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1. Executors
Executors class belongs to java.util. Concurrent package;
Create a thread pool by following two methods: ThreadPoolExecutor and Executors;
Exector (Static Executor Factory) creates a thread pool.
Factory and tool methods Executor, ExecutorService, ScheduledExecutorService, ThreadFactory, and Callable classes defined in this package;
The jdk1.8API explains as follows:
2. Executors Structure
3. Common methods for Executors
Public static ExecutorService newFixedThreadPool(int nThreads) A thread pool with a fixed number of threads. When threads are idle, they are not recycled unless the pool is closed. When all threads are active, new tasks wait until a thread is free.
Public static ExecutorService newSingleThreadExecutor() creates a single thread. It applies to tasks that need to be executed sequentially; And no more than one thread is active at any point in time. If a thread dies, a thread is restarted to continue executing the task.
Public static ExecutorService newCachedThreadPool() creates a thread pool that creates new threads as needed, but recycles previously constructed threads as they become available, or creates a new thread and adds it to the pool if there are no available threads. Threads that are not used for 60 seconds are terminated and removed from the cache; Threads are created when they are used and destroyed when they are not used.
- Public static ScheduledExecutorService newScheduledThreadPool(int corePoolSize) Creates a thread pool that can schedule commands to run after a given delay or to execute them periodically. Supports the execution of scheduled or periodic tasks.
Create a thread pool that maintains enough threads to support a given level of parallelism. And you can use multiple queues to reduce contention. (New method in JDK1.8)
4. Create a thread pool in two ways (use Executors to create a thread pool).
1. Example newFixedThreadPool method
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The following figure shows the output
Conclusion: In the example, a fixed number of 3 threads are created. As shown in the screenshot of the output result, the number of iterations is 5. After a round of execution (3 times), the execution is paused for one second until a thread is free, and the fourth execution is continued.
2. Example newSingleThreadExecutor method
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The following figure shows the output
Conclusion: The example creates a single thread that sleeps for one second after each task to ensure that the tasks are executed sequentially.
The newCachedThreadPool method
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The following figure shows the output
Conclusion: In the example, thread pools with cached threads are created as needed and previously constructed threads are reused when available.
4. Example newScheduledThreadPool method
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The following figure shows the output
Conclusion: In the example, a thread pool is created to execute periodic or scheduled tasks. Based on the output, the task takes effect one minute later.
Executors Create a thread pool
The ThreadPoolExecutor constructor is called whenever a thread pool of any type is created (newFixedThreadPool, newSingleThreadExecutor, newCachedThreadPool, and so on).
Parsing arguments in the ThreadPoolExecutor constructor
CorePoolSize Specifies the maximum number of core threads in a thread pool.
MaximumPoolSize Specifies the maximum number of threads (both core and non-core) running in the thread pool.
KeepAliveTime The maximum length of time an idle thread (non-core thread only) can live in the thread pool;
Unit Unit of keepAliveTime. Used with keepAliveTime.
WorkQueue Stores the blocking queue of tasks.
Handler Thread pool saturation policy.
Understanding the Executor interface
Executor belongs to the java.util.concurrent package;
Executor is the core interface of the task execution mechanism;
Executor interface class diagram structure
According to the structure of the class diagram,
ThreadPoolExecutor inherits the AbstractExecutorService interface;
The AbstractExecutorService interface implements the ExecutorService interface.
ExecutorService inherits the Executor interface;
So the following sections focus on the ThreadPoolExecutor class.
Common Executor interface methods
Void execute(Runnable command) Executes a given command at a future time. This command can be executed in a new thread, a merged thread, or in the calling thread, implemented by Executor.
There are two ways to create a thread pool (ThreadPoolExecutor).
Constructor in ThreadPoolExecutor class
public ThreadPoolExecutor(int corePoolSize, int maximumPoolSize,long keepAliveTime,TimeUnit unit,BlockingQueue workQueue,defaultHandler)
ThreadPoolExecutor constructor parameter parsing
CorePoolSize Specifies the maximum number of core threads in a thread pool.
MaximumPoolSize Specifies the maximum number of threads (both core and non-core) running in the thread pool.
KeepAliveTime The maximum length of time an idle thread (non-core thread only) can live in the thread pool;
Unit Unit of keepAliveTime. Used with keepAliveTime.
WorkQueue Stores the blocking queue of tasks.
Handler Thread pool saturation policy.
Example ThreadPoolExecutor class to create a thread pool
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The following figure shows the output
Conclusion: The ThreadPoolExecutor constructor is called regardless of the type of thread pool you create (newFixedThreadPool, newSingleThreadExecutor, newCachedThreadPool, and so on).
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