wait

Out of curiosity, when Java implements wait() and notify() methods, are they really just using locks? i.e., wait() acquires a mutex, notify() release a mutex, notifyAll() releases all mutexes (in the same object, of course)? Other than being less cumbersome than using locks, are there other advantages of using wait() and notify()? [EDIT] I realized what I confused myself about after Brian's comments: wait doesn't lock, it releases the lock and passes it to someone else who's waiting on a synchronized statement for the mutex, then waits to be notified by someone else who has the lock and calls

I have this line in my code : t = wait(&status); When the child process works, the value of status is 0, well. But why does it return 256 when it doesn't work? And why changing the value of the argument given to exit in the child process when there is an error doesn't change anything (exit(2) instead of exit(1) for example)? Thank you Edit : I'm on linux, and I compiled with GCC. I defined status like this int status; t = wait(&status); Given code like this... int main(int argc, char **argv) { pid_t pid; int res; pid = fork(); if (pid == 0) { printf("child\n"); exit(1); } pid = wait(&res);

在学习go语言时,用到了“sync”包中的WaitGourp结构,来达到控制任务的完成。 由于WaitGroup是结构，所有需要通过 sync.WaitGroup{} 来创建 很类似与 Shoper/JAVA并发库之倒记时锁存器CountDownLatch 中的CountDownLatch类。 Add()，Done()，Wait()。其中Done()是Add(-1)的别名。简单的来说，使用Add()添加计数，Done()减掉一个计数，计数不为0, 阻塞Wait()的运行。 package main import ( "fmt" "runtime" "sync" ) func main() { runtime.GOMAXPROCS(runtime.NumCPU()) waitGourp := sync.WaitGroup{} waitGourp.Add(10) for i := 0; i < 10; i++ { go Go(&waitGourp, i) } waitGourp.Wait() } func Go(wg *sync.WaitGroup, index int) { sum := 0 for i := 0; i < 100000000; i++ { sum += i } fmt.Println(index, sum) wg.Done() } PS：由于之前用的是java

sync.WaitGroup的错误用法与纠正 本文主要是记录在学习golang语言过程中错误使用sync.WaitGroup以及指针引起的报错，并且纠正过程。 1.错误使用场景 main包的实现内容： package main import ( "fmt" "pressure/game" "sync" ) var waitGroup sync.WaitGroup //定义一个同步等待的组 func main(){ waitGroup.Add (1 ) //添加一个计数 go game.ConnSocket(serverAddr, waitGroup) //调用其他包的方法执行任务 waitGroup.Wait() //阻塞直到所有任务完成 fmt.Println( "main DONE!!!" ) } 如下是game包的内容： package game import ( "fmt" "net" "strconv" "strings" "sync" ) var gameWait sync.WaitGroup func ConnSocket(serverAddr string , wait sync.WaitGroup) { var err error Conn, err = net.Dial( "tcp" , serverAddr) if err != nil { fmt

源码使用的是1.9版本；sync 包里的WaitGroup主要用于线程的同步；计数主线程创建的子线程（WaitGoup.Add(i)）;调用清除标记方法（WaitGroup.Done()）;使用WaitGroup.Wait()来阻塞，直到所有子线程（标记=0）执行完毕。 例子： package main import ( "sync" "fmt" ) func main(){ var swg sync.WaitGroup for i: =0 ;i <3 ;i++{ //增加一个计数器 swg.Add (1 ) go func (wg *sync.WaitGroup,mark int ){ //减去计数器 defer wg.Done() //等价于 wg.Add(-1) fmt.Printf( "%d goroutine finish \n" ,mark) }(&swg,i) } //等待所有go程结束 swg.Wait() } 结果： 2 goroutine finish 1 goroutine finish 0 goroutine finish 注意！如果将代码改成下面这样（子线程函数，传入的参数是waitgroup的值拷贝），会出现什么情况呢？ func main(){ var swg sync.WaitGroup for i: =0 ;i <3 ;i++{ swg.Add

I am looking in some puzzles for threads and I can't figure out why the following consistently prints 999999 : class Job extends Thread { private Integer number = 0; public void run() { for (int i = 1; i < 1000000; i++) { number++; } } public Integer getNumber() { return number; } } public class Test { public static void main(String[] args) throws InterruptedException { Job thread = new Job(); thread.start(); synchronized (thread) { thread.wait(); } System.out.println(thread.getNumber()); } } There is no notify on the same lock (and spurious wakeup seem to be ignored). If a thread finishes

I have a 500,000 line SQL script: update users set region_id = 9814746 where id = 101 and region_id is null; update users set region_id = 9814731 where id = 102 and region_id is null; update users set region_id = 3470676 where id = 103 and region_id is null; I want to INSERT a delay of 10 seconds every 50 lines. Does pgsql have a waitfor statement like t-sql . Thanks. Does pgsql have a waitfor statement like t-sql. Yes, pg_sleep : pg=> SELECT pg_sleep(10); pg_sleep ---------- (1 row) You could call the pg_sleep function with the PERFORM statement since we don't care about returning values: