Threads Summary

Thread Concept

• Unit of program execution
• Independent sequence of operations
• Can run concurrently
• Example:

  Thread t = new Thread(() -> {
    System.out.println("Running in new thread");
  });
  t.start();
  

Creating Threads

1. Using Runnable:

   Runnable task = () -> {
     // task code here
   };
   Thread thread = new Thread(task);
   thread.start();
   

2. Extending Thread:

   class MyThread extends Thread {
     public void run() {
       // task code here
     }
   }
   new MyThread().start();
   

Thread States

• NEW: Created but not yet started
• RUNNABLE: Executing or ready to execute
• BLOCKED: Waiting for monitor lock
• WAITING: Waiting indefinitely
• TIMED_WAITING: Waiting for specified time
• TERMINATED: Completed execution

Thread Operations

1. Basic Operations:

   thread.start();     // start thread
   thread.join();      // wait for completion
   thread.sleep(1000); // pause execution
   thread.interrupt(); // interrupt thread
   

2. Thread Information:

   Thread.currentThread().getName();    // get name
   Thread.currentThread().isAlive();    // check if alive
   Thread.currentThread().setPriority(5); // set priority
   

Thread Safety Issues

1. Race Conditions:

   // Unsafe
   counter++;  // not atomic
   
   // Safe
   synchronized(lock) {
     counter++;
   }
   

2. Visibility Problems:

   // May have visibility issues
   boolean flag = false;
   
   // Guaranteed visibility
   volatile boolean flag = false;
   

Best Practices

• Use thread pools when possible
• Handle interruptions properly
• Avoid shared mutable state
• Use proper synchronization
• Document thread safety
• Test concurrent behavior
• Example: ```java try { thread.join(); } catch (InterruptedException e) { Thread.currentThread().interrupt(); // handle interruption }