JavaScript has no locking semantics because JS is not a multi threaded language. Multiple threads can only operate concurrently in completely distinct contexts — eg. HTML5 Worker threads, or in things like multiple instances of JavaScriptCore API’s context object (I assume SpiderMonkey has a similar concept). They can’t have shared state, so in essence all … Read more
Unnamed semaphores are not supported, you need to use named semaphores. To use named semaphores instead of unnamed semaphores, use sem_open instead of sem_init, and use sem_close and sem_unlink instead of sem_destroy.
As suggested, use TPL Dataflow. A TransformBlock<TInput, TOutput> may be what you’re looking for. You define a MaxDegreeOfParallelism to limit how many strings can be transformed (i.e., how many urls can be downloaded) in parallel. You then post urls to the block, and when you’re done you tell the block you’re done adding items and … Read more
CountDownLatch is frequently used for the exact opposite of your example. Generally, you would have many threads blocking on await() that would all start simultaneously when the countown reached zero. final CountDownLatch countdown = new CountDownLatch(1); for (int i = 0; i < 10; ++ i) { Thread racecar = new Thread() { public void … Read more
Unfortunately everyone has missed the most important difference between the semaphore and the mutex; the concept of “ownership“. Semaphores have no notion of ownership, this means that any thread can release a semaphore (this can lead to many problems in itself but can help with “death detection”). Whereas a mutex does have the concept of … Read more
Any object in Java can be used as a lock using a synchronized block. This will also automatically take care of releasing the lock when an exception occurs. Object someObject = …; synchronized (someObject) { … } You can read more about this here: Intrinsic Locks and Synchronization
So, I am really confused about the significance of initial count? One important point that may help here is that Wait decrements the semaphore count and Release increments it. initialCount is the number of resource accesses that will be allowed immediately. Or, in other words, it is the number of times Wait can be called … Read more
In the kindergarden around the corner they use a SemaphoreSlim to control how many kids can play in the PE room. They painted on the floor, outside of the room, 5 pairs of footprints. As the kids arrive, they leave their shoes on a free pair of footprints and enter the room. Once they are … Read more
One difference is that SemaphoreSlim does not permit named semaphores, which can be system-wide. This would mean that a SemaphoreSlim could not be used for cross-process synchronization. The MSDN documentation also indicates that SemSlim should be used when “wait times are expected to be very short”. That would usually dovetail nicely with the idea that … Read more
Here is how I remember when to use what – Semaphore: Use a semaphore when you (thread) want to sleep till some other thread tells you to wake up. Semaphore ‘down’ happens in one thread (producer) and semaphore ‘up’ (for same semaphore) happens in another thread (consumer) e.g.: In producer-consumer problem, producer wants to sleep … Read more