Thread in Java

𝗧𝗵𝗿𝗲𝗮𝗱𝘀 in Java are a way to execute tasks concurrently within a program. A thread is essentially a path of execution within a program. When you create multiple threads, you can run several operations simultaneously, which is particularly useful for tasks involving I/O operations, such as file reading or network operations, or for improving the performance of applications that execute multiple independent tasks.

𝗞𝗲𝘆 𝗖𝗼𝗻𝗰𝗲𝗽𝘁𝘀 𝗮𝗯𝗼𝘂𝘁 𝗧𝗵𝗿𝗲𝗮𝗱𝘀 𝗶𝗻 𝗝𝗮𝘃𝗮

1. 𝗠𝗮𝗶𝗻 𝗧𝗵𝗿𝗲𝗮𝗱:

   • Every Java application starts with a single thread called the 𝙢𝙖𝙞𝙣 𝙩𝙝𝙧𝙚𝙖𝙙, which is automatically created by the JVM (Java Virtual Machine) when the program begins.

2. 𝗖𝗿𝗲𝗮𝘁𝗶𝗻𝗴 𝗧𝗵𝗿𝗲𝗮𝗱𝘀:
   There are two main ways to create threads in Java:

• 𝗘𝘅𝘁𝗲𝗻𝗱𝗶𝗻𝗴 𝘁𝗵𝗲 𝗧𝗵𝗿𝗲𝗮𝗱 𝗰𝗹𝗮𝘀𝘀: You can create a new class that extends Thread and overrides the run() method.

• 𝗜𝗺𝗽𝗹𝗲𝗺𝗲𝗻𝘁𝗶𝗻𝗴 𝘁𝗵𝗲 𝗥𝘂𝗻𝗻𝗮𝗯𝗹𝗲 𝗶𝗻𝘁𝗲𝗿𝗳𝗮𝗰𝗲: Another approach is to implement the 𝘙𝘶𝘯𝘯𝘢𝘣𝘭𝘦 interface and pass an instance of the class that implements 𝘙𝘶𝘯𝘯𝘢𝘣𝘭𝘦 to a Thread object.

1. 𝙧𝙪𝙣() 𝙖𝙣𝙙 𝙨𝙩𝙖𝙧𝙩() 𝙈𝙚𝙩𝙝𝙤𝙙𝙨:

   • The 𝚛𝚞𝚗() method contains the code that the thread will execute. When you call the 𝚜𝚝𝚊𝚛𝚝() method of a thread, it causes the JVM to create a new thread of execution and call the 𝚛𝚞𝚗() method in that new thread. If you call 𝚛𝚞𝚗() directly, it will run in the current thread without creating a new thread.

2. 𝗧𝗵𝗿𝗲𝗮𝗱 𝗦𝘁𝗮𝘁𝗲𝘀:

   • 𝗡𝗲𝘄: The thread has been created but not yet started.
   • 𝗥𝘂𝗻𝗻𝗮𝗯𝗹𝗲: The thread is ready to run but may be waiting for its turn to execute.
   • 𝗕𝗹𝗼𝗰𝗸𝗲𝗱: The thread is blocked waiting for a monitor lock.
   • 𝗪𝗮𝗶𝘁𝗶𝗻𝗴/𝗧𝗶𝗺𝗲𝗱 𝗪𝗮𝗶𝘁𝗶𝗻𝗴: The thread is waiting indefinitely or for a specified time until another thread notifies.
   • 𝗧𝗲𝗿𝗺𝗶𝗻𝗮𝘁𝗲𝗱: The thread has finished execution.

3. 𝗦𝘆𝗻𝗰𝗵𝗿𝗼𝗻𝗶𝘇𝗮𝘁𝗶𝗼𝗻:

   • When multiple threads access and modify shared data, race conditions can occur. To prevent this, Java offers the concept of s𝚢𝚗𝚌𝚑𝚛𝚘𝚗𝚒𝚣𝚊𝚝𝚒𝚘𝚗 using the 𝚜𝚢𝚗𝚌𝚑𝚛𝚘𝚗𝚒𝚣𝚎𝚍 keyword, which can be applied to methods or code blocks.

1. 𝗧𝗵𝗿𝗲𝗮𝗱 𝗖𝗼𝗺𝗺𝘂𝗻𝗶𝗰𝗮𝘁𝗶𝗼𝗻:

   • Java provides methods like 𝚠𝚊𝚒𝚝(), 𝚗𝚘𝚝𝚒𝚏𝚢(), and 𝚗𝚘𝚝𝚒𝚏𝚢𝙰𝚕𝚕() to allow threads to communicate with each other, especially useful for synchronizing threads in producer/consumer scenarios.

2. 𝗘𝘅𝗲𝗰𝘂𝘁𝗼𝗿𝘀 𝗮𝗻𝗱 𝗧𝗵𝗿𝗲𝗮𝗱 𝗣𝗼𝗼𝗹𝘀:

   • To manage a large number of threads, Java offers the java.util.concurrent framework, which includes classes like ExecutorService that facilitate the creation and management of thread pools.

1. 𝗧𝗵𝗿𝗲𝗮𝗱 𝗜𝗻𝘁𝗲𝗿𝗿𝘂𝗽𝘁𝗶𝗼𝗻:
   • You can request that a thread be interrupted by calling thread.interrupt(). The running thread should periodically check if it has been interrupted using the Thread.interrupted() or isInterrupted() methods.

𝗔𝗱𝘃𝗮𝗻𝘁𝗮𝗴𝗲𝘀 𝗮𝗻𝗱 𝗗𝗶𝘀𝗮𝗱𝘃𝗮𝗻𝘁𝗮𝗴𝗲𝘀

• 𝗔𝗱𝘃𝗮𝗻𝘁𝗮𝗴𝗲𝘀:

  • 𝗕𝗲𝘁𝘁𝗲𝗿 𝘂𝘀𝗲 𝗼𝗳 𝘀𝘆𝘀𝘁𝗲𝗺 𝗿𝗲𝘀𝗼𝘂𝗿𝗰𝗲𝘀: It can increase efficiency by utilizing multiple CPU cores.
  • 𝗜𝗺𝗽𝗿𝗼𝘃𝗲𝗱 𝗜/𝗢 𝗽𝗲𝗿𝗳𝗼𝗿𝗺𝗮𝗻𝗰𝗲: Threads can continue executing while an I/O operation is waiting.

• 𝗗𝗶𝘀𝗮𝗱𝘃𝗮𝗻𝘁𝗮𝗴𝗲𝘀:

  • 𝗖𝗼𝗺𝗽𝗹𝗲𝘅𝗶𝘁𝘆: Managing multiple threads can be complicated, especially when it comes to synchronization and communication.

  - 𝗦𝘆𝘀𝘁𝗲𝗺 𝗼𝘃𝗲𝗿𝗵𝗲𝗮𝗱: Creating and managing threads adds overhead to the system.

𝗥𝗮𝗰𝗲 𝗰𝗼𝗻𝗱𝗶𝘁𝗶𝗼𝗻𝘀 𝗮𝗻𝗱 𝗱𝗲𝗮𝗱𝗹𝗼𝗰𝗸𝘀: These are common issues in multi-threaded applications, requiring extra care in system design.

Threads are a powerful tool in Java for developing applications that require simultaneous task execution. However, improper use can lead to complex problems such as race conditions and deadlocks, necessitating a careful understanding of their implementation and management.