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|
//! Job management on Windows for bootstrapping
//!
//! Most of the time when you're running a build system (e.g., make) you expect
//! Ctrl-C or abnormal termination to actually terminate the entire tree of
//! process in play, not just the one at the top. This currently works "by
//! default" on Unix platforms because Ctrl-C actually sends a signal to the
//! *process group* rather than the parent process, so everything will get torn
//! down. On Windows, however, this does not happen and Ctrl-C just kills the
//! parent process.
//!
//! To achieve the same semantics on Windows we use Job Objects to ensure that
//! all processes die at the same time. Job objects have a mode of operation
//! where when all handles to the object are closed it causes all child
//! processes associated with the object to be terminated immediately.
//! Conveniently whenever a process in the job object spawns a new process the
//! child will be associated with the job object as well. This means if we add
//! ourselves to the job object we create then everything will get torn down!
//!
//! Unfortunately most of the time the build system is actually called from a
//! python wrapper (which manages things like building the build system) so this
//! all doesn't quite cut it so far. To go the last mile we duplicate the job
//! object handle into our parent process (a python process probably) and then
//! close our own handle. This means that the only handle to the job object
//! resides in the parent python process, so when python dies the whole build
//! system dies (as one would probably expect!).
//!
//! Note that this module has a #[cfg(windows)] above it as none of this logic
//! is required on Unix.
use crate::Build;
use std::env;
use std::ffi::c_void;
use std::io;
use std::mem;
use windows::{
core::PCWSTR,
Win32::Foundation::{CloseHandle, DuplicateHandle, DUPLICATE_SAME_ACCESS, HANDLE},
Win32::System::Diagnostics::Debug::{SetErrorMode, SEM_NOGPFAULTERRORBOX, THREAD_ERROR_MODE},
Win32::System::JobObjects::{
AssignProcessToJobObject, CreateJobObjectW, JobObjectExtendedLimitInformation,
SetInformationJobObject, JOBOBJECT_EXTENDED_LIMIT_INFORMATION,
JOB_OBJECT_LIMIT_KILL_ON_JOB_CLOSE, JOB_OBJECT_LIMIT_PRIORITY_CLASS,
},
Win32::System::Threading::{
GetCurrentProcess, OpenProcess, BELOW_NORMAL_PRIORITY_CLASS, PROCESS_DUP_HANDLE,
},
};
pub unsafe fn setup(build: &mut Build) {
// Enable the Windows Error Reporting dialog which msys disables,
// so we can JIT debug rustc
let mode = SetErrorMode(THREAD_ERROR_MODE::default());
let mode = THREAD_ERROR_MODE(mode);
SetErrorMode(mode & !SEM_NOGPFAULTERRORBOX);
// Create a new job object for us to use
let job = CreateJobObjectW(None, PCWSTR::null()).unwrap();
// Indicate that when all handles to the job object are gone that all
// process in the object should be killed. Note that this includes our
// entire process tree by default because we've added ourselves and our
// children will reside in the job by default.
let mut info = JOBOBJECT_EXTENDED_LIMIT_INFORMATION::default();
info.BasicLimitInformation.LimitFlags = JOB_OBJECT_LIMIT_KILL_ON_JOB_CLOSE;
if build.config.low_priority {
info.BasicLimitInformation.LimitFlags |= JOB_OBJECT_LIMIT_PRIORITY_CLASS;
info.BasicLimitInformation.PriorityClass = BELOW_NORMAL_PRIORITY_CLASS.0;
}
let r = SetInformationJobObject(
job,
JobObjectExtendedLimitInformation,
&info as *const _ as *const c_void,
mem::size_of_val(&info) as u32,
)
.ok();
assert!(r.is_ok(), "{}", io::Error::last_os_error());
// Assign our process to this job object. Note that if this fails, one very
// likely reason is that we are ourselves already in a job object! This can
// happen on the build bots that we've got for Windows, or if just anyone
// else is instrumenting the build. In this case we just bail out
// immediately and assume that they take care of it.
//
// Also note that nested jobs (why this might fail) are supported in recent
// versions of Windows, but the version of Windows that our bots are running
// at least don't support nested job objects.
let r = AssignProcessToJobObject(job, GetCurrentProcess()).ok();
if r.is_err() {
CloseHandle(job);
return;
}
// If we've got a parent process (e.g., the python script that called us)
// then move ownership of this job object up to them. That way if the python
// script is killed (e.g., via ctrl-c) then we'll all be torn down.
//
// If we don't have a parent (e.g., this was run directly) then we
// intentionally leak the job object handle. When our process exits
// (normally or abnormally) it will close the handle implicitly, causing all
// processes in the job to be cleaned up.
let pid = match env::var("BOOTSTRAP_PARENT_ID") {
Ok(s) => s,
Err(..) => return,
};
let parent = match OpenProcess(PROCESS_DUP_HANDLE, false, pid.parse().unwrap()).ok() {
Some(parent) => parent,
_ => {
// If we get a null parent pointer here, it is possible that either
// we have an invalid pid or the parent process has been closed.
// Since the first case rarely happens
// (only when wrongly setting the environmental variable),
// it might be better to improve the experience of the second case
// when users have interrupted the parent process and we haven't finish
// duplicating the handle yet. We just need close the job object if that occurs.
CloseHandle(job);
return;
}
};
let mut parent_handle = HANDLE::default();
let r = DuplicateHandle(
GetCurrentProcess(),
job,
parent,
&mut parent_handle,
0,
false,
DUPLICATE_SAME_ACCESS,
)
.ok();
// If this failed, well at least we tried! An example of DuplicateHandle
// failing in the past has been when the wrong python2 package spawned this
// build system (e.g., the `python2` package in MSYS instead of
// `mingw-w64-x86_64-python2`). Not sure why it failed, but the "failure
// mode" here is that we only clean everything up when the build system
// dies, not when the python parent does, so not too bad.
if r.is_err() {
CloseHandle(job);
}
}
|
