Java.Multithreading.Can i adjust ThreadPoolExeccutor to work on different cores ?

❓ Can you adjust ThreadPoolExecutor to run on different cores?

⚠️ Short Answer: Not directly in Java — you cannot manually bind threads to specific cores using ThreadPoolExecutor or Java alone.

But…

✅ Long Answer: You can influence it indirectly and even hack it a bit if you’re determined 😎

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🧠 Why Not Directly?

The JVM does not expose APIs to set CPU affinity (i.e., bind a thread to a specific core).

The actual thread scheduling (which thread runs on which core) is done by the operating system, not by Java.

So even if you create multiple threads:

ExecutorService pool = Executors.newFixedThreadPool(4);

➡️ The JVM says, “Here are 4 threads.”
➡️ The OS scheduler decides where to run them (and it might even migrate them between cores).

✅ How Can You Indirectly Influence Core Usage?

1. Use Runtime.getRuntime().availableProcessors()
   Create a thread pool with one thread per core:

int cores = Runtime.getRuntime().availableProcessors();
ExecutorService pool = Executors.newFixedThreadPool(cores);

📌 This matches thread count to CPU cores, increasing your chances of real parallelism.

Do CPU-bound work (not I/O)
OS is more likely to spread CPU-intensive threads across multiple cores, especially if they’re all actively using the CPU.

Keep threads busy long enough
If your tasks are short-lived, the OS may just queue them on one core.
But longer tasks give the OS time to distribute them better.

🧪 Want to Force Core Affinity?

This is possible, but requires native tricks:

🧰 Option A: Use JNI or JNA

You can use sched_setaffinity on Linux or SetThreadAffinityMask on Windows:

• JNI (Java Native Interface): Write C/C++ code to bind threads
• JNA (Java Native Access): Use native libraries from Java directly

Example in C for Linux:

cpu_set_t mask;
CPU_ZERO(&mask);
CPU_SET(0, &mask);
sched_setaffinity(0, sizeof(mask), &mask);

Use JNA to call this from Java.

🧠 Libraries like Jaffinity or Taskset in Linux can help too.

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💡 TL;DR Summary

Approach	Can control core usage?
Default Java ThreadPoolExecutor	❌ No (OS decides)
Matching threads to core count	✅ Helps indirectly
JNI/JNA + native affinity APIs	✅ Yes (low-level hack)
ForkJoinPool	✅ OS uses more cores, but still not guaranteed