waitpid == -1 and errno == ECHILD
in [Unix Programming]
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From: alexandrug on 28 Nov 2009 08:16 On Nov 28, 12:59 am, pac...(a)kosh.dhis.org (Alan Curry) wrote: > In article <e22036c1-e514-430d-b372-93681ff25...(a)m3g2000yqf.googlegroups.com>, > > > > alexandrug <webaig...(a)gmail.com> wrote: > >> > In what conditions we can have waitpid == -1 and errno == ECHILD, > >> > supposing that the signal handler for SIGCHLD is NOT SIG_IGN ? > > >More precisely, the code is like this : > > >{ > >pid = fork(); > >int exitcode = 0; > > >if (pid == 0) while(1) { do_some_actions(); } > > >// only in parent process > > >if ( waitpid(pid, &exitcode,0) == -1) > >{ > >switch(errno) { > >case ECHILD: do_something(); > > break; > >case EINTR: break; > >default : break; > > >} > >} > > It could happen if pid==(pid_t)-1 i.e. fork failed, which you didn't check > for. > > -- > Alan Curry Suppose that 1) pid = fork() > 0, in parent process (ie, fork() was successful) 2) there is NOT any handler for SIGCHLD, that colls wait*() 3) there is NOT any thread which calls wait*() 4) the signal handler for SIGCHLD is set, but NOT to SIG_IGN 5) at runtime, we have waitpid(pid, &exitcode, 0) == -1 In what conditions we could have errno == ECHILD ? (*) I noticed that if I kill -9 (manually) the child process, then the child process (defunct) will still exist in the process table, and a waitpid() on it would return a code of success. Please help me with my question : (*). Thanks, Alexandru.
From: Alan Curry on 28 Nov 2009 17:29
In article <31306251-f3bb-49e4-8a2d-624f72af585c(a)9g2000yqa.googlegroups.com>, alexandrug <webaigoia(a)gmail.com> wrote: >On Nov 28, 12:59�am, pac...(a)kosh.dhis.org (Alan Curry) wrote: > >Suppose that > >1) pid = fork() > 0, in parent process (ie, fork() was successful) >2) there is NOT any handler for SIGCHLD, that colls wait*() >3) there is NOT any thread which calls wait*() >4) the signal handler for SIGCHLD is set, but NOT to SIG_IGN > >5) at runtime, we have waitpid(pid, &exitcode, 0) == -1 > >In what conditions we could have errno == ECHILD ? (*) Let's just say it's a kernel bug. If it's reproducable, write a minimal test program that demonstrates it, put a system("ps axj") after the errno==ECHILD test, and follow your vendor's bug reporting procedure. -- Alan Curry |