bootstrap/utils/
job.rs

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
#[cfg(windows)]
pub use for_windows::*;

#[cfg(any(target_os = "haiku", target_os = "hermit", not(any(unix, windows))))]
pub unsafe fn setup(_build: &mut crate::Build) {}

#[cfg(all(unix, not(target_os = "haiku")))]
pub unsafe fn setup(build: &mut crate::Build) {
    if build.config.low_priority {
        libc::setpriority(libc::PRIO_PGRP as _, 0, 10);
    }
}

/// 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
/// processes in play. This currently works "by
/// default" on Unix platforms because Ctrl-C actually sends a signal to the
/// *process group* so everything will get torn
/// down. On Windows, however, Ctrl-C is only sent to processes in the same console.
/// If a process is detached or attached to another console, it won't receive the
/// signal.
///
/// 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 is a Windows specific module as none of this logic is required on Unix.
#[cfg(windows)]
mod for_windows {
    use std::ffi::c_void;
    use std::{env, io, mem};

    use windows::Win32::Foundation::{CloseHandle, DUPLICATE_SAME_ACCESS, DuplicateHandle, HANDLE};
    use windows::Win32::System::Diagnostics::Debug::{
        SEM_NOGPFAULTERRORBOX, SetErrorMode, THREAD_ERROR_MODE,
    };
    use windows::Win32::System::JobObjects::{
        AssignProcessToJobObject, CreateJobObjectW, JOB_OBJECT_LIMIT_KILL_ON_JOB_CLOSE,
        JOB_OBJECT_LIMIT_PRIORITY_CLASS, JOBOBJECT_EXTENDED_LIMIT_INFORMATION,
        JobObjectExtendedLimitInformation, SetInformationJobObject,
    };
    use windows::Win32::System::Threading::{
        BELOW_NORMAL_PRIORITY_CLASS, GetCurrentProcess, OpenProcess, PROCESS_DUP_HANDLE,
    };
    use windows::core::PCWSTR;

    use crate::Build;

    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,
        );
        assert!(r.is_ok(), "{}", io::Error::last_os_error());

        // Assign our process to this job object.
        let r = AssignProcessToJobObject(job, GetCurrentProcess());
        if r.is_err() {
            CloseHandle(job).ok();
            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.
                return;
            }
        };

        let mut parent_handle = HANDLE::default();
        // If this fails, 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.
        let _ = DuplicateHandle(
            GetCurrentProcess(),
            job,
            parent,
            &mut parent_handle,
            0,
            false,
            DUPLICATE_SAME_ACCESS,
        );
        CloseHandle(parent).ok();
    }
}