1
2

To allow other threads to continue execution, 
the main thread should terminate by calling pthread_exit() rather than exit(3).

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36

 http://man7.org/linux/man-pages/man3/pthread_exit.3.html 
NAME  
       void pthread_exit(void *retval);
DESCRIPTION        
    
       The pthread_exit() function terminates the calling thread and returns
       a value via retval that (if the thread is joinable) is available to
       another thread in the same process that calls pthread_join(3).

       Any clean-up handlers established by pthread_cleanup_push(3) that
       have not yet been popped, are popped (in the reverse of the order in
       which they were pushed) and executed.  If the thread has any thread-
       specific data, then, after the clean-up handlers have been executed,
       the corresponding destructor functions are called, in an unspecified
       order.

       When a thread terminates, process-shared resources (e.g., mutexes,
       condition variables, semaphores, and file descriptors) are not
       released, and functions registered using atexit(3) are not called.

       After the last thread in a process terminates, the process terminates
       as by calling exit(3) with an exit status of zero; thus, process-
       shared resources are releas
  NOTES       
           
       Performing a return from the start function of any thread other than
       the main thread results in an implicit call to pthread_exit(), using
       the function's return value as the thread's exit status.

       To allow other threads to continue execution, the main thread should
       terminate by calling pthread_exit() rather than exit(3).

       The value pointed to by retval should not be located on the calling
       thread's stack, since the contents of that stack are undefined after
       the thread terminates.
           

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46

exit - cause normal process termination

 The exit() function causes normal process termination and the value
       of status & 0377 is returned to the parent (see wait(2)).
  看进程的销毁图片         
  All functions registered with atexit(3) and on_exit(3) are called, in
       the reverse order of their registration.

  
  NOTE
 进程销毁 上下都要打点
 
   After exit(), the exit status must be transmitted to the parent
       process.  There are three cases:

       ·  If the parent has set SA_NOCLDWAIT, or has set the SIGCHLD handler
          to SIG_IGN, the status is discarded and the child dies
          immediately.

       ·  If the parent was waiting on the child, it is notified of the exit
          status and the child dies immediately.

       ·  Otherwise, the child becomes a "zombie" process: most of the
          process resources are recycled, but a slot containing minimal
          information about the child process (termination status, resource
          usage statistics) is retained in process table.  This allows the
          parent to subsequently use waitpid(2) (or similar) to learn the
          termination status of the child; at that point the zombie process
          slot is released.

       If the implementation supports the SIGCHLD signal, this signal is
       sent to the parent.  If the parent has set SA_NOCLDWAIT, it is
       undefined whether a SIGCHLD signal is sent.

   Signals sent to other processes
       If the exiting process is a session leader and its controlling
       terminal is the controlling terminal of the session, then each
       process in the foreground process group of this controlling terminal
       is sent a SIGHUP signal, and the terminal is disassociated from this
       session, allowing it to be acquired by a new controlling process.

       If the exit of the process causes a process group to become orphaned,
       and if any member of the newly orphaned process group is stopped,
       then a SIGHUP signal followed by a SIGCONT signal will be sent to
       each process in this process group.  See setpgid(2) for an
       explanation of orphaned process groups.

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17

strace ./a.out
execve("./a.out", ["./a.out"], [/* 30 vars */]) = 0
brk(NULL)                               = 0xd9e000
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f52dcaaa000
    
The  exec()  family of functions replaces the current process image with a new process image
    
    
strace ls
execve("/bin/ls", ["ls"], [/* 29 vars */]) = 0
brk(NULL)                               = 0x19aa000
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fc7e7ad6000
access("/etc/ld.so.preload", R_OK)      = -1 ENOENT (No such file or directory)
open("tls/x86_64/libselinux.so.1", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
open("tls/libselinux.so.1", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
open("x86_64/libselinux.so.1", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
open("libselinux.so.1", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)    

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20

TCP:
#ifdef WIN32
	SOCKET ss = ::socket(PF_INET, SOCK_STREAM, 0);
#else
	SOCKET ss = ::socket(PF_INET, SOCK_STREAM | SOCK_CLOEXEC, 0);
#endif

文件：
int fd = open(“foo.txt”,O_RDONLY);
int flags = fcntl(fd, F_GETFD);
flags |= FD_CLOEXEC;
fcntl(fd, F_SETFD, flags);

int fd = open(“foo.txt”,O_RDONLY | O_CLOEXEC);


 O_CLOEXEC (since Linux 2.6.23)
              Enable the close-on-exec flag for the new file descriptor.
              Specifying this flag permits a program to avoid additional
              fcntl(2) F_SETFD operations to set the FD_CLOEXEC flag.