In Java programming,Blocking method(blocking methods) refer to methods in which the current thread pauses execution until some conditions are met or events occur. In this case, the current thread enters a blocking state and does not occupy CPU resources, but cannot perform any other operations until the method is completed or the condition is met.
1. Characteristics of blocking method
The blocking method usually has the following characteristics:
- Pause thread execution: The thread calling the blocking method will be suspended and enter the blocking state until the method returns or the condition is satisfied.
- No CPU resources: Threads in blocked state do not consume CPU time slices, so they do not cause direct burden on system performance, but it prevents threads from performing other tasks.
- Depend on external conditions: The blocking method usually waits for some external condition or event, such as the completion of I/O operation, lock release, thread wakeup, etc.
- Potential impact: If not properly handled, the blocking method may cause the thread to be in a waiting state for a long time, which will affect the application's responsiveness and concurrency performance.
2. Common blocking methods in Java
In Java, there are many common blocking methods, which are often found in multithreaded programming, I/O operations, and network programming.
2.1 ()
(long millis)is a blocking method used to make the current thread sleep the specified number of milliseconds. During this time, the thread is blocked and no operations are performed until the specified time has elapsed.
public class SleepExample {
public static void main(String[] args) {
("Thread is going to sleep...");
try {
(2000); // Thread sleeps for 2 seconds } catch (InterruptedException e) {
();
}
("Thread woke up!");
}
}
In this example,(2000)Block the current thread for 2 seconds, and then continue execution.
2.2 ()
()is a blocking method that causes the current thread to enter a waiting state until other threads callnotify()ornotifyAll()Method to wake it up. Usually used for synchronization and communication between threads.
public class WaitNotifyExample {
private static final Object lock = new Object();
public static void main(String[] args) {
Thread waitingThread = new Thread(() -> {
synchronized (lock) {
try {
("Thread is waiting...");
(); // The thread enters a waiting state ("Thread is resumed!");
} catch (InterruptedException e) {
();
}
}
});
Thread notifyingThread = new Thread(() -> {
synchronized (lock) {
("Thread is notifying...");
(); // Wake up the waiting thread }
});
();
try {
(1000); // Make sure waitingThread enters the waiting state } catch (InterruptedException e) {
();
}
();
}
}
In this example,wait()Method to makewaitingThreadEnter the waiting state untilnotifyingThreadCallnotify()Method to wake it up.
2.3 ()
()is a blocking method that allows the current thread to wait for another thread to complete execution before continuing. For example, if called in the main thread(), the main thread will be blocked until the threadtThe operation is completed.
public class JoinExample {
public static void main(String[] args) {
Thread t = new Thread(() -> {
try {
(2000);
("Thread finished execution");
} catch (InterruptedException e) {
();
}
});
();
try {
(); // The main thread waits for the t thread to complete } catch (InterruptedException e) {
();
}
("Main thread continues after t finishes");
}
}
In this example,()Block the main thread untiltThe thread is executed.
2.4 Blocking method in I/O operation
In Java, I/O operations (such as file reading and writing, network communication) are usually blocked. For example,()Methods block the current thread when there is no data available for reading until the data is available or reaches the end of the stream.
import ;
import ;
public class FileReadExample {
public static void main(String[] args) {
try (FileInputStream fis = new FileInputStream("")) {
int data;
while ((data = ()) != -1) { // read() is a blocking method ((char) data);
}
} catch (IOException e) {
();
}
}
}
In this example,()The method will block until the end of the data or file is read.
2.5 Blocking methods in network programming
In network programming,()、()The methods such as this are also blocking. For example,()The method will block the current thread until a client connects to the server.
import ;
import ;
import ;
public class ServerSocketExample {
public static void main(String[] args) {
try (ServerSocket serverSocket = new ServerSocket(8080)) {
("Server is listening on port 8080...");
Socket clientSocket = (); // accept() is a blocking method ("Client connected: " + ());
} catch (IOException e) {
();
}
}
}
In this example,()The method will block until a client connects to the server.
3. Advantages and disadvantages of blocking methods
advantage
- Simple and easy to use: The logic of the blocking method is simple and easy to understand, and developers do not need to deal with complex asynchronous logic or callbacks.
- Easy resource management: Since blocking methods usually do not frequently occupy CPU resources, they are more efficient when handling I/O operations.
- Natural control flow: The blocking method follows a natural control flow, the code is more intuitive and does not require separate processing logic.
shortcoming
- Potential performance issues: If the thread is blocked for a long time, it will cause the threads in the thread pool to be occupied, which may lead to the application's response ability drop or deadlock.
- May cause thread hunger: In a multi-threaded environment, long-term blocking may cause other threads to fail to obtain execution opportunities, which in turn causes thread hunger problems.
- Not suitable for high concurrency scenarios: In high concurrency applications, too many blocking methods may cause a surge in the number of threads, increasing the overhead of memory and thread context switching.
4. Alternatives: Non-blocking methods and asynchronous programming
Due to the inherent shortcomings of blocking methods, especially in systems with high concurrency and real-time requirements, non-blocking methods or asynchronous programming models are often considered.
4.1 Non-blocking I/O
The Java NIO (New I/O) library introduces non-blocking I/O, allowing threads to continue performing other tasks when no data is available. Through the selector model, one thread can manage operations of multiple I/O channels, thereby improving concurrency performance.
import ;
import .*;
import ;
public class NonBlockingServerExample {
public static void main(String[] args) throws IOException {
Selector selector = ();
ServerSocketChannel serverSocketChannel = ();
(new InetSocketAddress(8080));
(false);
(selector, SelectionKey.OP_ACCEPT);
while (true) {
();
for (SelectionKey key : ()) {
if (()) {
ServerSocketChannel server = (ServerSocketChannel) ();
SocketChannel client = ();
(false);
(selector, SelectionKey.OP_READ);
("Connected to client: " + ());
}
// Handle other operations like OP_READ, OP_WRITE
}
().clear();
}
}
}
4.2 Asynchronous Programming Model
Java'sCompletableFutureProvides powerful asynchronous programming support. passCompletableFuture, you can handle asynchronous tasks in non-blocking situations.
import ;
public class CompletableFutureExample {
public static void main(String[] args) {
(() -> {
try {
(2000); // Simulate long-term operation } catch (InterruptedException e) {
();
}
return "Result after 2 seconds";
}).thenAccept(result -> {
("Received: " + result);
});
("Main thread continues...");
}
}
In this example, the asynchronous task is running in the background, and the main thread does not have to wait for it to complete and can continue to perform other operations.
5. Summary
The blocking method is a common way to handle thread synchronization, I/O operations and network communication in Java programming. Although they are easy to use, blocking methods can lead to performance bottlenecks in applications with high concurrency and performance requirements. Therefore, developers need to weigh the use of blocking methods versus non-blocking methods or asynchronous programming models based on specific application scenarios.
- Advantages of blocking methods: Simple and easy to use, suitable for handling tasks executed sequentially.
- Disadvantages of blocking methods: Performance problems may occur in systems with high concurrency or high real-time requirements.
-
Non-blocking vs. asynchronous alternatives: Java NIO and
CompletableFutureProvides a more efficient solution for scenarios where a large number of concurrent tasks are required.
By understanding the working principle of the blocking method and its applicable scenarios, developers can better design and optimize Java applications to meet the performance needs in different scenarios.
This is the end of this article about Java implementing thread blocking methods. For more related Java thread blocking content, please search for my previous articles or continue browsing the related articles below. I hope everyone will support me in the future!