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There are many places across the web and Stack Overflow where one is discouraged from changing the priority of a ThreadPool thread or TPL Task. In particular:
However, it is a simple matter to do so, and the debugger shows that the change does seem to stick (insofar as the value can be read back).
Thread.CurrentThread.Priority = ThreadPriority.AboveNormal; So the question is, what is the specific reason for this particular taboo?
My suspicion: doing so disturbs the delicate load balancing-assumptions of the pool. But this doesn't explain why some sources say that you can't change it.
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Thread priority does not guarantee execution order. It comes into play when resources are limited. If the System is running into constraints due to memory or CPU, then the higher priority threads will run first.
The thread priority determines when the processor is provided to the thread as well as other resources. It can be changed using the method setPriority() of class Thread. There are three static variables for thread priority in Java i.e. MIN_PRIORITY, MAX_PRIORITY and NORM_PRIORITY.
Thread pools do not make sense when you need thread which perform entirely dissimilar and unrelated actions, which cannot be considered "jobs"; e.g., One thread for GUI event handling, another for backend processing. Thread pools also don't make sense when processing forms a pipeline.
By default, TPL types like Task and Task<TResult> use thread pool threads to run tasks. You can also use the thread pool by calling ThreadPool.
The by default priority of a thread is Normal. Operating system does not assign the priority of threads. If a thread has reached a final state, such as Aborted, then this will give ThreadStateException. If the value specified for a set operation is not a valid ThreadPriority value, then this will give ArgumentException
The System.Threading.ThreadPool class provides your application with a pool of worker threads that are managed by the system, allowing you to concentrate on application tasks rather than thread management. If you have short tasks that require background processing, the managed thread pool is an easy way to take advantage of multiple threads.
In most cases, the thread scheduler schedules the threads according to their priority (known as preemptive scheduling). But it is not guaranteed because it depends on JVM specification that which scheduling it chooses.
We know that a thread with high priority will get preference over lower priority threads when it comes to the execution of threads. However, there can be other scenarios where two threads can have the same priority. All of the processing, in order to look after the threads, is done by the Java thread scheduler.
The thread pool, especially the .NET 4.0 thread pool, has many tricks up its sleeve and is a rather complicated system. Add in tasks and task schedulers and work stealing and all sorts of other things and the reality is you don't know what is going on. The thread pool may notice that your task is waiting on I/O and decide to schedule something quick on your task or suspend your thread to run something of higher priority. Your thread may somehow be a dependency for a higher-priority thread (that you may or may not be aware of) and end up causing a deadlock. Your thread may die in some abnormal way and be unable to restore priority.
If you have a long-running task such that you think it would be best that your thread have a lower priority then the thread pool probably isn't for you. While the algorithms have been improved in .NET 4.0, it is still best used for short-lived tasks where the cost of creating a new thread is disproportional to the length of the task. If your task runs for more than a second or two the cost of creating a new thread is insignificant (although management might be annoying).
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I've done some experimentation with a reduced-size thread pool which seems to indicate that the thread's priority is reset back to normal once returned to the pool. This resource on threading seems to confirm it. So the effect seems to be very limited even if you do.
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