This concerns builtins writing to an io_buffer_t. io_buffer_t is how fish
captures output, especially in command substitutions:
set STUFF (string upper stuff)
Recall that io_buffer_t fills itself by reading from an fd (typically
connected to stdout of the command). However if our command is a builtin,
then we can write to the buffer directly.
Prior to this change, when a builtin anticipated writing to an
io_buffer_t, it would first write into an internal buffer, and then after
the builtin was finished, we would copy it to the io_buffer_t. This was
because we didn't have a polymorphic receiver for builtin output: we
always buffered it and then directed it to the io_buffer_t or file
descriptor or stdout or whatever.
Now that we have polymorphpic io_streams_t, we can notice ahead of time
that the builtin output is destined for an internal buffer and have it
just write directly to that buffer. This saves a buffering step, which is
a nice simplification.
This removes the 100 msec timeout from io_buffer_t. We no longer need to
periodically wake up to check if a command substitution is finished,
because we get explicitly poked when that happens.
io_buffer_t is used to buffer output from a command substitution, so we
can split it into arguments. Typically io_buffer_t reads from its pipe
until it gets EOF and then stops reading. However it may be that the
cmdsub ends but EOF is not delivered because the stdout of the cmdsub
escaped with a background process.
Prior to this change we would wake up every 100 msec (select timeout) to
check if the cmdsub is finished. However this 100 msec adds latency if a
background process is launched from e.g. fish_prompt.
Switch to the new poke() function. Now when the cmdsub is finished, it
pokes its item, which explicitly wakes it up. This removes the extra
latency.
Fixes#7559
In preparation for fixing #7559, add a function poke_item to fd_monitor.
fd_monitor has a list of file descriptors, and invokes a callback when an
fd becomes readable. With this change, we assign each item a unique ID and
return it when the item is added; the ID may then be used to invoke the
callback explicitly.
The idea is that we can stop reading from the pipe associated with the
cmdsub when the job is finished, even if the pipe is still open.
It was possible though unlikely for make_autoclose_pipes to close only
one side of pipe, if it fails to find a new fd. This would result in an
fd leak. Ensure that doesn't happen.
builtins output to stdout and stderr via io_streams_t. Prior to this fix, it
contained an output_stream_t which just wraps a buffer. So all builtin output
went to this buffer (except for eval).
Switch output_stream_t to become a new abstract class which can output to a
buffer, file descriptor, or nowhere. This allows for example `string` to stream
its output as it is produced, instead of buffering it.
Currently fish aborts execution mid-pipeline if a file redirection
failed, which can leave the shell in a broken state (job abandoned after
giving control of the terminal to an already-executed job in the
pipeline).
This patch replaces a failed fd with a closed fd and continues execution
if the affected process wasn't the first in the pipeline.
While this is a hack to address the regression behind fish-shell/#7038
introduced in d62576c, it can also be argued that this behavior is
actually more correct... right?
Closes#7038.
Prior to this fix, builtin_eval would direct output to the io_chain of the
job. The problem is with pipes: `builtin_eval` might happily attempt to
write unlimited output to the write end of a pipe, but the corresponding
reading process has not yet been launched. This results in deadlock.
The fix is to buffer all the output from `builtin_eval`. This is not fun
but the best that can be done until we have real concurrent processes.
Fixes#6806
This switches bufferfills from using an exclusively-owned thread, to
sharing an fd_monitor. This allows multiple bufferfills to all use the same
thread.
Sometimes we must spawn a new thread, to avoid the risk of deadlock.
Ensure we always spawn a thread in those cases. In particular this
includes the fillthread.
user_supplied was used to distinguish IO redirections which were
explicit, vs those that came about through "transmogrphication." But
transmogrification is no more. Remove the flag.
The IO cleanup left file redirections open in the child. For example,
/bin/cmd < file.txt would redirect stdin but also leave the file open.
Ensure these get closed properly.
Prior to this fix, a file redirection was turned into an io_file_t. This is
annoying because every place where we want to apply the redirection, we
might fail due to open() failing. Switch to opening the file at the point
we resolve the redirection spec. This will simplify a lot of code.
Prior to this change, a process after it has been constructed by
parse_execution, but before it is executed, was given a list of
io_data_t redirections. The problem is that redirections have a
sensitive ownership policy because they hold onto fds. This made it
rather hard to reason about fd lifetime.
Change these to redirection_spec_t. This is a textual description
of a redirection after expansion. It does not represent an open file and
so its lifetime is no longer important.
This enables files to be held only on the stack, and are no longer owned
by a process of indeterminate lifetime.
fish has to ensure that the pipes it creates do not conflict with any
explicit fds named in redirections. Switch this code to using
autoclose_fd_t to make the ownership logic more explicit, and also
introduce fd_set_t to reduce the dependence on io_chain_t.
Background fillthreads are used when we want to populate a buffer from an
external command. The most common is command substitution.
Prior to this commit, fish would spin up a fillthread whenever required.
This ended up being quite expensive.
Switch to using the iothread pool instead. This enables reusing the same
thread(s), which prevents needing to spawn new threads. This shows a big
perf win on the alias benchmark (766 -> 378 ms).
Previously when propagating explicitly separated output, we would early-out
if the buffer was empty, where empty meant contains no characters. However
it may contain one or more empty strings, in which case we should propagate
those strings.
Remove this footgun "empty" function and handle this properly.
Fixes#5987
This runs build_tools/style.fish, which runs clang-format on C++, fish_indent on fish and (new) black on python.
If anything is wrong with the formatting, we should fix the tools, but automated formatting is worth it.
