[concurrent programming] concurrent tool class of thread

Fork-Join

Divide and conquer algorithm （ Divide and rule ）

The scale is N The problem of ,N< threshold , Direct solution ,N> threshold , take N Decompose into K A small mold problem , The subproblems are independent of each other , The same form as the original problem , The solutions of the subproblem are combined to obtain the solution of the original problem

Dynamic specifications

Working secret

workStealing

Fork/Join The standard paradigm used

Common concurrent tool classes

CountDownLatch

effect ： It is a group of threads that wait for other threads to complete their work before executing , Enhanced Edition join

await To wait for (join),countDown Take charge of the subtraction of the counter

CyclicBarrier

Let a group of threads reach a barrier , Blocked , Until the last thread in the group reaches the barrier , The barrier is open , All blocked threads will continue to run CyclicBarrier(int parties)

await It can be used repeatedly

CyclicBarrier(int parties, Runnable barrierAction), The barrier is open ,barrierAction The defined task will execute

CountDownLatch and CyclicBarrier Differentiation and analysis

1、countdownlatch Controlled by the third party ,CyclicBarrier Release is controlled by a set of threads themselves
2、countdownlatch Release conditions >= Number of threads ,CyclicBarrier Release conditions = Number of threads

Semaphore

Control the number of threads accessing a specific resource at the same time , Used in flow control

useful.acquire();                    synchronized (pool) {                             conn = pool.removeFirst();                    }                    useless.release();

Exchange

Data exchange between two threads

Callable、Future and FutureTask

isDone, end , Normal or abnormal end , Or cancel it yourself , return true;

isCancelled The task was canceled before it was completed , return true;

cancel（boolean）：

1. The task hasn't started yet , return false
2. The mission has started ,cancel（true）, Interrupt a running task , Interrupt success , return true,cancel（false）, Don't interrupt the running tasks
3. The task is over , return false

Processing of documents containing pictures and words ： picture （ On the cloud ）, It can be used future Go get the picture , The main thread continues to parse the text .