resource to become available.The threads themselves determine relinquish control once they are at a stopping point.System may make context switch at an inappropriate time.OS determines when a context switch should occur.

Distributed processing - refers to two or more processes running asynchronously on one or more JVMs or boxes.

Concurrent processing - refers to two or more threads running asynchronously, on one or more cores, usually in the same computer.

Parallel processing - refers to two or more threads running simultaneously, on different cores (processors), in the same computer.

Threads share the memory address space of the owning process due to this, all threads have access to the same variables and allocate objects from same heap.

Each thread has its own stack and local variable.

Disadvantages of unbounded thread creation.

Java concurrency in practice pdf github