JVM의 가상 스레드 메커니즘에서 고정 탐색

Java's virtual threads offer a lightweight alternative to traditional OS threads, enabling efficient concurrency management. But understanding their behavior is crucial for optimal performance. This blog post dives into pinning, a scenario that can impact virtual thread execution, and explores techniques to monitor and address it.

Virtual Threads: A Lightweight Concurrency Approach

Java's virtual threads are managed entities that run on top of the underlying operating system threads (carrier threads). They provide a more efficient way to handle concurrency compared to creating numerous OS threads, as they incur lower overhead. The JVM maps virtual threads to carrier threads dynamically, allowing for better resource utilization.

• Managed by the JVM: Unlike OS threads that are directly managed by the operating system, virtual threads are created and scheduled by the Java Virtual Machine (JVM). This allows for finer-grained control and optimization within the JVM environment.

• Reduced Overhead: Creating and managing virtual threads incurs significantly lower overhead compared to OS threads. This is because the JVM can manage a larger pool of virtual threads efficiently, utilizing a smaller number of underlying OS threads.

• Compatibility with Existing Code: Virtual threads are designed to be seamlessly integrated with existing Java code. They can be used alongside traditional OS threads and work within the familiar constructs like Executor and ExecutorService for managing concurrent.

The figure below shows the relationship between virtual threads and platform threads:

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Pinning: When a Virtual Thread Gets Stuck

Pinning occurs when a virtual thread becomes tied to its carrier thread. This essentially means the virtual thread cannot be preempted (switched to another carrier thread) while it's in a pinned state. Here are common scenarios that trigger pinning:

• Synchronized Blocks and Methods: Executing code within a synchronized block or method leads to pinning. This ensures exclusive access to shared resources, preventing data corruption issues.

Code Example:

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class Main {

  public static void main(String[] args) throws InterruptedException {

    final Counter counter = new Counter();

    Runnable task = () -> {
      for (int i = 0; i be3c6ba0a699aca98d67df8bee3b84fd {
      for (int i = 0; i 4596771306681ecdae85c561b8883cd6 {
      for (int i = 0; i < 100; i++) {
        counter.increment();
      }
    };

    Thread thread1 = Thread.ofVirtual().start(task);
    Thread thread2 = Thread.ofVirtual().start(task);

    try {
      thread1.join();
      thread2.join();
    } catch (InterruptedException e) {
      throw new RuntimeException(e);
    }

    System.out.println("Final counter value: " + counter.getCount());
  }
}

class Counter {

  private int count = 0;
  private final ReentrantLock lock = new ReentrantLock();

  public void increment() {
    lock.lock();
    try {
      Thread.sleep(100); // This simulates a blocking call
      count++;
    } catch (InterruptedException e) {
      e.printStackTrace();
    } finally {
      lock.unlock();
    }
  }

  public int getCount() {
    return count;
  }
}

In the updated example, we use a ReentrantLock instead of a synchronized block. The thread can acquire the lock and release it immediately after it completes its operation, potentially reducing the duration of pinning compared to a synchronized block which might hold the lock for a longer period.

결론적으로

Java의 가상 스레드는 언어의 진화와 기능에 대한 증거입니다. 이는 기존 OS 스레드에 대한 새롭고 가벼운 대안을 제공하여 효율적인 동시성 관리를 위한 다리를 제공합니다. 스레드 고정과 같은 핵심 개념을 깊이 파고들고 이해하는 데 시간을 투자하면 개발자는 이러한 경량 스레드의 잠재력을 최대한 활용할 수 있는 노하우를 얻을 수 있습니다. 이러한 지식은 개발자가 향후 기능을 활용할 수 있도록 준비할 뿐만 아니라 현재 프로젝트에서 복잡한 동시성 제어 문제를 보다 효과적으로 해결할 수 있도록 지원합니다.

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