This is okay, as long as the calling thread is not a threadpool thread. The execution is wrapped inside a Task.Run, this will schedule the task on the threadpool the block the calling thread. Problem solved.īut, it turns out that you need to implement a sync interface and you are supposed to implement using API which has async only functions. In an operating system, a deadlock occurs when a process or thread enters a waiting state because a requested system resource is held by another waiting process. The problem can be avoided altogether by making the method async as well. A Java multithreaded program may suffer from the deadlock condition because the synchronized keyword causes the executing thread to block while waiting for the lock, or monitor, associated with the specified object. The problem the developer is facing that the API they are supposed to call is async only, but the function they are implementing is sync. Deadlock occurs when multiple threads need the same locks but obtain them in a different order.
Deadlock programming code#
I wrote code like this that’s how I know it deadlocks. It doesn’t matter who wrote it, anyone could have written this. Try to guess the intent, the reason why it’s written like this. The proper async / await version: public async Task DownloadStringV1(String url) This does not use much CPU, so to use resources efficiently we use the async methods of HttpClient. The application needs to request some data from a server. This is how you would properly implement an I/O bound operation. Threads execute Tasks which as scheduled by a TaskScheduler. The whole picture looks look something like this: So Threads execute Tasks… simple you might think… but that’s not the whole picture. For performance reasons there is usually more than one thread. In C# each thread also has an associated SynchronizationContext which is used to communicate between different types of threads.Ĭ# uses Threads to run some code and mark some Tasks as being completed. Threads have a call stack, store local variables, and the address of the currently executing instruction. Threads keep track what you execute and where you execute. Threads just as in any OS represent execution of code. Threads are a completely different story. Tasks have an associated TaskScheduler which is used to schedule a continuation Task, or any other child Tasks that are required by the current Task. Faulted state means that there was an exception. If the Task is completed and not faulted then the continuation task will be scheduled. This is the only thing that a Task does, it keeps track whether a some work has been completed or not. A Task can be faulted just like how a Promise can be rejected. A Task can be completed just like how a Promise can be fulfilled. The equivalent in some many languages is the Promise. The moment when it completes can be right now or in the future. Task represents some work that needs to be done. They are two separate concepts and should be treated as such. Task does not belong to a Thread or anything like that. Task does not guarantee parallel execution. Tasks have nothing to do with Threads and this is the cause of many misconceptions, especially if you have in your might something like “well a Task is like a lightweight Thread”.
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