perl多任务问题

use POSIX ':sys_wait_h';    # for &WNOHANG

# how to create a new background process
$pid = fork();
if (!defined $pid) { die "fork() failed!" }
if ($pid == 0) { # child
    # ... do stuff in background ...
    exit 0;      # don't forget to exit or die from the child process
} 
# else this is the parent,$pid contains process id of child process
# ... do stuff in foreground ...

# how to tell if a process is finished
# also see  perldoc perlipc
$pid = waitpid -1,0;           # blocking wait for any process
$pid = wait;                    # blocking wait for any process
$pid = waitpid $mypid,0;       # blocking wait for process $mypid
# after blocking wait/waitpid
if ($pid == -1) {
    print "All child processes are finished.n";
} else {
    print "Process $pid is finished.n";
    print "The exit status of process $pid was $?n";
}

$pid = waitpid -1,&WNOHANG;    # non-blocking wait for any process
$pid = waitpid $mypid,0;       # blocking wait for process $mypid
if ($pid == -1) {
    print "No child processes have finished since last wait/waitpid call.n";
} else {
    print "Process $pid is finished.n";
    print "The exit status of process $pid was $?n";
}

# terminating a process - see  perldoc -f kill  or  perldoc perlipc
# this can be flaky on Windows
kill 'INT',$pid;               # send SIGINT to process $pid

在perldoc -f fork,waitpid,wait,kill和perlipc中的Gory细节.关于为SIGCHLD事件设置处理程序的perlipc中的内容应该特别有用,尽管在Windows上不支持.

分叉进程的I / O在Unix和Windows上通常是安全的.文件描述符是共享的,所以对于这样的事情

open X,">",$file;
if (fork() == 0) {  # in child
    print X "Childn"; 
    close X;
    exit 0;
}
# in parent
sleep 1;
print X "Parentn";
close X;

子进程和父进程都会成功写入同一个文件(但要注意输出缓冲).