C++11 provides std::min/std::max which we're using all over,
obviating the need for our own templates for this.
util.h now only provides two things: get_time and wcsfilecmp.
This commit removes everything that includes it which doesn't
use either; most because they no longer need mini or maxi from
it but some others were #including it unnecessarily.
Prior to this fix, the wait command used waitpid() directly. Switch it to
calling process_mark_finished_children() along with the rest of the job
machinery. This centralizes the waitpid call to a single location.
In fish we play fast and loose with status codes as set directly (e.g. on
failed redirections), vs status codes returned from waitpid(), versus the
value $status. Introduce a new value type proc_status_t to encapsulate
this logic.
Prior to this fix, an "event" was used as both a predicate on which events
to match, and also as the event itself. Re-express these concepts
distinctly: an event is something that happened, an event_handler is the
predicate and name of the function to execute.
Prior to this fix, fish had a signal_list_t that accumulated signals.
Signals were added to an array of integers, with an overflow flag.
The event machinery would attempt to atomically "swap in" the other list.
After this fix, there is a single list of pending signal events, as an array
of atomic booleans. The signal handler sets the boolean corresponding to its
signal.
This uses the new internal process mechanism to write output for builtins.
After this the only reason fish ever forks is to execute external processes.
This introduces "internal processes" which are backed by a pthread instead
of a normal process. Internal processes are reaped using the topic
machinery, plugging in neatly alongside the sigchld topic; this means that
process_mark_finished_children() can wait for internal and external
processes simultaneously.
Initially internal processes replace the forked process that fish uses to
write out the output of blocks and functions.
The sigchld generation expresses the idea that, if we receive a sigchld
signal, the generation will be different than when we last recorded it. A
process cannot exit before it has launched, so check the generation count
before process launch. This is an optimization that reduces failing
waitpid calls.
This is a big change to how process reaping works, reimplenting it using
topics. The idea is to simplify the logic in
process_mark_finished_children around blocking, and also prepare for
"internal processes" which do not correspond to real processes.
Before this change, fish would use waitpid() to wait for a process group,
OR would individually poll processes if the process group leader was
unreapable.
After this change, fish no longer ever calls blocking waitpid(). Instead
fish uses the topic mechanism. For each reapable process, fish checks if
it has received a SIGCHLD since last poll; if not it waits until the next
SIGCHLD, and then polls them all.
This is a large change to how io_buffers are filled. The essential problem
comes about with code like (example):
echo ( /bin/pwd )
The output of /bin/pwd must go to fish, not the tty. To arrange for this,
fish does the following:
1. Invoke pipe() to create a pipe.
2. Add an io_bufferfill_t redirection that owns the write end of the pipe.
3. After fork (or equiv), call dup2() to replace pwd's stdout with this pipe.
Now when /bin/pwd writes, it will send output to the read end of the pipe.
But who reads it?
Prior to this fix, fish would do the following in a loop:
1. select() on the pipe with a 10 msec timeout
2. waitpid(WNOHANG) on the pwd proc
This polling is ugly and confusing and is what is replaced here.
With this new change, fish now reads from the pipe via a background thread:
1. Spawn a background pthread, which select()s on the pipe's read end with
a long (100 msec) timeout.
2. In the foreground, waitpid() (allowing hanging) on the pwd proc.
The big win here is a major simplification of job_t::continue_job() since
it no longer has to worry about filling buffers. This will make things
easier for concurrent execution.
It may not be obvious why the background thread still needs a poll (100 msec).
The answer is for cases where the write end of the fd escapes, in particular
background processes invoked inside command substitutions. psub is perhaps
the only important case of this (other shells typically just hang here).
This makes some significant architectual improvements to io_pipe_t and
io_buffer_t.
Prior to this fix, io_buffer_t subclassed io_pipe_t. io_buffer_t is now
replaced with a class io_bufferfill_t, which does not subclass pipe.
io_pipe_t no longer remembers both fds. Instead it has an autoclose_fd_t,
so that the file descriptor ownership is clear.
This is a large change to how io_buffers are filled. The essential problem
comes about with code like (example):
echo ( /bin/pwd )
The output of /bin/pwd must go to fish, not the tty. To arrange for this,
fish does the following:
1. Invoke pipe() to create a pipe.
2. Add an io_bufferfill_t redirection that owns the write end of the pipe.
3. After fork (or equiv), call dup2() to replace pwd's stdout with this pipe.
Now when /bin/pwd writes, it will send output to the read end of the pipe.
But who reads it?
Prior to this fix, fish would do the following in a loop:
1. select() on the pipe with a 10 msec timeout
2. waitpid(WNOHANG) on the pwd proc
This polling is ugly and confusing and is what is replaced here.
With this new change, fish now reads from the pipe via a background thread:
1. Spawn a background pthread, which select()s on the pipe's read end with
a long (100 msec) timeout.
2. In the foreground, waitpid() (allowing hanging) on the pwd proc.
The big win here is a major simplification of job_t::continue_job() since
it no longer has to worry about filling buffers. This will make things
easier for concurrent execution.
It may not be obvious why the background thread still needs a poll (100 msec).
The answer is for cases where the write end of the fd escapes, in particular
background processes invoked inside command substitutions. psub is perhaps
the only important case of this (other shells typically just hang here).
This makes some significant architectual improvements to io_pipe_t and
io_buffer_t.
Prior to this fix, io_buffer_t subclassed io_pipe_t. io_buffer_t is now
replaced with a class io_bufferfill_t, which does not subclass pipe.
io_pipe_t no longer remembers both fds. Instead it has an autoclose_fd_t,
so that the file descriptor ownership is clear.
By exclusively waiting by pgrp, we can fail to reap processes that
change their own pgrp then either crash or close their fds. If we wind
up in a situation where `waitpid(2)` returns 0 or ECHLD even though we
did not specify `WNOHANG` but we still have unreaped child processes,
wait on them by pid.
Closes#5596.
This is effectively a pick of 2ebdcf82ee
and the subsequent fixup. However we also avoid setting WNOHANG unless
waitpid() indicates a process was reaped.
Fixes#5438
This is the more correct fix for #5447, as regardless of which process
in the job (be it the first or the last) finished first, once we have
waited on a process without ~WNOHANG we don't do that for any subsequent
processes in the job.
It is also a waste to call into the kernel to wait for a process we
already know is completed!
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.
The function `add_disowned_pgid` adds process *group* ids and not
process ids. It multiplies the value by negative 1 to indicate a wait
on a process group, so the original value must be positive.
If a job is disowned that, for some reason, has a pgid that is special
to waitpid, like 0 (process with pgid of the calling process), -1 (any
process), or our actual pgid, that would lead to us waiting for too
many processes when we later try to reap the disowned processes (to
stop zombies from appearing).
And that means we'd snag away the processes we actually do want to
wait for, which would end with us in a waiting loop.
This is tough to reproduce, the easiest I've found was
fish -ic 'sleep 5 &; disown; set -g __fish_git_prompt_showupstream auto; __fish_git_prompt'
in a git repo.
What we do is to not allow special pgids in the disowned_pids list.
That means we might leave a zombie around (though we probably wait on
0 somewhere), but that's preferable to infinitely looping.
See #5426.
This happens in firejail, and it means that we can't use it as an
argument to most pgid-taking functions.
E.g. `wait(0)` means to wait for the _current_ process group,
`tcsetpgrp(0)` doesn't work etc.
So we just stop doing this stuff and hope it works.
Fixes#5295.
This reverts commit 1cb8b2a87b.
argv[0] has the full path in it for a user when he executes it
out of $PATH. This is really annoying in the title which uses $_.
