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![Jeff King](/assets/img/avatar_default.png)
When you hit ^C to interrupt a git command going to a pager,
this usually leaves the pager running. But when a dashed
external is in use, the pager ends up in a funny state and
quits (but only after eating one more character from the
terminal!). This fixes it.
Explaining the reason will require a little background.
When git runs a pager, it's important for the git process to
hang around and wait for the pager to finish, even though it
has no more data to feed it. This is because git spawns the
pager as a child, and thus the git process is the session
leader on the terminal. After it dies, the pager will finish
its current read from the terminal (eating the one
character), and then get EIO trying to read again.
When you hit ^C, that sends SIGINT to git and to the pager,
and it's a similar situation. The pager ignores it, but the
git process needs to hang around until the pager is done. We
addressed that long ago in a3da882120
(pager: do
wait_for_pager on signal death, 2009-01-22).
But when you have a dashed external (or an alias pointing to
a builtin, which will re-exec git for the builtin), there's
an extra process in the mix. For instance, running:
$ git -c alias.l=log l
will end up with a process tree like:
git (parent)
\
git-log (child)
\
less (pager)
If you hit ^C, SIGINT goes to all of them. The pager ignores
it, and the child git process will end up in wait_for_pager().
But the parent git process will die, and the usual EIO
trouble happens.
So we really want the parent git process to wait_for_pager(),
but of course it doesn't know anything about the pager at
all, since it was started by the child. However, we can
have it wait on the git-log child, which in turn is waiting
on the pager. And that's what this patch does.
There are a few design decisions here worth explaining:
1. The new feature is attached to run-command's
clean_on_exit feature. Partly this is convenience,
since that feature already has a signal handler that
deals with child cleanup.
But it's also a meaningful connection. The main reason
that dashed externals use clean_on_exit is to bind the
two processes together. If somebody kills the parent
with a signal, we propagate that to the child (in this
instance with SIGINT, we do propagate but it doesn't
matter because the original signal went to the whole
process group). Likewise, we do not want the parent
to go away until the child has done so.
In a traditional Unix world, we'd probably accomplish
this binding by just having the parent execve() the
child directly. But since that doesn't work on Windows,
everything goes through run_command's more spawn-like
interface.
2. We do _not_ automatically waitpid() on any
clean_on_exit children. For dashed externals this makes
sense; we know that the parent is doing nothing but
waiting for the child to exit anyway. But with other
children, it's possible that the child, after getting
the signal, could be waiting on the parent to do
something (like closing a descriptor). If we were to
wait on such a child, we'd end up in a deadlock. So
this errs on the side of caution, and lets callers
enable the feature explicitly.
3. When we send children the cleanup signal, we send all
the signals first, before waiting on any children. This
is to avoid the case where one child might be waiting
on another one to exit, causing a deadlock. We inform
all of them that it's time to die before reaping any.
In practice, there is only ever one dashed external run
from a given process, so this doesn't matter much now.
But it future-proofs us if other callers start using
the wait_after_clean mechanism.
There's no automated test here, because it would end up racy
and unportable. But it's easy to reproduce the situation by
running the log command given above and hitting ^C.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
225 lines
7.6 KiB
C
225 lines
7.6 KiB
C
#ifndef RUN_COMMAND_H
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#define RUN_COMMAND_H
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#ifndef NO_PTHREADS
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#include <pthread.h>
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#endif
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#include "argv-array.h"
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struct child_process {
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const char **argv;
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struct argv_array args;
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struct argv_array env_array;
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pid_t pid;
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/*
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* Using .in, .out, .err:
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* - Specify 0 for no redirections (child inherits stdin, stdout,
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* stderr from parent).
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* - Specify -1 to have a pipe allocated as follows:
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* .in: returns the writable pipe end; parent writes to it,
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* the readable pipe end becomes child's stdin
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* .out, .err: returns the readable pipe end; parent reads from
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* it, the writable pipe end becomes child's stdout/stderr
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* The caller of start_command() must close the returned FDs
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* after it has completed reading from/writing to it!
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* - Specify > 0 to set a channel to a particular FD as follows:
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* .in: a readable FD, becomes child's stdin
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* .out: a writable FD, becomes child's stdout/stderr
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* .err: a writable FD, becomes child's stderr
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* The specified FD is closed by start_command(), even in case
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* of errors!
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*/
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int in;
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int out;
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int err;
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const char *dir;
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const char *const *env;
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unsigned no_stdin:1;
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unsigned no_stdout:1;
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unsigned no_stderr:1;
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unsigned git_cmd:1; /* if this is to be git sub-command */
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unsigned silent_exec_failure:1;
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unsigned stdout_to_stderr:1;
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unsigned use_shell:1;
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unsigned clean_on_exit:1;
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unsigned wait_after_clean:1;
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void (*clean_on_exit_handler)(struct child_process *process);
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void *clean_on_exit_handler_cbdata;
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};
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#define CHILD_PROCESS_INIT { NULL, ARGV_ARRAY_INIT, ARGV_ARRAY_INIT }
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void child_process_init(struct child_process *);
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void child_process_clear(struct child_process *);
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int start_command(struct child_process *);
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int finish_command(struct child_process *);
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int finish_command_in_signal(struct child_process *);
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int run_command(struct child_process *);
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/*
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* Returns the path to the hook file, or NULL if the hook is missing
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* or disabled. Note that this points to static storage that will be
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* overwritten by further calls to find_hook and run_hook_*.
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*/
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extern const char *find_hook(const char *name);
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LAST_ARG_MUST_BE_NULL
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extern int run_hook_le(const char *const *env, const char *name, ...);
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extern int run_hook_ve(const char *const *env, const char *name, va_list args);
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#define RUN_COMMAND_NO_STDIN 1
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#define RUN_GIT_CMD 2 /*If this is to be git sub-command */
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#define RUN_COMMAND_STDOUT_TO_STDERR 4
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#define RUN_SILENT_EXEC_FAILURE 8
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#define RUN_USING_SHELL 16
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#define RUN_CLEAN_ON_EXIT 32
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int run_command_v_opt(const char **argv, int opt);
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/*
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* env (the environment) is to be formatted like environ: "VAR=VALUE".
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* To unset an environment variable use just "VAR".
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*/
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int run_command_v_opt_cd_env(const char **argv, int opt, const char *dir, const char *const *env);
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/**
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* Execute the given command, sending "in" to its stdin, and capturing its
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* stdout and stderr in the "out" and "err" strbufs. Any of the three may
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* be NULL to skip processing.
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*
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* Returns -1 if starting the command fails or reading fails, and otherwise
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* returns the exit code of the command. Any output collected in the
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* buffers is kept even if the command returns a non-zero exit. The hint fields
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* gives starting sizes for the strbuf allocations.
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*
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* The fields of "cmd" should be set up as they would for a normal run_command
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* invocation. But note that there is no need to set the in, out, or err
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* fields; pipe_command handles that automatically.
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*/
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int pipe_command(struct child_process *cmd,
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const char *in, size_t in_len,
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struct strbuf *out, size_t out_hint,
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struct strbuf *err, size_t err_hint);
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/**
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* Convenience wrapper around pipe_command for the common case
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* of capturing only stdout.
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*/
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static inline int capture_command(struct child_process *cmd,
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struct strbuf *out,
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size_t hint)
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{
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return pipe_command(cmd, NULL, 0, out, hint, NULL, 0);
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}
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/*
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* The purpose of the following functions is to feed a pipe by running
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* a function asynchronously and providing output that the caller reads.
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*
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* It is expected that no synchronization and mutual exclusion between
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* the caller and the feed function is necessary so that the function
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* can run in a thread without interfering with the caller.
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*/
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struct async {
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/*
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* proc reads from in; closes it before return
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* proc writes to out; closes it before return
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* returns 0 on success, non-zero on failure
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*/
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int (*proc)(int in, int out, void *data);
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void *data;
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int in; /* caller writes here and closes it */
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int out; /* caller reads from here and closes it */
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#ifdef NO_PTHREADS
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pid_t pid;
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#else
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pthread_t tid;
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int proc_in;
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int proc_out;
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#endif
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int isolate_sigpipe;
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};
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int start_async(struct async *async);
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int finish_async(struct async *async);
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int in_async(void);
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void check_pipe(int err);
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/**
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* This callback should initialize the child process and preload the
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* error channel if desired. The preloading of is useful if you want to
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* have a message printed directly before the output of the child process.
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* pp_cb is the callback cookie as passed to run_processes_parallel.
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* You can store a child process specific callback cookie in pp_task_cb.
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*
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* Even after returning 0 to indicate that there are no more processes,
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* this function will be called again until there are no more running
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* child processes.
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*
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* Return 1 if the next child is ready to run.
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* Return 0 if there are currently no more tasks to be processed.
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* To send a signal to other child processes for abortion,
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* return the negative signal number.
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*/
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typedef int (*get_next_task_fn)(struct child_process *cp,
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struct strbuf *out,
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void *pp_cb,
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void **pp_task_cb);
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/**
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* This callback is called whenever there are problems starting
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* a new process.
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*
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* You must not write to stdout or stderr in this function. Add your
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* message to the strbuf out instead, which will be printed without
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* messing up the output of the other parallel processes.
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*
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* pp_cb is the callback cookie as passed into run_processes_parallel,
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* pp_task_cb is the callback cookie as passed into get_next_task_fn.
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*
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* Return 0 to continue the parallel processing. To abort return non zero.
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* To send a signal to other child processes for abortion, return
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* the negative signal number.
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*/
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typedef int (*start_failure_fn)(struct strbuf *out,
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void *pp_cb,
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void *pp_task_cb);
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/**
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* This callback is called on every child process that finished processing.
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*
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* You must not write to stdout or stderr in this function. Add your
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* message to the strbuf out instead, which will be printed without
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* messing up the output of the other parallel processes.
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*
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* pp_cb is the callback cookie as passed into run_processes_parallel,
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* pp_task_cb is the callback cookie as passed into get_next_task_fn.
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*
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* Return 0 to continue the parallel processing. To abort return non zero.
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* To send a signal to other child processes for abortion, return
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* the negative signal number.
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*/
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typedef int (*task_finished_fn)(int result,
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struct strbuf *out,
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void *pp_cb,
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void *pp_task_cb);
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/**
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* Runs up to n processes at the same time. Whenever a process can be
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* started, the callback get_next_task_fn is called to obtain the data
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* required to start another child process.
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*
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* The children started via this function run in parallel. Their output
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* (both stdout and stderr) is routed to stderr in a manner that output
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* from different tasks does not interleave.
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*
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* start_failure_fn and task_finished_fn can be NULL to omit any
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* special handling.
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*/
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int run_processes_parallel(int n,
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get_next_task_fn,
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start_failure_fn,
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task_finished_fn,
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void *pp_cb);
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#endif
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