Thread Priorities

✅ What is Thread Priority?

• Every thread in Java has a priority, which helps the CPU decide which thread to run first.

• Priority is an integer value between 1 and 10.

• Higher priority means the thread is more likely to be chosen by the CPU — but it's not guaranteed.

📊 Priority Levels

1️⃣ Thread.MIN_PRIORITY

• It is a constant with value 1.

• Represents the lowest possible priority.

• Tells the JVM: "This thread is least important."

• Other higher-priority threads will get preference over this.

• Use it when the task is not urgent or can run in the background.

2️⃣ Thread.NORM_PRIORITY

• It is a constant with value 5.

• Represents the default (normal) priority for all threads.

• If you don’t manually set any priority, the thread runs with this.

• Balanced behavior — neither low nor high priority.

3️⃣ Thread.MAX_PRIORITY

• It is a constant with value 10.

• Represents the highest possible priority.

• Tells the JVM: "This thread is very important."

• JVM may give it more CPU time over other threads.

• Use it when the task is critical or time-sensitive.

🛠️ How to Set/Get Thread Priority

• Use setPriority(int) to assign a thread's priority.

• Use getPriority() to check it.

🧠 Example (just for understanding):

t1.setPriority(Thread.MAX_PRIORITY);   // Sets t1's priority to 10
int p = t1.getPriority();              // Gets the priority

⚠️ Important Notes

• CPU may or may not follow priorities strictly.

• Thread priority only gives a suggestion to the thread scheduler.

• On some platforms, all threads might behave as if they have the same priority.

You can set more than one thread with the same priority — whether it's Thread.MAX_PRIORITY, Thread.MIN_PRIORITY, or any value between 1 and 10.

✅ What Happens If Multiple Threads Have the Same Priority?

If multiple threads have the same priority, the JVM thread scheduler will use thread scheduling policies (like round-robin or time slicing) to decide which thread runs next.

🧠 Key Points:

• ✔️ You can set any number of threads to the same priority.

  Example:

  t1.setPriority(Thread.MAX_PRIORITY);
  t2.setPriority(Thread.MAX_PRIORITY);

• ⚙️ If two or more threads have equal priority, the order of execution is not guaranteed.

• 🕰️ The OS-level thread scheduler decides which thread gets CPU time — Java only suggests priority, it doesn't enforce it.

✅ Example Use Case

If two threads are ready to run:

• The one with higher priority is more likely to get CPU time first.

• But if the system is busy or platform doesn’t support it, both may run equally.

📝 Summary