library/std/src/sys/unix/process/process_unix.rs - third_party/rust - Git at Google

 use crate::convert::TryInto;
 use crate::fmt;
 use crate::io::{self, Error, ErrorKind};
 use crate::ptr;
 use crate::sys;
 use crate::sys::cvt;
 use crate::sys::process::process_common::*;

 #[cfg(target_os = "vxworks")]
 use libc::RTP_ID as pid_t;

 #[cfg(not(target_os = "vxworks"))]
 use libc::{c_int, gid_t, pid_t, uid_t};

 ////////////////////////////////////////////////////////////////////////////////
 // Command
 ////////////////////////////////////////////////////////////////////////////////

 impl Command {
     pub fn spawn(
         &mut self,
         default: Stdio,
         needs_stdin: bool,
     ) -> io::Result<(Process, StdioPipes)> {
         const CLOEXEC_MSG_FOOTER: [u8; 4] = *b"NOEX";

         let envp = self.capture_env();

         if self.saw_nul() {
             return Err(io::Error::new(ErrorKind::InvalidInput, "nul byte found in provided data"));
         }

         let (ours, theirs) = self.setup_io(default, needs_stdin)?;

         if let Some(ret) = self.posix_spawn(&theirs, envp.as_ref())? {
             return Ok((ret, ours));
         }

         let (input, output) = sys::pipe::anon_pipe()?;

         // Whatever happens after the fork is almost for sure going to touch or
         // look at the environment in one way or another (PATH in `execvp` or
         // accessing the `environ` pointer ourselves). Make sure no other thread
         // is accessing the environment when we do the fork itself.
         //
         // Note that as soon as we're done with the fork there's no need to hold
         // a lock any more because the parent won't do anything and the child is
         // in its own process.
         let result = unsafe {
             let _env_lock = sys::os::env_lock();
             cvt(libc::fork())?
         };

         let pid = unsafe {
             match result {
                 0 => {
                     drop(input);
                     let Err(err) = self.do_exec(theirs, envp.as_ref());
                     let errno = err.raw_os_error().unwrap_or(libc::EINVAL) as u32;
                     let errno = errno.to_be_bytes();
                     let bytes = [
                         errno[0],
                         errno[1],
                         errno[2],
                         errno[3],
                         CLOEXEC_MSG_FOOTER[0],
                         CLOEXEC_MSG_FOOTER[1],
                         CLOEXEC_MSG_FOOTER[2],
                         CLOEXEC_MSG_FOOTER[3],
                     ];
                     // pipe I/O up to PIPE_BUF bytes should be atomic, and then
                     // we want to be sure we *don't* run at_exit destructors as
                     // we're being torn down regardless
                     rtassert!(output.write(&bytes).is_ok());
                     libc::_exit(1)
                 }
                 n => n,
             }
         };

         let mut p = Process { pid, status: None };
         drop(output);
         let mut bytes = [0; 8];

         // loop to handle EINTR
         loop {
             match input.read(&mut bytes) {
                 Ok(0) => return Ok((p, ours)),
                 Ok(8) => {
                     let (errno, footer) = bytes.split_at(4);
                     assert_eq!(
                         CLOEXEC_MSG_FOOTER, footer,
                         "Validation on the CLOEXEC pipe failed: {:?}",
                         bytes
                     );
                     let errno = i32::from_be_bytes(errno.try_into().unwrap());
                     assert!(p.wait().is_ok(), "wait() should either return Ok or panic");
                     return Err(Error::from_raw_os_error(errno));
                 }
                 Err(ref e) if e.kind() == ErrorKind::Interrupted => {}
                 Err(e) => {
                     assert!(p.wait().is_ok(), "wait() should either return Ok or panic");
                     panic!("the CLOEXEC pipe failed: {:?}", e)
                 }
                 Ok(..) => {
                     // pipe I/O up to PIPE_BUF bytes should be atomic
                     assert!(p.wait().is_ok(), "wait() should either return Ok or panic");
                     panic!("short read on the CLOEXEC pipe")
                 }
             }
         }
     }

     pub fn exec(&mut self, default: Stdio) -> io::Error {
         let envp = self.capture_env();

         if self.saw_nul() {
             return io::Error::new(ErrorKind::InvalidInput, "nul byte found in provided data");
         }

         match self.setup_io(default, true) {
             Ok((_, theirs)) => {
                 unsafe {
                     // Similar to when forking, we want to ensure that access to
                     // the environment is synchronized, so make sure to grab the
                     // environment lock before we try to exec.
                     let _lock = sys::os::env_lock();

                     let Err(e) = self.do_exec(theirs, envp.as_ref());
                     e
                 }
             }
             Err(e) => e,
         }
     }

     // And at this point we've reached a special time in the life of the
     // child. The child must now be considered hamstrung and unable to
     // do anything other than syscalls really. Consider the following
     // scenario:
     //
     //      1. Thread A of process 1 grabs the malloc() mutex
     //      2. Thread B of process 1 forks(), creating thread C
     //      3. Thread C of process 2 then attempts to malloc()
     //      4. The memory of process 2 is the same as the memory of
     //         process 1, so the mutex is locked.
     //
     // This situation looks a lot like deadlock, right? It turns out
     // that this is what pthread_atfork() takes care of, which is
     // presumably implemented across platforms. The first thing that
     // threads to *before* forking is to do things like grab the malloc
     // mutex, and then after the fork they unlock it.
     //
     // Despite this information, libnative's spawn has been witnessed to
     // deadlock on both macOS and FreeBSD. I'm not entirely sure why, but
     // all collected backtraces point at malloc/free traffic in the
     // child spawned process.
     //
     // For this reason, the block of code below should contain 0
     // invocations of either malloc of free (or their related friends).
     //
     // As an example of not having malloc/free traffic, we don't close
     // this file descriptor by dropping the FileDesc (which contains an
     // allocation). Instead we just close it manually. This will never
     // have the drop glue anyway because this code never returns (the
     // child will either exec() or invoke libc::exit)
     unsafe fn do_exec(
         &mut self,
         stdio: ChildPipes,
         maybe_envp: Option<&CStringArray>,
     ) -> Result<!, io::Error> {
         use crate::sys::{self, cvt_r};

         if let Some(fd) = stdio.stdin.fd() {
             cvt_r(|| libc::dup2(fd, libc::STDIN_FILENO))?;
         }
         if let Some(fd) = stdio.stdout.fd() {
             cvt_r(|| libc::dup2(fd, libc::STDOUT_FILENO))?;
         }
         if let Some(fd) = stdio.stderr.fd() {
             cvt_r(|| libc::dup2(fd, libc::STDERR_FILENO))?;
         }

         #[cfg(not(target_os = "l4re"))]
         {
             if let Some(u) = self.get_gid() {
                 cvt(libc::setgid(u as gid_t))?;
             }
             if let Some(u) = self.get_uid() {
                 // When dropping privileges from root, the `setgroups` call
                 // will remove any extraneous groups. If we don't call this,
                 // then even though our uid has dropped, we may still have
                 // groups that enable us to do super-user things. This will
                 // fail if we aren't root, so don't bother checking the
                 // return value, this is just done as an optimistic
                 // privilege dropping function.
                 //FIXME: Redox kernel does not support setgroups yet
                 #[cfg(not(target_os = "redox"))]
                 let _ = libc::setgroups(0, ptr::null());
                 cvt(libc::setuid(u as uid_t))?;
             }
         }
         if let Some(ref cwd) = *self.get_cwd() {
             cvt(libc::chdir(cwd.as_ptr()))?;
         }

         // emscripten has no signal support.
         #[cfg(not(target_os = "emscripten"))]
         {
             use crate::mem::MaybeUninit;
             // Reset signal handling so the child process starts in a
             // standardized state. libstd ignores SIGPIPE, and signal-handling
             // libraries often set a mask. Child processes inherit ignored
             // signals and the signal mask from their parent, but most
             // UNIX programs do not reset these things on their own, so we
             // need to clean things up now to avoid confusing the program
             // we're about to run.
             let mut set = MaybeUninit::<libc::sigset_t>::uninit();
             cvt(sigemptyset(set.as_mut_ptr()))?;
             cvt(libc::pthread_sigmask(libc::SIG_SETMASK, set.as_ptr(), ptr::null_mut()))?;
             let ret = sys::signal(libc::SIGPIPE, libc::SIG_DFL);
             if ret == libc::SIG_ERR {
                 return Err(io::Error::last_os_error());
             }
         }

         for callback in self.get_closures().iter_mut() {
             callback()?;
         }

         // Although we're performing an exec here we may also return with an
         // error from this function (without actually exec'ing) in which case we
         // want to be sure to restore the global environment back to what it
         // once was, ensuring that our temporary override, when free'd, doesn't
         // corrupt our process's environment.
         let mut _reset = None;
         if let Some(envp) = maybe_envp {
             struct Reset(*const *const libc::c_char);

             impl Drop for Reset {
                 fn drop(&mut self) {
                     unsafe {
                         *sys::os::environ() = self.0;
                     }
                 }
             }

             _reset = Some(Reset(*sys::os::environ()));
             *sys::os::environ() = envp.as_ptr();
         }

         libc::execvp(self.get_program_cstr().as_ptr(), self.get_argv().as_ptr());
         Err(io::Error::last_os_error())
     }

     #[cfg(not(any(
         target_os = "macos",
         target_os = "freebsd",
         all(target_os = "linux", target_env = "gnu"),
         all(target_os = "linux", target_env = "musl"),
     )))]
     fn posix_spawn(
         &mut self,
         _: &ChildPipes,
         _: Option<&CStringArray>,
     ) -> io::Result<Option<Process>> {
         Ok(None)
     }

     // Only support platforms for which posix_spawn() can return ENOENT
     // directly.
     #[cfg(any(
         target_os = "macos",
         target_os = "freebsd",
         all(target_os = "linux", target_env = "gnu"),
         all(target_os = "linux", target_env = "musl"),
     ))]
     fn posix_spawn(
         &mut self,
         stdio: &ChildPipes,
         envp: Option<&CStringArray>,
     ) -> io::Result<Option<Process>> {
         use crate::mem::MaybeUninit;
         use crate::sys::{self, cvt_nz};

         if self.get_gid().is_some()
             || self.get_uid().is_some()
             || (self.env_saw_path() && !self.program_is_path())
             || !self.get_closures().is_empty()
         {
             return Ok(None);
         }

         // Only glibc 2.24+ posix_spawn() supports returning ENOENT directly.
         #[cfg(all(target_os = "linux", target_env = "gnu"))]
         {
             if let Some(version) = sys::os::glibc_version() {
                 if version < (2, 24) {
                     return Ok(None);
                 }
             } else {
                 return Ok(None);
             }
         }

         // Solaris, glibc 2.29+, and musl 1.24+ can set a new working directory,
         // and maybe others will gain this non-POSIX function too. We'll check
         // for this weak symbol as soon as it's needed, so we can return early
         // otherwise to do a manual chdir before exec.
         weak! {
             fn posix_spawn_file_actions_addchdir_np(
                 *mut libc::posix_spawn_file_actions_t,
                 *const libc::c_char
             ) -> libc::c_int
         }
         let addchdir = match self.get_cwd() {
             Some(cwd) => match posix_spawn_file_actions_addchdir_np.get() {
                 Some(f) => Some((f, cwd)),
                 None => return Ok(None),
             },
             None => None,
         };

         let mut p = Process { pid: 0, status: None };

         struct PosixSpawnFileActions<'a>(&'a mut MaybeUninit<libc::posix_spawn_file_actions_t>);

         impl Drop for PosixSpawnFileActions<'_> {
             fn drop(&mut self) {
                 unsafe {
                     libc::posix_spawn_file_actions_destroy(self.0.as_mut_ptr());
                 }
             }
         }

         struct PosixSpawnattr<'a>(&'a mut MaybeUninit<libc::posix_spawnattr_t>);

         impl Drop for PosixSpawnattr<'_> {
             fn drop(&mut self) {
                 unsafe {
                     libc::posix_spawnattr_destroy(self.0.as_mut_ptr());
                 }
             }
         }

         unsafe {
             let mut attrs = MaybeUninit::uninit();
             cvt_nz(libc::posix_spawnattr_init(attrs.as_mut_ptr()))?;
             let attrs = PosixSpawnattr(&mut attrs);

             let mut file_actions = MaybeUninit::uninit();
             cvt_nz(libc::posix_spawn_file_actions_init(file_actions.as_mut_ptr()))?;
             let file_actions = PosixSpawnFileActions(&mut file_actions);

             if let Some(fd) = stdio.stdin.fd() {
                 cvt_nz(libc::posix_spawn_file_actions_adddup2(
                     file_actions.0.as_mut_ptr(),
                     fd,
                     libc::STDIN_FILENO,
                 ))?;
             }
             if let Some(fd) = stdio.stdout.fd() {
                 cvt_nz(libc::posix_spawn_file_actions_adddup2(
                     file_actions.0.as_mut_ptr(),
                     fd,
                     libc::STDOUT_FILENO,
                 ))?;
             }
             if let Some(fd) = stdio.stderr.fd() {
                 cvt_nz(libc::posix_spawn_file_actions_adddup2(
                     file_actions.0.as_mut_ptr(),
                     fd,
                     libc::STDERR_FILENO,
                 ))?;
             }
             if let Some((f, cwd)) = addchdir {
                 cvt_nz(f(file_actions.0.as_mut_ptr(), cwd.as_ptr()))?;
             }

             let mut set = MaybeUninit::<libc::sigset_t>::uninit();
             cvt(sigemptyset(set.as_mut_ptr()))?;
             cvt_nz(libc::posix_spawnattr_setsigmask(attrs.0.as_mut_ptr(), set.as_ptr()))?;
             cvt(sigaddset(set.as_mut_ptr(), libc::SIGPIPE))?;
             cvt_nz(libc::posix_spawnattr_setsigdefault(attrs.0.as_mut_ptr(), set.as_ptr()))?;

             let flags = libc::POSIX_SPAWN_SETSIGDEF | libc::POSIX_SPAWN_SETSIGMASK;
             cvt_nz(libc::posix_spawnattr_setflags(attrs.0.as_mut_ptr(), flags as _))?;

             // Make sure we synchronize access to the global `environ` resource
             let _env_lock = sys::os::env_lock();
             let envp = envp.map(|c| c.as_ptr()).unwrap_or_else(|| *sys::os::environ() as *const _);
             cvt_nz(libc::posix_spawnp(
                 &mut p.pid,
                 self.get_program_cstr().as_ptr(),
                 file_actions.0.as_ptr(),
                 attrs.0.as_ptr(),
                 self.get_argv().as_ptr() as *const _,
                 envp as *const _,
             ))?;
             Ok(Some(p))
         }
     }
 }

 ////////////////////////////////////////////////////////////////////////////////
 // Processes
 ////////////////////////////////////////////////////////////////////////////////

 /// The unique ID of the process (this should never be negative).
 pub struct Process {
     pid: pid_t,
     status: Option<ExitStatus>,
 }

 impl Process {
     pub fn id(&self) -> u32 {
         self.pid as u32
     }

     pub fn kill(&mut self) -> io::Result<()> {
         // If we've already waited on this process then the pid can be recycled
         // and used for another process, and we probably shouldn't be killing
         // random processes, so just return an error.
         if self.status.is_some() {
             Err(Error::new(
                 ErrorKind::InvalidInput,
                 "invalid argument: can't kill an exited process",
             ))
         } else {
             cvt(unsafe { libc::kill(self.pid, libc::SIGKILL) }).map(drop)
         }
     }

     pub fn wait(&mut self) -> io::Result<ExitStatus> {
         use crate::sys::cvt_r;
         if let Some(status) = self.status {
             return Ok(status);
         }
         let mut status = 0 as c_int;
         cvt_r(|| unsafe { libc::waitpid(self.pid, &mut status, 0) })?;
         self.status = Some(ExitStatus::new(status));
         Ok(ExitStatus::new(status))
     }

     pub fn try_wait(&mut self) -> io::Result<Option<ExitStatus>> {
         if let Some(status) = self.status {
             return Ok(Some(status));
         }
         let mut status = 0 as c_int;
         let pid = cvt(unsafe { libc::waitpid(self.pid, &mut status, libc::WNOHANG) })?;
         if pid == 0 {
             Ok(None)
         } else {
             self.status = Some(ExitStatus::new(status));
             Ok(Some(ExitStatus::new(status)))
         }
     }
 }

 /// Unix exit statuses
 #[derive(PartialEq, Eq, Clone, Copy, Debug)]
 pub struct ExitStatus(c_int);

 impl ExitStatus {
     pub fn new(status: c_int) -> ExitStatus {
         ExitStatus(status)
     }

     fn exited(&self) -> bool {
         libc::WIFEXITED(self.0)
     }

     pub fn success(&self) -> bool {
         self.code() == Some(0)
     }

     pub fn code(&self) -> Option<i32> {
         if self.exited() { Some(libc::WEXITSTATUS(self.0)) } else { None }
     }

     pub fn signal(&self) -> Option<i32> {
         if !self.exited() { Some(libc::WTERMSIG(self.0)) } else { None }
     }
 }

 /// Converts a raw `c_int` to a type-safe `ExitStatus` by wrapping it without copying.
 impl From<c_int> for ExitStatus {
     fn from(a: c_int) -> ExitStatus {
         ExitStatus(a)
     }
 }

 impl fmt::Display for ExitStatus {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         if let Some(code) = self.code() {
             write!(f, "exit code: {}", code)
         } else {
             let signal = self.signal().unwrap();
             write!(f, "signal: {}", signal)
         }
     }
 }
	use crate::convert::TryInto;
	use crate::fmt;
	use crate::io::{self, Error, ErrorKind};
	use crate::ptr;
	use crate::sys;
	use crate::sys::cvt;
	use crate::sys::process::process_common::*;

	#[cfg(target_os = "vxworks")]
	use libc::RTP_ID as pid_t;

	#[cfg(not(target_os = "vxworks"))]
	use libc::{c_int, gid_t, pid_t, uid_t};

	////////////////////////////////////////////////////////////////////////////////
	// Command
	////////////////////////////////////////////////////////////////////////////////

	impl Command {
	pub fn spawn(
	&mut self,
	default: Stdio,
	needs_stdin: bool,
	) -> io::Result<(Process, StdioPipes)> {
	const CLOEXEC_MSG_FOOTER: [u8; 4] = *b"NOEX";

	let envp = self.capture_env();

	if self.saw_nul() {
	return Err(io::Error::new(ErrorKind::InvalidInput, "nul byte found in provided data"));
	}

	let (ours, theirs) = self.setup_io(default, needs_stdin)?;

	if let Some(ret) = self.posix_spawn(&theirs, envp.as_ref())? {
	return Ok((ret, ours));
	}

	let (input, output) = sys::pipe::anon_pipe()?;

	// Whatever happens after the fork is almost for sure going to touch or
	// look at the environment in one way or another (PATH in `execvp` or
	// accessing the `environ` pointer ourselves). Make sure no other thread
	// is accessing the environment when we do the fork itself.
	//
	// Note that as soon as we're done with the fork there's no need to hold
	// a lock any more because the parent won't do anything and the child is
	// in its own process.
	let result = unsafe {
	let _env_lock = sys::os::env_lock();
	cvt(libc::fork())?
	};

	let pid = unsafe {
	match result {
	0 => {
	drop(input);
	let Err(err) = self.do_exec(theirs, envp.as_ref());
	let errno = err.raw_os_error().unwrap_or(libc::EINVAL) as u32;
	let errno = errno.to_be_bytes();
	let bytes = [
	errno[0],
	errno[1],
	errno[2],
	errno[3],
	CLOEXEC_MSG_FOOTER[0],
	CLOEXEC_MSG_FOOTER[1],
	CLOEXEC_MSG_FOOTER[2],
	CLOEXEC_MSG_FOOTER[3],
	];
	// pipe I/O up to PIPE_BUF bytes should be atomic, and then
	// we want to be sure we don't run at_exit destructors as
	// we're being torn down regardless
	rtassert!(output.write(&bytes).is_ok());
	libc::_exit(1)
	}
	n => n,
	}
	};

	let mut p = Process { pid, status: None };
	drop(output);
	let mut bytes = [0; 8];

	// loop to handle EINTR
	loop {
	match input.read(&mut bytes) {
	Ok(0) => return Ok((p, ours)),
	Ok(8) => {
	let (errno, footer) = bytes.split_at(4);
	assert_eq!(
	CLOEXEC_MSG_FOOTER, footer,
	"Validation on the CLOEXEC pipe failed: {:?}",
	bytes
	);
	let errno = i32::from_be_bytes(errno.try_into().unwrap());
	assert!(p.wait().is_ok(), "wait() should either return Ok or panic");
	return Err(Error::from_raw_os_error(errno));
	}
	Err(ref e) if e.kind() == ErrorKind::Interrupted => {}
	Err(e) => {
	assert!(p.wait().is_ok(), "wait() should either return Ok or panic");
	panic!("the CLOEXEC pipe failed: {:?}", e)
	}
	Ok(..) => {
	// pipe I/O up to PIPE_BUF bytes should be atomic
	assert!(p.wait().is_ok(), "wait() should either return Ok or panic");
	panic!("short read on the CLOEXEC pipe")
	}
	}
	}
	}

	pub fn exec(&mut self, default: Stdio) -> io::Error {
	let envp = self.capture_env();

	if self.saw_nul() {
	return io::Error::new(ErrorKind::InvalidInput, "nul byte found in provided data");
	}

	match self.setup_io(default, true) {
	Ok((_, theirs)) => {
	unsafe {
	// Similar to when forking, we want to ensure that access to
	// the environment is synchronized, so make sure to grab the
	// environment lock before we try to exec.
	let _lock = sys::os::env_lock();

	let Err(e) = self.do_exec(theirs, envp.as_ref());
	e
	}
	}
	Err(e) => e,
	}
	}

	// And at this point we've reached a special time in the life of the
	// child. The child must now be considered hamstrung and unable to
	// do anything other than syscalls really. Consider the following
	// scenario:
	//
	// 1. Thread A of process 1 grabs the malloc() mutex
	// 2. Thread B of process 1 forks(), creating thread C
	// 3. Thread C of process 2 then attempts to malloc()
	// 4. The memory of process 2 is the same as the memory of
	// process 1, so the mutex is locked.
	//
	// This situation looks a lot like deadlock, right? It turns out
	// that this is what pthread_atfork() takes care of, which is
	// presumably implemented across platforms. The first thing that
	// threads to before forking is to do things like grab the malloc
	// mutex, and then after the fork they unlock it.
	//
	// Despite this information, libnative's spawn has been witnessed to
	// deadlock on both macOS and FreeBSD. I'm not entirely sure why, but
	// all collected backtraces point at malloc/free traffic in the
	// child spawned process.
	//
	// For this reason, the block of code below should contain 0
	// invocations of either malloc of free (or their related friends).
	//
	// As an example of not having malloc/free traffic, we don't close
	// this file descriptor by dropping the FileDesc (which contains an
	// allocation). Instead we just close it manually. This will never
	// have the drop glue anyway because this code never returns (the
	// child will either exec() or invoke libc::exit)
	unsafe fn do_exec(
	&mut self,
	stdio: ChildPipes,
	maybe_envp: Option<&CStringArray>,
	) -> Result<!, io::Error> {
	use crate::sys::{self, cvt_r};

	if let Some(fd) = stdio.stdin.fd() {
	cvt_r(\|\| libc::dup2(fd, libc::STDIN_FILENO))?;
	}
	if let Some(fd) = stdio.stdout.fd() {
	cvt_r(\|\| libc::dup2(fd, libc::STDOUT_FILENO))?;
	}
	if let Some(fd) = stdio.stderr.fd() {
	cvt_r(\|\| libc::dup2(fd, libc::STDERR_FILENO))?;
	}

	#[cfg(not(target_os = "l4re"))]
	{
	if let Some(u) = self.get_gid() {
	cvt(libc::setgid(u as gid_t))?;
	}
	if let Some(u) = self.get_uid() {
	// When dropping privileges from root, the `setgroups` call
	// will remove any extraneous groups. If we don't call this,
	// then even though our uid has dropped, we may still have
	// groups that enable us to do super-user things. This will
	// fail if we aren't root, so don't bother checking the
	// return value, this is just done as an optimistic
	// privilege dropping function.
	//FIXME: Redox kernel does not support setgroups yet
	#[cfg(not(target_os = "redox"))]
	let _ = libc::setgroups(0, ptr::null());
	cvt(libc::setuid(u as uid_t))?;
	}
	}
	if let Some(ref cwd) = *self.get_cwd() {
	cvt(libc::chdir(cwd.as_ptr()))?;
	}

	// emscripten has no signal support.
	#[cfg(not(target_os = "emscripten"))]
	{
	use crate::mem::MaybeUninit;
	// Reset signal handling so the child process starts in a
	// standardized state. libstd ignores SIGPIPE, and signal-handling
	// libraries often set a mask. Child processes inherit ignored
	// signals and the signal mask from their parent, but most
	// UNIX programs do not reset these things on their own, so we
	// need to clean things up now to avoid confusing the program
	// we're about to run.
	let mut set = MaybeUninit::<libc::sigset_t>::uninit();
	cvt(sigemptyset(set.as_mut_ptr()))?;
	cvt(libc::pthread_sigmask(libc::SIG_SETMASK, set.as_ptr(), ptr::null_mut()))?;
	let ret = sys::signal(libc::SIGPIPE, libc::SIG_DFL);
	if ret == libc::SIG_ERR {
	return Err(io::Error::last_os_error());
	}
	}

	for callback in self.get_closures().iter_mut() {
	callback()?;
	}

	// Although we're performing an exec here we may also return with an
	// error from this function (without actually exec'ing) in which case we
	// want to be sure to restore the global environment back to what it
	// once was, ensuring that our temporary override, when free'd, doesn't
	// corrupt our process's environment.
	let mut _reset = None;
	if let Some(envp) = maybe_envp {
	struct Reset(const const libc::c_char);

	impl Drop for Reset {
	fn drop(&mut self) {
	unsafe {
	*sys::os::environ() = self.0;
	}
	}
	}

	_reset = Some(Reset(*sys::os::environ()));
	*sys::os::environ() = envp.as_ptr();
	}

	libc::execvp(self.get_program_cstr().as_ptr(), self.get_argv().as_ptr());
	Err(io::Error::last_os_error())
	}

	#[cfg(not(any(
	target_os = "macos",
	target_os = "freebsd",
	all(target_os = "linux", target_env = "gnu"),
	all(target_os = "linux", target_env = "musl"),
	)))]
	fn posix_spawn(
	&mut self,
	_: &ChildPipes,
	_: Option<&CStringArray>,
	) -> io::Result<Option<Process>> {
	Ok(None)
	}

	// Only support platforms for which posix_spawn() can return ENOENT
	// directly.
	#[cfg(any(
	target_os = "macos",
	target_os = "freebsd",
	all(target_os = "linux", target_env = "gnu"),
	all(target_os = "linux", target_env = "musl"),
	))]
	fn posix_spawn(
	&mut self,
	stdio: &ChildPipes,
	envp: Option<&CStringArray>,
	) -> io::Result<Option<Process>> {
	use crate::mem::MaybeUninit;
	use crate::sys::{self, cvt_nz};

	if self.get_gid().is_some()
	\|\| self.get_uid().is_some()
	\|\| (self.env_saw_path() && !self.program_is_path())
	\|\| !self.get_closures().is_empty()
	{
	return Ok(None);
	}

	// Only glibc 2.24+ posix_spawn() supports returning ENOENT directly.
	#[cfg(all(target_os = "linux", target_env = "gnu"))]
	{
	if let Some(version) = sys::os::glibc_version() {
	if version < (2, 24) {
	return Ok(None);
	}
	} else {
	return Ok(None);
	}
	}

	// Solaris, glibc 2.29+, and musl 1.24+ can set a new working directory,
	// and maybe others will gain this non-POSIX function too. We'll check
	// for this weak symbol as soon as it's needed, so we can return early
	// otherwise to do a manual chdir before exec.
	weak! {
	fn posix_spawn_file_actions_addchdir_np(
	*mut libc::posix_spawn_file_actions_t,
	*const libc::c_char
	) -> libc::c_int
	}
	let addchdir = match self.get_cwd() {
	Some(cwd) => match posix_spawn_file_actions_addchdir_np.get() {
	Some(f) => Some((f, cwd)),
	None => return Ok(None),
	},
	None => None,
	};

	let mut p = Process { pid: 0, status: None };

	struct PosixSpawnFileActions<'a>(&'a mut MaybeUninit<libc::posix_spawn_file_actions_t>);

	impl Drop for PosixSpawnFileActions<'_> {
	fn drop(&mut self) {
	unsafe {
	libc::posix_spawn_file_actions_destroy(self.0.as_mut_ptr());
	}
	}
	}

	struct PosixSpawnattr<'a>(&'a mut MaybeUninit<libc::posix_spawnattr_t>);

	impl Drop for PosixSpawnattr<'_> {
	fn drop(&mut self) {
	unsafe {
	libc::posix_spawnattr_destroy(self.0.as_mut_ptr());
	}
	}
	}

	unsafe {
	let mut attrs = MaybeUninit::uninit();
	cvt_nz(libc::posix_spawnattr_init(attrs.as_mut_ptr()))?;
	let attrs = PosixSpawnattr(&mut attrs);

	let mut file_actions = MaybeUninit::uninit();
	cvt_nz(libc::posix_spawn_file_actions_init(file_actions.as_mut_ptr()))?;
	let file_actions = PosixSpawnFileActions(&mut file_actions);

	if let Some(fd) = stdio.stdin.fd() {
	cvt_nz(libc::posix_spawn_file_actions_adddup2(
	file_actions.0.as_mut_ptr(),
	fd,
	libc::STDIN_FILENO,
	))?;
	}
	if let Some(fd) = stdio.stdout.fd() {
	cvt_nz(libc::posix_spawn_file_actions_adddup2(
	file_actions.0.as_mut_ptr(),
	fd,
	libc::STDOUT_FILENO,
	))?;
	}
	if let Some(fd) = stdio.stderr.fd() {
	cvt_nz(libc::posix_spawn_file_actions_adddup2(
	file_actions.0.as_mut_ptr(),
	fd,
	libc::STDERR_FILENO,
	))?;
	}
	if let Some((f, cwd)) = addchdir {
	cvt_nz(f(file_actions.0.as_mut_ptr(), cwd.as_ptr()))?;
	}

	let mut set = MaybeUninit::<libc::sigset_t>::uninit();
	cvt(sigemptyset(set.as_mut_ptr()))?;
	cvt_nz(libc::posix_spawnattr_setsigmask(attrs.0.as_mut_ptr(), set.as_ptr()))?;
	cvt(sigaddset(set.as_mut_ptr(), libc::SIGPIPE))?;
	cvt_nz(libc::posix_spawnattr_setsigdefault(attrs.0.as_mut_ptr(), set.as_ptr()))?;

	let flags = libc::POSIX_SPAWN_SETSIGDEF \| libc::POSIX_SPAWN_SETSIGMASK;
	cvt_nz(libc::posix_spawnattr_setflags(attrs.0.as_mut_ptr(), flags as _))?;

	// Make sure we synchronize access to the global `environ` resource
	let _env_lock = sys::os::env_lock();
	let envp = envp.map(\|c\| c.as_ptr()).unwrap_or_else(\|\| sys::os::environ() as const _);
	cvt_nz(libc::posix_spawnp(
	&mut p.pid,
	self.get_program_cstr().as_ptr(),
	file_actions.0.as_ptr(),
	attrs.0.as_ptr(),
	self.get_argv().as_ptr() as *const _,
	envp as *const _,
	))?;
	Ok(Some(p))
	}
	}
	}

	////////////////////////////////////////////////////////////////////////////////
	// Processes
	////////////////////////////////////////////////////////////////////////////////

	/// The unique ID of the process (this should never be negative).
	pub struct Process {
	pid: pid_t,
	status: Option<ExitStatus>,
	}

	impl Process {
	pub fn id(&self) -> u32 {
	self.pid as u32
	}

	pub fn kill(&mut self) -> io::Result<()> {
	// If we've already waited on this process then the pid can be recycled
	// and used for another process, and we probably shouldn't be killing
	// random processes, so just return an error.
	if self.status.is_some() {
	Err(Error::new(
	ErrorKind::InvalidInput,
	"invalid argument: can't kill an exited process",
	))
	} else {
	cvt(unsafe { libc::kill(self.pid, libc::SIGKILL) }).map(drop)
	}
	}

	pub fn wait(&mut self) -> io::Result<ExitStatus> {
	use crate::sys::cvt_r;
	if let Some(status) = self.status {
	return Ok(status);
	}
	let mut status = 0 as c_int;
	cvt_r(\|\| unsafe { libc::waitpid(self.pid, &mut status, 0) })?;
	self.status = Some(ExitStatus::new(status));
	Ok(ExitStatus::new(status))
	}

	pub fn try_wait(&mut self) -> io::Result<Option<ExitStatus>> {
	if let Some(status) = self.status {
	return Ok(Some(status));
	}
	let mut status = 0 as c_int;
	let pid = cvt(unsafe { libc::waitpid(self.pid, &mut status, libc::WNOHANG) })?;
	if pid == 0 {
	Ok(None)
	} else {
	self.status = Some(ExitStatus::new(status));
	Ok(Some(ExitStatus::new(status)))
	}
	}
	}

	/// Unix exit statuses
	#[derive(PartialEq, Eq, Clone, Copy, Debug)]
	pub struct ExitStatus(c_int);

	impl ExitStatus {
	pub fn new(status: c_int) -> ExitStatus {
	ExitStatus(status)
	}

	fn exited(&self) -> bool {
	libc::WIFEXITED(self.0)
	}

	pub fn success(&self) -> bool {
	self.code() == Some(0)
	}

	pub fn code(&self) -> Option<i32> {
	if self.exited() { Some(libc::WEXITSTATUS(self.0)) } else { None }
	}

	pub fn signal(&self) -> Option<i32> {
	if !self.exited() { Some(libc::WTERMSIG(self.0)) } else { None }
	}
	}

	/// Converts a raw `c_int` to a type-safe `ExitStatus` by wrapping it without copying.
	impl From<c_int> for ExitStatus {
	fn from(a: c_int) -> ExitStatus {
	ExitStatus(a)
	}
	}

	impl fmt::Display for ExitStatus {
	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
	if let Some(code) = self.code() {
	write!(f, "exit code: {}", code)
	} else {
	let signal = self.signal().unwrap();
	write!(f, "signal: {}", signal)
	}
	}
	}