Rather than forcing my program to the foreground, my program wants to know whether it was executed in the background with &, or whether it is in the foreground.
I am testing tcgetpgrp(fileno(stdin) against getpgid(getpid()). If they are different, my program avoids calling tcgetattr() and tcsetattr(), thus avoiding an unnecessary SIGTTOU if terminal I/O is not needed. Is there a better way to determine if a program is running in the background? Also, it looks like SUSv3 posix_spawn() can set the process group: If the POSIX_SPAWN_SETPGROUP flag is set in the spawn-flags attribute of the object referenced by attrp, and the spawn-pgroup attribute of the same object is non-zero, then the child's process group shall be as specified in the spawn-pgroup attribute of the object referenced by attrp. As a special case, if the POSIX_SPAWN_SETPGROUP flag is set in the spawn-flags attribute of the object referenced by attrp, and the spawn-pgroup attribute of the same object is set to zero, then the child shall be in a new process group with a process group ID equal to its process ID. If the POSIX_SPAWN_SETPGROUP flag is not set in the spawn-flags attribute of the object referenced by attrp, the new child process shall inherit the parent's process group. Thanks, Brian Ginn -----Original Message----- From: ast-developers-boun...@research.att.com [mailto:ast-developers-boun...@research.att.com] On Behalf Of David Korn Sent: Tuesday, June 14, 2011 1:32 PM To: ast-developers@research.att.com; Brian Ginn Subject: Re: [ast-developers] ksh process group problem cc: ast-developers@research.att.com Subject: Re: [ast-developers] ksh process group problem -------- ksh93 uses posix_spawn() rather than fork/exec to run a simple command for performance reasons. However, posix_spawnv() doesn't have a way to set the terminal group before the exec(). The parent process sets the terminal group which leads to the race. There is a simple change you can make to a program to guarentee that the terminal will get set at the beginning of the program. You can add two lines. One line is #include <termios.h> and for the other line tcsetpgrp(2,getpgrp()); Alternatively, you can write a program that does these two lines and then execs the original program. > I am seeing an intermittent problem on Red Hat Enterprise Linux 5.4 and 5.6, > and > HP-UX 11.0 and 11.31. > The processes launched from the AST ksh sometimes "own" the terminal, and > someti > mes don't. > > > Output from the test program below demonstrates the issue: > > > [fbg@sturgeon ~]$ /opt/ast/bin/ksh > > $ /tmp/testprocessgroup_linux64 > > PID: 8678 MY_pgrp=8678 STDIN_PGRP:8674 --DO NOT own terminal > > $ /tmp/testprocessgroup_linux64 > > PID: 8679 MY_pgrp=8679 STDIN_PGRP:8679 --own terminal > > $ /tmp/testprocessgroup_linux64 > > PID: 8680 MY_pgrp=8680 STDIN_PGRP:8680 --own terminal > > $ /tmp/testprocessgroup_linux64 > > PID: 8681 MY_pgrp=8681 STDIN_PGRP:8681 --own terminal > > $ /tmp/testprocessgroup_linux64 > > PID: 8682 MY_pgrp=8682 STDIN_PGRP:8674 --DO NOT own terminal > > $ /tmp/testprocessgroup_linux64 > > PID: 8683 MY_pgrp=8683 STDIN_PGRP:8683 --own terminal > > $ /tmp/testprocessgroup_linux64 > > PID: 8684 MY_pgrp=8684 STDIN_PGRP:8674 --DO NOT own terminal > > $ > > > > > [fbg@sturgeon pgrp]$ cat testprocessgroup.c > #include <stdio.h> > #include <sys/types.h> > #include <unistd.h> > #include <sys/stat.h> > #include <fcntl.h> > > int main(int argc, char **argv) > { > int devtty; > > > printf("PID:%5lu MY_pgrp=%d STDIN_PGRP:%d --%s\n", > getpid(), > getpgid(getpid()), > tcgetpgrp(fileno(stdin)), > tcgetpgrp(fileno(stdin)) == getpgid(getpid()) ? "own terminal" > : > "DO NOT own terminal" ); > > > return(0); > } > > ______________________________________________________________________ > This email has been scanned by the MessageLabs Email Security System. > For more information please visit http://www.messagelabs.com/email > ______________________________________________________________________ > (attachment 1 171/10586 text/html "1.att") > > _______________________________________________ > ast-developers mailing list > ast-developers@research.att.com > https://mailman.research.att.com/mailman/listinfo/ast-developers > David Korn d...@research.att.com _______________________________________________ ast-developers mailing list ast-developers@research.att.com https://mailman.research.att.com/mailman/listinfo/ast-developers ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please visit http://www.messagelabs.com/email ______________________________________________________________________ _______________________________________________ ast-developers mailing list ast-developers@research.att.com https://mailman.research.att.com/mailman/listinfo/ast-developers
