Wei Lai: what is the difference between multithreaded join and detach?

1、 Rendezvous （joinable）： In this relationship , The main thread needs to explicitly perform the wait operation , After the child thread ends , The waiting operation of the main thread is completed , The child thread meets the main thread , At this time, the main thread continues to perform the next operation after the wait operation . The main thread must rendezvous with renderable child threads . Call the function of the child thread object inside the thread function of the main thread wait Function implementation , Even if the child thread can finish executing before the main thread , Into the termination state , The rendezvous operation must also be performed , otherwise , The system will never actively destroy threads , The system resources allocated to the thread will never be released .

2、 phase separation （detached）： Indicates that the child thread does not need to meet with the main thread , That is, phase separated , In this case , Once the child thread enters the termination state , This method is often used when there are many online processes , Sometimes the main thread is asked to wait one by one for the sub thread to end , Or let the main thread arrange the waiting order for the end of each sub thread , It is difficult or impossible , So when there are many concurrent sub threads , This method is also often used .

At any point in time , Threads are associative （joinable） Or separable （detached）, A combinable thread can be recycled and killed by other threads , Before being recycled by other threads , Its memory resources, such as stack , It's not released , contrary , A detached thread cannot be recycled or killed by other threads , Its memory resources are automatically released by the system when it terminates .

The state of thread separation determines how a thread terminates itself , By default , Threads are non detached , In this case , The original thread waits for the created thread to finish , Only when pthread_join When function returns , The thread created is terminated , Release the system resources occupied by yourself , The detached thread is not waiting by other threads , It's over , The thread is terminated , Release system resources now .