monochromatic-git-policy-cli 0.5.25

//! Controls for the meter and the clock of a push's progress, on real short-lived processes that write, sleep and start
//! others at known times.
//! Why:
//!  The stop on no progress is only as exact as the bytes it counts and the limits it keeps, so each is pinned on both sides:
//!  bytes of the root and of what it started count, an idle tree counts nothing, a moving tree never stalls, a stalled tree
//!  stops at its window, a trickle stops at its ceiling, and where nothing is measured the window is a fixed deadline.
//!
//! In TS you'd write (pseudocode):
//! ```ts
//! expect(meter.sample(pid)).toBe(true); await sleep(idle); expect(meter.sample(pid)).toBe(false);
//! ```
#![cfg(unix)]

use super::*;
use crate::test_support::{fixture, remove};
use std::process::{Child, Command, Stdio};
/// The name the control gives the probe test in order to run it as a process of its own.
const PROBE_NAME: &str = "push_progress::tests::disk_wait_probe";

/// The variable that holds the probe's hold in milliseconds; without it the probe does nothing.
const PROBE_HOLD_VARIABLE: &str = "CLI_GIT_DISK_WAIT_PROBE_HOLD_MILLISECONDS";

/// The variable that says what the probe does when its hold is over: `exit`, or `idle` to sleep as a process waiting on a server.
const PROBE_THEN_VARIABLE: &str = "CLI_GIT_DISK_WAIT_PROBE_THEN";

/// Pause between two looks of a control, shorter than every limit it uses.
const LOOK: Duration = Duration::from_millis(50);

/// How long a control waits for something that must happen, so a broken meter fails it and never holds it.
const PATIENCE: Duration = Duration::from_secs(20);

/// A shell command running `script` in `directory`, with its output discarded.
fn shell(script: &str, directory: &std::path::Path) -> Child {
    return Command::new("sh")
        .arg("-c")
        .arg(script)
        .current_dir(directory)
        .stdin(Stdio::null())
        .stdout(Stdio::null())
        .stderr(Stdio::null())
        .spawn()
        .expect("start the shell");
}

/// End a child the control started.
fn end(mut child: Child) {
    child.kill().expect("end the child");
    child.wait().expect("reap the child");
}

/// Look at the tree until a sample shows nothing new, which an idle tree does within a few looks of its start.
fn settle(meter: &mut Meter, root: i32) {
    let began: Instant = Instant::now();
    while meter.sample(root) {
        assert!(began.elapsed() < PATIENCE, "the tree never went idle");
        std::thread::sleep(LOOK);
    }
}

/// An idle tree moves nothing between looks, and a write of the root shows at the next look.
#[test]
fn a_write_of_the_root_is_progress_and_an_idle_tree_is_not() {
    let root: std::path::PathBuf = fixture("progress-root");
    let child: Child = shell("sleep 0.6; echo a >> log; sleep 60", root.as_path());
    let pid: i32 = i32::try_from(child.id()).expect("pid");
    let mut meter: Meter = Meter::new();
    settle(&mut meter, pid);
    let idle: u64 = meter.moved();
    assert!(!meter.sample(pid), "nothing moved between two looks of an idle tree");
    assert_eq!(meter.moved(), idle);
    let began: Instant = Instant::now();
    let mut seen: bool = false;
    while !seen && began.elapsed() < PATIENCE {
        std::thread::sleep(LOOK);
        seen = meter.sample(pid);
    }
    assert!(seen, "the write of the root was seen");
    assert!(meter.moved() > idle);
    end(child);
    remove(root.as_path());
}

/// What a process started by the root writes counts too: the root itself only waits.
#[test]
fn a_write_of_a_process_the_root_started_is_progress() {
    let root: std::path::PathBuf = fixture("progress-descendant");
    let child: Child = shell("(sleep 0.6; echo a >> log; sleep 60) & wait", root.as_path());
    let pid: i32 = i32::try_from(child.id()).expect("pid");
    let mut meter: Meter = Meter::new();
    settle(&mut meter, pid);
    let idle: u64 = meter.moved();
    let began: Instant = Instant::now();
    let mut seen: bool = false;
    while !seen && began.elapsed() < PATIENCE {
        std::thread::sleep(LOOK);
        seen = meter.sample(pid);
    }
    assert!(seen, "the write of the descendant was seen");
    assert!(meter.moved() > idle);
    end(child);
    remove(root.as_path());
}

/// A process that ends takes its counters with it, and the bytes it moved stay counted.
#[test]
fn the_bytes_of_a_process_that_ended_stay_counted() {
    let root: std::path::PathBuf = fixture("progress-ended");
    let child: Child = shell("(echo a >> log; echo b >> log) ; sleep 60", root.as_path());
    let pid: i32 = i32::try_from(child.id()).expect("pid");
    let mut meter: Meter = Meter::new();
    settle(&mut meter, pid);
    let counted: u64 = meter.moved();
    assert!(counted > 0, "the shell and its subshell moved bytes");
    assert!(!meter.sample(pid));
    assert_eq!(meter.moved(), counted, "a subshell that has ended does not take its bytes away");
    end(child);
    remove(root.as_path());
}

/// A process that does not exist moves nothing, and the system counts bytes for a process that does.
#[test]
fn a_missing_process_moves_nothing_and_this_system_counts_bytes() {
    assert_eq!(bytes_moved_by(i32::MAX), None);
    assert!(bytes_moved_by(i32::try_from(std::process::id()).expect("pid")).is_some());
    assert!(system_measures());
    assert!(!Meter::new().sample(i32::MAX));
}

/// A fixed patience stops at its limit, and not before.
#[test]
fn a_fixed_patience_stops_at_its_limit() {
    let child: Child = Command::new("sleep").arg("60").spawn().expect("sleep");
    let limit: Duration = Duration::from_millis(400);
    let mut clock: Clock = Clock::start(child.id(), Patience::Fixed(limit));
    let began: Instant = Instant::now();
    assert!(clock.check().is_none(), "not yet");
    let cause: StopCause = loop {
        if let Some(cause) = clock.check() {
            break cause;
        }
        assert!(began.elapsed() < PATIENCE);
        std::thread::sleep(LOOK);
    };
    assert!(matches!(cause, StopCause::Deadline));
    assert!(began.elapsed() >= limit);
    end(child);
}

/// A tree that moves nothing stalls at its window, with the window, the bytes moved and the time in the report.
#[test]
fn a_tree_that_moves_nothing_stalls_at_its_window() {
    let child: Child = Command::new("sleep").arg("60").spawn().expect("sleep");
    let stall: Duration = Duration::from_millis(1200);
    let mut clock: Clock = Clock::start(child.id(), Patience::Progress { stall, ceiling: Duration::from_secs(600) });
    let began: Instant = Instant::now();
    let cause: StopCause = loop {
        if let Some(cause) = clock.check() {
            break cause;
        }
        assert!(began.elapsed() < PATIENCE);
        std::thread::sleep(LOOK);
    };
    let StopCause::Stalled(report) = cause else { panic!("a stall, not another limit") };
    assert_eq!(report.limit, stall);
    assert!(report.elapsed >= stall, "{:?}", report.elapsed);
    assert!(report.elapsed < stall + SAMPLE_INTERVAL * 6, "{:?}", report.elapsed);
    end(child);
}

/// A tree that keeps moving never stalls, and a trickle stops at the ceiling with the ceiling in the report.
#[test]
fn a_tree_that_keeps_moving_stops_only_at_the_ceiling() {
    let root: std::path::PathBuf = fixture("progress-ceiling");
    let child: Child = shell("while :; do echo x >> log; sleep 0.1; done", root.as_path());
    let stall: Duration = Duration::from_millis(1500);
    let ceiling: Duration = Duration::from_millis(4000);
    let mut clock: Clock = Clock::start(child.id(), Patience::Progress { stall, ceiling });
    let began: Instant = Instant::now();
    let cause: StopCause = loop {
        if let Some(cause) = clock.check() {
            break cause;
        }
        assert!(began.elapsed() < PATIENCE);
        std::thread::sleep(LOOK);
    };
    let StopCause::Ceiling(report) = cause else { panic!("the ceiling, not a stall") };
    assert_eq!(report.limit, ceiling);
    assert!(report.elapsed >= ceiling, "the stall window of {stall:?} passed with data moving and nothing stopped it");
    assert!(report.moved > 0);
    end(child);
    remove(root.as_path());
}

/// Where nothing is measured the stall window is a fixed deadline, even for a tree that writes all the time.
#[test]
fn without_a_measure_the_stall_window_is_a_fixed_deadline() {
    let root: std::path::PathBuf = fixture("progress-unmeasured");
    let child: Child = shell("while :; do echo x >> log; sleep 0.1; done", root.as_path());
    let stall: Duration = Duration::from_millis(600);
    let mut clock: Clock = Clock::start(child.id(), Patience::Progress { stall, ceiling: Duration::from_secs(600) }).unmeasured();
    let began: Instant = Instant::now();
    let cause: StopCause = loop {
        if let Some(cause) = clock.check() {
            break cause;
        }
        assert!(began.elapsed() < PATIENCE);
        std::thread::sleep(LOOK);
    };
    assert!(matches!(cause, StopCause::Deadline), "no measure, so the window is the whole deadline");
    assert!(began.elapsed() >= stall);
    end(child);
    remove(root.as_path());
}

/// What the probe's child does for its hold: sleep, and end. The probe's thread is then blocked in `clone` with
///  `CLONE_VFORK`, which the kernel waits out in uninterruptible sleep (state `D`) without any disk, byte or processor time.
extern "C" fn hold_in_vfork_child(milliseconds: *mut libc::c_void) -> libc::c_int {
    let hold: usize = milliseconds as usize;
    let pause: libc::timespec = libc::timespec {
        tv_sec: libc::time_t::try_from(hold / 1000).unwrap_or(0),
        tv_nsec: libc::c_long::try_from((hold % 1000) * 1_000_000).unwrap_or(0),
    };
    // SAFETY: `nanosleep` and `_exit` are async-signal-safe and touch nothing of the parent but the stack this child owns;
    //  the child shares the parent's memory until it ends, so it calls nothing else.
    unsafe {
        libc::nanosleep(&pause, std::ptr::null_mut());
        libc::_exit(0);
    }
}

/// Hold the calling thread in uninterruptible sleep for `milliseconds`: no I/O, no processor time, no byte moved, which is
///  what a wait for a slow disk looks like to `/proc` and what no file system, device or FUSE mount is needed to make.
fn hold_in_disk_wait(milliseconds: usize) {
    let mut stack: Vec<u8> = vec![0; 64 * 1024];
    // SAFETY: the child gets its own stack (`stack` outlives the call, which returns only after the child ended) and runs
    //  `hold_in_vfork_child`, which only sleeps and exits; the parent waits for it with `waitpid` so no zombie is left.
    unsafe {
        let top: *mut libc::c_void = stack.as_mut_ptr().add(stack.len()).cast();
        let child: libc::pid_t =
            libc::clone(hold_in_vfork_child, top, libc::CLONE_VM | libc::CLONE_VFORK | libc::SIGCHLD, milliseconds as *mut libc::c_void);
        assert!(child > 0, "clone failed: {}", std::io::Error::last_os_error());
        libc::waitpid(child, std::ptr::null_mut(), 0);
    }
}

/// The process the controls start when they need a tree in disk wait: not a test of its own, it does nothing unless the
///  variable names a hold, and then holds a thread in uninterruptible sleep for that long and either ends or sleeps on.
#[test]
fn disk_wait_probe() {
    let Some(hold) = std::env::var(PROBE_HOLD_VARIABLE).ok().and_then(|text| { return text.parse::<usize>().ok(); }) else {
        return;
    };
    hold_in_disk_wait(hold);
    if std::env::var(PROBE_THEN_VARIABLE).as_deref() == Ok("idle") {
        std::thread::sleep(Duration::from_secs(600));
    }
}

/// The command that runs the probe: this test binary, the probe only, holding for `hold`, then `then`.
pub(crate) fn disk_wait_command(hold: Duration, then: &str) -> Command {
    #[allow(clippy::disallowed_methods, reason = "identifies the running test binary so the control can start the probe test of it as a process of its own")]
    let test_binary: std::path::PathBuf = std::env::current_exe().expect("this test binary");
    let mut command: Command = Command::new(test_binary);
    command
        .args(["--exact", PROBE_NAME, "--nocapture", "--test-threads", "1"])
        .env(PROBE_HOLD_VARIABLE, hold.as_millis().to_string())
        .env(PROBE_THEN_VARIABLE, then)
        .stdin(Stdio::null());
    return command;
}

/// A thread in uninterruptible sleep is a sign of life at every look, with nothing else moving: the wait of a process for
///  its disk (the fsync of an object, the update of a ref) is not a stall. The probe's hold ends and it sleeps on, and then
///  the tree is idle at last.
#[test]
fn a_tree_in_disk_wait_is_progress_at_every_look_until_it_ends() {
    let mut probe: Command = disk_wait_command(Duration::from_millis(3000), "idle");
    probe.stdout(Stdio::null()).stderr(Stdio::null());
    let child: Child = probe.spawn().expect("start the probe");
    let pid: i32 = i32::try_from(child.id()).expect("pid");
    let mut meter: Meter = Meter::new();
    // The probe starts up and works for a moment first; the looks below fall in its hold or in that start-up, both alive.
    std::thread::sleep(Duration::from_millis(700));
    for look in 0..4 {
        std::thread::sleep(Duration::from_millis(400));
        assert!(meter.sample(pid), "look {look}: a thread in uninterruptible sleep is alive");
    }
    let began: Instant = Instant::now();
    let mut idle: bool = false;
    while !idle && began.elapsed() < PATIENCE {
        std::thread::sleep(Duration::from_millis(400));
        idle = !meter.sample(pid);
    }
    assert!(idle, "once the hold is over and the probe sleeps, the tree is idle");
    end(child);
}

/// A push-like tree in disk wait for longer than the stall window is not stopped, and one that sleeps on afterwards is.
#[test]
fn a_clock_does_not_stall_a_tree_in_disk_wait_and_stalls_it_after() {
    let mut probe: Command = disk_wait_command(Duration::from_millis(4000), "idle");
    probe.stdout(Stdio::null()).stderr(Stdio::null());
    let child: Child = probe.spawn().expect("start the probe");
    let stall: Duration = Duration::from_millis(1500);
    let mut clock: Clock = Clock::start(child.id(), Patience::Progress { stall, ceiling: Duration::from_secs(600) });
    // The probe's own start-up counts as work; the hold begins after it and lasts well past the window.
    let began: Instant = Instant::now();
    let cause: StopCause = loop {
        if let Some(cause) = clock.check() {
            break cause;
        }
        assert!(began.elapsed() < PATIENCE);
        std::thread::sleep(LOOK);
    };
    let StopCause::Stalled(report) = cause else { panic!("a stall, not another limit") };
    assert!(
        report.elapsed >= Duration::from_millis(4000),
        "the hold of 4 s in disk wait is no stall, and the stall came only after it: {:?}",
        report.elapsed
    );
    end(child);
}

/// A `/proc/<pid>/stat` line is read after its last parenthesis: the state, and the user and system ticks added.
#[test]
fn a_stat_line_gives_its_state_and_its_processor_ticks() {
    let line: &str = "4242 (a (odd) name) D 1 4242 4242 0 -1 4194560 100 0 0 0 7 5 0 0 20 0 1 0 12345 1000 10 18446744073709551615";
    assert_eq!(parse_activity(line), Some(('D', 12)));
    assert_eq!(parse_activity("1 (x) S 0 1"), None, "a line cut short gives nothing");
    assert_eq!(parse_activity("no parenthesis"), None);
    assert!(is_working('R') && is_working('D'));
    for resting in ['S', 'T', 't', 'Z', 'I'] {
        assert!(!is_working(resting), "{resting}");
    }
}

/// Each sign of work counts alone, at the look that finds it, and a process that shows none is idle: bytes, processor ticks,
///  a task able to run or waiting for the disk.
#[test]
fn each_sign_of_work_counts_alone_and_nothing_counts_for_nothing() {
    let key: (i32, u64) = (100, 1);
    let mut meter: Meter = Meter::new();
    assert!(!meter.observe(key, 0, 0, false), "a process that has done nothing is idle at its first look");
    assert!(!meter.observe(key, 0, 0, false));
    assert!(meter.observe(key, 10, 0, false), "bytes");
    assert_eq!(meter.moved(), 10);
    assert!(!meter.observe(key, 10, 0, false), "the same bytes are not new work");
    assert!(meter.observe(key, 10, 1, false), "one processor tick");
    assert!(!meter.observe(key, 10, 1, false));
    assert!(meter.observe(key, 10, 1, true), "a task able to run or waiting for the disk, at every look it is found");
    assert!(meter.observe(key, 10, 1, true));
    assert!(!meter.observe(key, 10, 1, false), "and idle when it is not");
    assert_eq!(meter.moved(), 10, "processor time and states are not bytes");
    assert!(meter.observe((200, 1), 0, 3, false), "a new process that has already used time");
    assert!(!meter.observe(key, 5, 1, false), "a counter that fell (a number reused) is not work");
}