Segfault when watcher is moved.

[TyOverby]

I have a program written using rsnotify 2.3.3 that segfaults when I touch a file that I'm watching.

Here's the backtrace from lldb

Process 60876 stopped
* thread #2: tid = 0x2b2995, 0x00000001000e36f8 stormtrooper`notify::sync::mpsc::oneshot::Packet<T>::sent(self=0x0000000000000010) + 8 at oneshot.rs:133, stop reason = EXC_BAD_ACCESS (code=1, address=0x60)
    frame #0: 0x00000001000e36f8 stormtrooper`notify::sync::mpsc::oneshot::Packet<T>::sent(self=0x0000000000000010) + 8 at oneshot.rs:133
(lldb) bt
error: need to add support for DW_TAG_base_type '()' encoded with DW_ATE = 0x7, bit_size = 0
* thread #2: tid = 0x2b2995, 0x00000001000e36f8 stormtrooper`notify::sync::mpsc::oneshot::Packet<T>::sent(self=0x0000000000000010) + 8 at oneshot.rs:133, stop reason = EXC_BAD_ACCESS (code=1, address=0x60)
  * frame #0: 0x00000001000e36f8 stormtrooper`notify::sync::mpsc::oneshot::Packet<T>::sent(self=0x0000000000000010) + 8 at oneshot.rs:133
    frame #1: 0x00000001000e2b95 stormtrooper`notify::sync::mpsc::Sender<T>::send(self=0x00007fff5fbff8e0, t=Event at 0x0000000101cfa618) + 517 at mod.rs:535
    frame #2: 0x00000001000e1c41 stormtrooper`notify::fsevent::callback(stream_ref=0x0000000101a002b0, info=0x00007fff5fbff8e0, num_events=1, event_paths=0x0000000101a00780, event_flags=0x00000001005f1000, event_ids=0x00000001005f0000) + 1649 at fsevent.rs:197
    frame #3: 0x00000001000dbf6d stormtrooper`fsevent::callback::hf1094fd0c5c09dbeeia + 61
    frame #4: 0x00007fff92498ba1 FSEvents`implementation_callback_rpc + 2123
    frame #5: 0x00007fff92496672 FSEvents`_Xcallback_rpc + 254
    frame #6: 0x00007fff92496746 FSEvents`FSEventsD2F_server + 54
    frame #7: 0x00007fff9249bf75 FSEvents`FSEventsClientProcessMessageCallback + 44
    frame #8: 0x00007fff88de8d87 CoreFoundation`__CFMachPortPerform + 247
    frame #9: 0x00007fff88de8c79 CoreFoundation`__CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 41
    frame #10: 0x00007fff88de8beb CoreFoundation`__CFRunLoopDoSource1 + 475
    frame #11: 0x00007fff88dda767 CoreFoundation`__CFRunLoopRun + 2375
    frame #12: 0x00007fff88dd9bd8 CoreFoundation`CFRunLoopRunSpecific + 296
    frame #13: 0x00007fff88e91671 CoreFoundation`CFRunLoopRun + 97
    frame #14: 0x00000001000de91a stormtrooper`fnfn + 410 at fsevent.rs:158
    frame #15: 0x00000001000de749 stormtrooper`notify::boxed::F.FnBox<A>::call_box(self=0x0000000101437030, args=<unavailable>) + 89 at boxed.rs:516
    frame #16: 0x00000001000de33c stormtrooper`notify::boxed::Box<FnBox<A, Output = R>+ Send + 'a>.FnOnce<A>::call_once(self=Box<FnBox<()>> at 0x0000000101d00bc0, args=<unavailable>) + 60 at boxed.rs:532
    frame #17: 0x00000001000ddf0e stormtrooper`fnfn + 78 at mod.rs:281
    frame #18: 0x00000001000ddeba stormtrooper`notify::sys_common::unwind::try::try_fn<closure>(opt_closure=0x0000000101d00cf0) + 58 at mod.rs:156
    frame #19: 0x00000001001a7e89 stormtrooper`__rust_try + 9
    frame #20: 0x00000001001a59cf stormtrooper`sys_common::unwind::try::inner_try::h9c69b1952218bc71tRr + 111
    frame #21: 0x00000001000dde24 stormtrooper`notify::sys_common::unwind::try<closure>(f=closure at 0x0000000101d00d08) + 100 at mod.rs:126
    frame #22: 0x00000001000ddc9c stormtrooper`fnfn + 412 at mod.rs:281
    frame #23: 0x00000001000de56d stormtrooper`notify::boxed::F.FnBox<A>::call_box(self=0x000000010143b000, args=<unavailable>) + 77 at boxed.rs:516
    frame #24: 0x00000001001a955e stormtrooper`sys::thread::_$LT$impl$GT$::new::thread_start::h08e832c9db3841f0Qcw + 142
    frame #25: 0x00007fff8aba805a libsystem_pthread.dylib`_pthread_body + 131
    frame #26: 0x00007fff8aba7fd7 libsystem_pthread.dylib`_pthread_start + 176
    frame #27: 0x00007fff8aba53ed libsystem_pthread.dylib`thread_start + 13

[TyOverby]

Here's how I'm using rsnotify:

fn watch(file: &str) {
    use notify::{RecommendedWatcher, Error, Watcher};
    use std::sync::mpsc::channel;
    use std::thread;

    // Create a channel to receive the events.
    let (tx, rx) = channel();

    let mut watcher = notify::new(tx).unwrap();
    watcher.watch(file).unwrap();

    thread::spawn(move || {
        match rx.recv() {
            _ => println!("changes!")
        }
    });
}

fn main() {
    watch("./test.ares");
}

[passcod]

Pinging @octplane on this.

[octplane]

Can't reproduce using this very code:

extern crate notify;

fn watch(file: &str) {
    use notify::Watcher;
    use std::sync::mpsc::channel;
    use std::thread;

    // Create a channel to receive the events.
    let (tx, rx) = channel();

    let mut watcher = notify::new(tx).unwrap();
    watcher.watch(file).unwrap();

    let _ = thread::spawn(move || {
        loop {
        match rx.recv() {
            _ => println!("changes!")
        }
        }
    }).join();

}

fn main() {
    watch("./test.ares");
}

I'm using rustc 1.3.0 (9a92aaf19 2015-09-15), with a blank project only using rsnotify-2.3.3.
@TyOverby can you try narrowing down the issue on your side ?

[TyOverby]

@octplane Ah, sorry about that, it looks like the issue was based around how threading and dropping the watcher interact.

Here's my repro using rsnotify-2.3.3 and rustc 1.5.0-nightly (81b3b27cf 2015-10-11).

extern crate notify;

fn watch(file: &str) -> notify::FsEventWatcher {
    use notify::Watcher;
    use std::sync::mpsc::channel;
    use std::thread;

    // Create a channel to receive the events.
    let (tx, rx) = channel();

    let mut watcher = notify::new(tx).unwrap();
    watcher.watch(file).unwrap();

    // Don't join this thread
    thread::spawn(move || {
        loop {
        match rx.recv() {
            _ => println!("changes!")
        }
        }
    });

    watcher
}

fn main() {
    // Don't let the watcher drop
    let _watcher = watch("./test.ares");
    // in my real application, this sleep-loop
    // is actually a webserver that is running
    loop {
        ::std::thread::sleep_ms(20);
    }
}

LLDB stacktrace

(lldb) target create "target/debug/rsnotify-repro"
Current executable set to 'target/debug/rsnotify-repro' (x86_64).
(lldb) run
Process 78741 launched: '/Users/tyoverby/workspace/rust/rsnotify-repro/target/debug/rsnotify-repro' (x86_64)
Process 78741 stopped
* thread #2: tid = 0x2cdd9c, 0x0000000100034e68 rsnotify-repro`notify::sync::mpsc::oneshot::Packet<T>::sent(self=0x0000000000001010) + 8 at oneshot.rs:133, stop reason = EXC_BAD_ACCESS (code=1, address=0x1060)
    frame #0: 0x0000000100034e68 rsnotify-repro`notify::sync::mpsc::oneshot::Packet<T>::sent(self=0x0000000000001010) + 8 at oneshot.rs:133
(lldb) bt
error: need to add support for DW_TAG_base_type '()' encoded with DW_ATE = 0x7, bit_size = 0
* thread #2: tid = 0x2cdd9c, 0x0000000100034e68 rsnotify-repro`notify::sync::mpsc::oneshot::Packet<T>::sent(self=0x0000000000001010) + 8 at oneshot.rs:133, stop reason = EXC_BAD_ACCESS (code=1, address=0x1060)
  * frame #0: 0x0000000100034e68 rsnotify-repro`notify::sync::mpsc::oneshot::Packet<T>::sent(self=0x0000000000001010) + 8 at oneshot.rs:133
    frame #1: 0x0000000100034305 rsnotify-repro`notify::sync::mpsc::Sender<T>::send(self=0x00007fff5fbff8d0, t=Event at 0x00000001039fa618) + 517 at mod.rs:535
    frame #2: 0x00000001000333b1 rsnotify-repro`notify::fsevent::callback(stream_ref=0x0000000100500c50, info=0x00007fff5fbff8d0, num_events=1, event_paths=0x0000000100700140, event_flags=0x0000000100620000, event_ids=0x00000001001ff000) + 1649 at fsevent.rs:197
    frame #3: 0x000000010002d6dd rsnotify-repro`fsevent::callback::hf1094fd0c5c09dbeeia + 61
    frame #4: 0x00007fff92498ba1 FSEvents`implementation_callback_rpc + 2123
    frame #5: 0x00007fff92496672 FSEvents`_Xcallback_rpc + 254
    frame #6: 0x00007fff92496746 FSEvents`FSEventsD2F_server + 54
    frame #7: 0x00007fff9249bf75 FSEvents`FSEventsClientProcessMessageCallback + 44
    frame #8: 0x00007fff88de8d87 CoreFoundation`__CFMachPortPerform + 247
    frame #9: 0x00007fff88de8c79 CoreFoundation`__CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 41
    frame #10: 0x00007fff88de8beb CoreFoundation`__CFRunLoopDoSource1 + 475
    frame #11: 0x00007fff88dda767 CoreFoundation`__CFRunLoopRun + 2375
    frame #12: 0x00007fff88dd9bd8 CoreFoundation`CFRunLoopRunSpecific + 296
    frame #13: 0x00007fff88e91671 CoreFoundation`CFRunLoopRun + 97
    frame #14: 0x000000010003008a rsnotify-repro`fnfn + 410 at fsevent.rs:158
    frame #15: 0x000000010002feb9 rsnotify-repro`notify::boxed::F.FnBox<A>::call_box(self=0x0000000101437030, args=<unavailable>) + 89 at boxed.rs:516
    frame #16: 0x000000010002faac rsnotify-repro`notify::boxed::Box<FnBox<A, Output = R>+ Send + 'a>.FnOnce<A>::call_once(self=Box<FnBox<()>> at 0x0000000103a00bc0, args=<unavailable>) + 60 at boxed.rs:532
    frame #17: 0x000000010002f67e rsnotify-repro`fnfn + 78 at mod.rs:281
    frame #18: 0x000000010002f62a rsnotify-repro`notify::sys_common::unwind::try::try_fn<closure>(opt_closure=0x0000000103a00cf0) + 58 at mod.rs:156
    frame #19: 0x000000010003efc9 rsnotify-repro`__rust_try + 9
    frame #20: 0x000000010003d0ef rsnotify-repro`sys_common::unwind::try::inner_try::h9c69b1952218bc71tRr + 111
    frame #21: 0x000000010002f594 rsnotify-repro`notify::sys_common::unwind::try<closure>(f=closure at 0x0000000103a00d08) + 100 at mod.rs:126
    frame #22: 0x000000010002f40c rsnotify-repro`fnfn + 412 at mod.rs:281
    frame #23: 0x000000010002fcdd rsnotify-repro`notify::boxed::F.FnBox<A>::call_box(self=0x000000010143b000, args=<unavailable>) + 77 at boxed.rs:516
    frame #24: 0x000000010004040e rsnotify-repro`sys::thread::_$LT$impl$GT$::new::thread_start::h08e832c9db3841f0Qcw + 142
    frame #25: 0x00007fff8aba805a libsystem_pthread.dylib`_pthread_body + 131
    frame #26: 0x00007fff8aba7fd7 libsystem_pthread.dylib`_pthread_start + 176
    frame #27: 0x00007fff8aba53ed libsystem_pthread.dylib`thread_start + 13

[octplane]

Looks like the rsnotify wrapping around FSEvent has a bug, cf rust-lang/rust#29201 (comment)

@passcod , I'm not much familiar with the overall architecture of this piece of code. Are you? This is likely to change some of the rsnotify internals a bit..

[TyOverby]

I've updated the title.

[passcod]

For ref: https://github.com/passcod/rsnotify/blob/master/src/fsevent.rs#L132-L164

I didn't write this code, actually, and I'm not quite sure what it does, or why such a large unsafe block is needed. If we remove the unsafe and try to compile, can we shrink down the unsafe zone to the bare minimum? That won't make the bug disappear, but it should help coral down a bit.

What kind of internal reshuffle are you envisioning?

[andelf]

:( it was writed by me. @passcod

[andelf]

My bad. PRed, waiting for review.

Diagnose:

frame #2: 0x00000001000333b1 rsnotify-repronotify::fsevent::callback(stream_ref=0x0000000100500c50, info=0x00007fff5fbff8d0, num_events=1, event_paths=0x0000000100700140, event_flags=0x0000000100620000, event_ids=0x00000001001ff000) + 1649 at fsevent.rs:197`

Here, the info parameter is a stack address(in fn watch()). :(