[concurrent programming] collaboration between threads

 2022.02.09

Collaboration between threads

polling ： It is difficult to guarantee timeliness , Resources are expensive ,

Waiting and notifying

wait()    Method on object

notify/notifyAll  Method on object

The standard paradigm for waiting and notification

Waiting party ：

1. Get the lock of the object ;
2. In the cycle, judge whether the conditions are satisfied , Not satisfied with call wait Method ,
3. Conditions meet to execute business logic

The informer said

1. 1. Get the lock of the object ;
   2. Change the conditions
   3. Notify all threads waiting on the object

notify and notifyAll Who should I use ？

Should be used as much as possible notifyAll, Use notify Because there may be signal loss

Wait timeout mode implements a connection pool

hypothesis   The waiting time is T, current time now+T After that, it's time-out

long  overtime = now+T;

long remain = T;// The duration of the wait 

while(result Not meeting the conditions && remain>0){

       wait(remain);

       remain = overtime – now;// Wait for the remaining duration 

}

return result;

join() Method

Threads A, Thread executed B Of join Method , Threads A You have to wait B When the execution is complete , Threads A To continue your work

call yield() 、sleep()、wait()、notify() What are the effects of methods such as ？

yield()\sleep() Does not release the lock , Just get out of the way cpu The enforcement of

Thread executing yield() in the future , The lock held is not released

sleep() When the method is called , The lock held is not released

Before the transfer method , You have to hold the lock . Called wait() After method , The lock will be released , When wait When the method returns , The thread will hold the lock again

Before the transfer method , You have to hold the lock , call notify() The method itself does not release the lock