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This reverts commit acdca316c3d42299d31c1b47eb792006ffdfc29c.
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Do not attempt to unlock envlock in child process after a fork.
This implements the first two points from https://github.com/rust-lang/rust/issues/64718#issuecomment-793030479
This is a breaking change for cases where the environment is accessed in a Command::pre_exec closure. Except for single-threaded programs these uses were not correct anyway since they aren't async-signal safe.
Note that we had a ui test that explicitly tried `env::set_var` in `pre_exec`. As expected it failed with these changes when I tested locally.
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Fixes to ExitStatus and its docs
* On Unix, properly display every possible wait status (and don't panic on weird values)
* In the documentation, be clear and consistent about "exit status" vs "wait status".
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This is a breaking change for cases where the environment is
accessed in a Command::pre_exec closure. Except for
single-threaded programs these uses were not correct
anyway since they aren't async-signal safe.
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Co-authored-by: David Tolnay <dtolnay@gmail.com>
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This reverts commit 354f19cf2475148994954b6783341620c7445071, reversing
changes made to 0cfba2fd090834c909d5ed9deccdee8170da791b.
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I strongly disagree with tidy in this case but AIUI there is no way to
override it.
Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>
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If different unices have different bit patterns for WIFSTOPPED and
WIFCONTINUED then simply being glibc is probably not good enough for
this rather ad-hoc test to work. Do it on Linux only.
Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>
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MacOS uses a different representation.
Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>
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Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>
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Currently, on Nightly, this panics:
```
use std::process::ExitStatus;
use std::os::unix::process::ExitStatusExt;
fn main() {
let st = ExitStatus::from_raw(0x007f);
println!("st = {}", st);
}
```
This is because the impl of Display assumes that if .code() is None,
.signal() must be Some. That was a false assumption, although it was
true with buggy code before
5b1316f78152a9c066b357ea9addf803d48e114a
unix ExitStatus: Do not treat WIFSTOPPED as WIFSIGNALED
This is not likely to have affected many people in practice, because
`Command` will never produce such a wait status (`ExitStatus`).
Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>
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This is not particularly pretty but the current situation is a mess
and I don't think I'm making it significantly worse.
Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>
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Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>
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Necessary to handle WIFSTOPPED.
Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>
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This is essential for proper reporting of child process status on Unix.
Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>
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Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>
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A unix wait status can contain, at least, exit statuses, termination
signals, and stop signals.
WTERMSIG is only valid if WIFSIGNALED.
https://pubs.opengroup.org/onlinepubs/9699919799/functions/wait.html
It will not be easy to experience this bug with `Command`, because
that doesn't pass WUNTRACED. But you could make an ExitStatus
containing, say, a WIFSTOPPED, from a call to one of the libc wait
functions.
(In the WIFSTOPPED case, there is WSTOPSIG. But a stop signal is
encoded differently to a termination signal, so WTERMSIG and WSTOPSIG
are by no means the same.)
Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>
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If pthread mutex initialization fails, the failure will go unnoticed unless
debug assertions are enabled. Any subsequent use of mutex will also silently
fail, since return values from lock & unlock operations are similarly checked
only through debug assertions.
In some implementations the mutex initialization requires a memory
allocation and so it does fail in practice.
Check that initialization succeeds to ensure that mutex guarantees
mutual exclusion.
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Use posix_spawn() on unix if program is a path
Previously `Command::spawn` would fall back to the non-posix_spawn based
implementation if the `PATH` environment variable was possibly changed.
On systems with a modern (g)libc `posix_spawn()` can be significantly
faster. If program is a path itself the `PATH` environment variable is
not used for the lookup and it should be safe to use the
`posix_spawnp()` method. [1]
We found this, because we have a cli application that effectively runs a
lot of subprocesses. It would sometimes noticeably hang while printing
output. Profiling showed that the process was spending the majority of
time in the kernel's `copy_page_range` function while spawning
subprocesses. During this time the process is completely blocked from
running, explaining why users were reporting the cli app hanging.
Through this we discovered that `std::process::Command` has a fast and
slow path for process execution. The fast path is backed by
`posix_spawnp()` and the slow path by fork/exec syscalls being called
explicitly. Using fork for process creation is supposed to be fast, but
it slows down as your process uses more memory. It's not because the
kernel copies the actual memory from the parent, but it does need to
copy the references to it (see `copy_page_range` above!). We ended up
using the slow path, because the command spawn implementation in falls
back to the slow path if it suspects the PATH environment variable was
changed.
Here is a smallish program demonstrating the slowdown before this code
change:
```
use std::process::Command;
use std::time::Instant;
fn main() {
let mut args = std::env::args().skip(1);
if let Some(size) = args.next() {
// Allocate some memory
let _xs: Vec<_> = std::iter::repeat(0)
.take(size.parse().expect("valid number"))
.collect();
let mut command = Command::new("/bin/sh");
command
.arg("-c")
.arg("echo hello");
if args.next().is_some() {
println!("Overriding PATH");
command.env("PATH", std::env::var("PATH").expect("PATH env var"));
}
let now = Instant::now();
let child = command
.spawn()
.expect("failed to execute process");
println!("Spawn took: {:?}", now.elapsed());
let output = child.wait_with_output().expect("failed to wait on process");
println!("Output: {:?}", output);
} else {
eprintln!("Usage: prog [size]");
std::process::exit(1);
}
()
}
```
Running it and passing different amounts of elements to use to allocate
memory shows that the time taken for `spawn()` can differ quite
significantly. In latter case the `posix_spawnp()` implementation is 30x
faster:
```
$ cargo run --release 10000000
...
Spawn took: 324.275µs
hello
$ cargo run --release 10000000 changepath
...
Overriding PATH
Spawn took: 2.346809ms
hello
$ cargo run --release 100000000
...
Spawn took: 387.842µs
hello
$ cargo run --release 100000000 changepath
...
Overriding PATH
Spawn took: 13.434677ms
hello
```
[1]: https://github.com/bminor/glibc/blob/5f72f9800b250410cad3abfeeb09469ef12b2438/posix/execvpe.c#L81
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The posix_spawnattr_init & posix_spawn_file_actions_init might fail,
but their return code is not checked.
Check for non-zero return code and destroy only succesfully initialized
objects.
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The cvt function compares the argument with -1 and when equal returns a new
io::Error constructed from errno. It is used together posix_spawn_* functions.
This is incorrect. Those functions do not set errno. Instead they return
non-zero error code directly.
Check for non-zero return code and use it to construct a new io::Error.
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This also fixes issues with inconsistent `unsafe` on functions.
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Use posix_spawn on musl targets
The posix_spawn had been available in a form suitable for use in a
Command implementation since musl 0.9.12. Use it in a preference to a
fork when possible, to benefit from CLONE_VM|CLONE_VFORK used there.
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Previously `Command::spawn` would fall back to the non-posix_spawn based
implementation if the `PATH` environment variable was possibly changed.
On systems with a modern (g)libc `posix_spawn()` can be significantly
faster. If program is a path itself the `PATH` environment variable is
not used for the lookup and it should be safe to use the
`posix_spawnp()` method. [1]
We found this, because we have a cli application that effectively runs a
lot of subprocesses. It would sometimes noticeably hang while printing
output. Profiling showed that the process was spending the majority of
time in the kernel's `copy_page_range` function while spawning
subprocesses. During this time the process is completely blocked from
running, explaining why users were reporting the cli app hanging.
Through this we discovered that `std::process::Command` has a fast and
slow path for process execution. The fast path is backed by
`posix_spawnp()` and the slow path by fork/exec syscalls being called
explicitly. Using fork for process creation is supposed to be fast, but
it slows down as your process uses more memory. It's not because the
kernel copies the actual memory from the parent, but it does need to
copy the references to it (see `copy_page_range` above!). We ended up
using the slow path, because the command spawn implementation in falls
back to the slow path if it suspects the PATH environment variable was
changed.
Here is a smallish program demonstrating the slowdown before this code
change:
```
use std::process::Command;
use std::time::Instant;
fn main() {
let mut args = std::env::args().skip(1);
if let Some(size) = args.next() {
// Allocate some memory
let _xs: Vec<_> = std::iter::repeat(0)
.take(size.parse().expect("valid number"))
.collect();
let mut command = Command::new("/bin/sh");
command
.arg("-c")
.arg("echo hello");
if args.next().is_some() {
println!("Overriding PATH");
command.env("PATH", std::env::var("PATH").expect("PATH env var"));
}
let now = Instant::now();
let child = command
.spawn()
.expect("failed to execute process");
println!("Spawn took: {:?}", now.elapsed());
let output = child.wait_with_output().expect("failed to wait on process");
println!("Output: {:?}", output);
} else {
eprintln!("Usage: prog [size]");
std::process::exit(1);
}
()
}
```
Running it and passing different amounts of elements to use to allocate
memory shows that the time taken for `spawn()` can differ quite
significantly. In latter case the `posix_spawnp()` implementation is 30x
faster:
```
$ cargo run --release 10000000
...
Spawn took: 324.275µs
hello
$ cargo run --release 10000000 changepath
...
Overriding PATH
Spawn took: 2.346809ms
hello
$ cargo run --release 100000000
...
Spawn took: 387.842µs
hello
$ cargo run --release 100000000 changepath
...
Overriding PATH
Spawn took: 13.434677ms
hello
```
[1]: https://github.com/bminor/glibc/blob/5f72f9800b250410cad3abfeeb09469ef12b2438/posix/execvpe.c#L81
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Add accessors to Command.
This adds some accessor methods to `Command` to provide a way to access the values set when building the `Command`. An example where this can be useful is to display the command to be executed. This is roughly based on the [`ProcessBuilder`](https://github.com/rust-lang/cargo/blob/13b73cdaf76b2d9182515c9cf26a8f68342d08ef/src/cargo/util/process_builder.rs#L105-L134) in Cargo.
Possible concerns about the API:
- Values with NULs on Unix will be returned as `"<string-with-nul>"`. I don't think it is practical to avoid this, since otherwise a whole separate copy of all the values would need to be kept in `Command`.
- Does not handle `arg0` on Unix. This can be awkward to support in `get_args` and is rarely used. I figure if someone really wants it, it can be added to `CommandExt` as a separate method.
- Does not offer a way to detect `env_clear`. I'm uncertain if it would be useful for anyone.
- Does not offer a way to get an environment variable by name (`get_env`). I figure this can be added later if anyone really wants it. I think the motivation for this is weak, though. Also, the API could be a little awkward (return a `Option<Option<&OsStr>>`?).
- `get_envs` could skip "cleared" entries and just return `&OsStr` values instead of `Option<&OsStr>`. I'm on the fence here. My use case is to display a shell command, and I only intend it to be roughly equivalent to the actual execution, and I probably won't display `None` entries. I erred on the side of providing extra information, but I suspect many situations will just filter out the `None`s.
- Could implement more iterator stuff (like `DoubleEndedIterator`).
I have not implemented new std items before, so I'm uncertain if the existing issue should be reused, or if a new tracking issue is needed.
cc #44434
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The posix_spawn had been available in a form suitable for use in a
Command implementation since musl 0.9.12. Use it in a preference to a
fork when possible, to benefit from CLONE_VM|CLONE_VFORK used there.
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std::sys::unix::process::Command::spawn()
`assert!` panics on failure, which is not signal-safe.
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On Fuchsia, spawning a subprocess does not automatically
clone all of the parent process' capabilities. UTC time on
Fuchsia is managed by a top-level userspace clock capability
that is cloned and passed to subprocesses.
This change ensures that any Rust subprocess gets access to the
UTC clock, if the parent had access to it. This is critical for
tests, which on Fuchsia, use panic=abort and spawn subprocesses
per test.
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This is a work-around for a libc issue:
https://github.com/rust-lang/libc/issues/1888.
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Also doing fmt inplace as requested.
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