Maximum number of threads than can run concurrently in java on a CPU

Question

Please I got confused about something. What I know is that the maximum number of threads that can run concurrently on a normal CPU of a modern computer ranges from 8 to 16 t

Answer 1

At any given time, a processor will run the number of threads equal to the number of cores contained. This means that on a uniprocessor system, only one thread (or no thread) is being run at any given moment.

However, processors do not run each thread one after another, rather they switch between multiple threads rapidly to simulate concurrent execution. If this weren't the case let alone create multiple threads, you won't even be able to start multiple applications.

A java thread (compared to processor instructions) is a very high level abstraction of a set of instructions for the CPU to process. When it gets down to the processor level, there is no guarantee which threads will run on which core at any given time. But given that processors rapidly switch between these threads, it is theoretically possible to create an infinite amount of threads albeit at the cost of performance.

If you think about it, a modern computer has thousands of threads running at the same time (combining all applications) while only having 1 ~ 16 (typical case) number of cores. Without this task-switching, nothing would ever get done.

If you are optimizing your application, you should consider the amount of threads you need by the work at hand, and not by the underlying architecture. Performance gains from parallelism should be weighted against increasing overheads of thread execution. Since every machine is different, every runtime environment is different, it is impractical to work out some golden thread count (however, a ballpark estimate may be made by benchmarking and looking at number of cores).