What is the relationship between threads (in a Java or a C++ program) and number of cores in the CPU?

Question

Can someone shed some light on it?

An i7 processor can run 8 threads but I am pretty sure we can create more than 8 threads in a JAVA or C++ program(not sure though). I have an i5 processor and while studying concurrency I have created 10 threads for assignments. I am just trying to understand how Core rating of CPU is related to threads.

Answer 1

The thread you are refering to is called a software thread; and you can create as many software threads as you need, as long as your operating system allows it. Each software thread, or code snippet, can run concurrently from the others.

For each core, there is at least one hardware thread to which the operating system can assign a software thread. If you have 8 cores, for example, then you have a hardware thread pool of capacity 8. You can map tens or hundreds of software threads to this 8-slot pool, where only 8 threads are actually running on hardware at the same time, i.e. in parallel.

Software threads are like people sharing the same computer. Each one can use this computer up to some time, not necessarily have his task completed, then give it up to another.

Hardware threads are like people having a computer for each of them. All of them can proceed with their tasks at the same time.

Note: For i7, there are two hardware threads (so called hyper-threading) in each core. So you can have up to 16 threads running in parallel.