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Wait on individual processes in a job in reverse order

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This fixes #5438 by having fish block while waiting on a foreground job
via its individual processes by enumerating the procs in reverse order,
such that we hang waiting for the last job in the IO chain to terminate,
rather than the first.
This commit is contained in:
Mahmoud Al-Qudsi 2018-12-30 19:02:38 -06:00
parent b0072482e4
commit 259cf02aac
1 changed files with 13 additions and 3 deletions
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16
src/proc.cpp
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@ -451,7 +451,12 @@ static bool process_mark_finished_children(bool block_on_fg) {
// If the pgid is 0, we need to wait by process because that's invalid.
// This happens in firejail for reasons not entirely clear to me.
bool wait_by_process = !j->job_chain_is_fully_constructed() || j->pgid == 0;
process_list_t::iterator process = j->processes.begin();
// When waiting on processes individually in a pipeline, we need to enumerate in reverse
// order so that the first process we actually wait on (i.e. ~WNOHANG) is the last process
// in the IO chain, because that's the one that controls the lifetime of the foreground job
// - as long as it is still running, we are in the background and once it exits or is
// killed, all previous jobs in the IO pipeline must necessarily terminate as well.
auto process = j->processes.rbegin();
// waitpid(2) returns 1 process each time, we need to keep calling it until we've reaped all
// children of the pgrp in question or else we can't reset the dirty_state flag. In all
// cases, calling waitpid(2) is faster than potentially calling select_try() on a process
@ -469,10 +474,15 @@ static bool process_mark_finished_children(bool block_on_fg) {
// parent job has been fully constructed), we need to call waitpid(2) on the
// individual processes of the child job instead of using a catch-all waitpid(2)
// call on the job's process group.
if (process == j->processes.end()) {
if (process == j->processes.rend()) {
break;
}
assert((*process)->pid != INVALID_PID && "Waiting by process on an invalid PID!");
if ((options & WNOHANG) == 0) {
debug(4, "Waiting on individual process %d", (*process)->pid);
} else {
debug(4, "waitpid with WNOHANG on individual process %d", (*process)->pid);
}
pid = waitpid((*process)->pid, &status, options);
process++;
} else {
@ -513,7 +523,7 @@ static bool process_mark_finished_children(bool block_on_fg) {
}
// Poll disowned processes/process groups, but do nothing with the result. Only used to avoid
// zombie processes. Entries have already be converted to negative for process groups.
// zombie processes. Entries have already been converted to negative for process groups.
int status;
s_disowned_pids.erase(std::remove_if(s_disowned_pids.begin(), s_disowned_pids.end(),
[&status](pid_t pid) { return waitpid(pid, &status, WNOHANG) > 0; }),