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Segfault when run from child thread.

See original GitHub issue

Hello! Thank you for building this, first of all! I’ve had alright success running this from the main thread, but it seems to die when run from a child. Here’s the segfault:

1   0x7fdcc656c247 /usr/lib/x86_64-linux-gnu/ [0x7fdcc656c247]
2   0x7fdcc7ced999 /usr/lib/x86_64-linux-gnu/ [0x7fdcc7ced999]
3   0x7fdcc7d31d9a /usr/lib/x86_64-linux-gnu/ [0x7fdcc7d31d9a]
4   0x7fdcc7d32219 /usr/lib/x86_64-linux-gnu/ [0x7fdcc7d32219]
5   0x7fdcc7faf0d0 /usr/lib/x86_64-linux-gnu/ [0x7fdcc7faf0d0]
6   0x7fdcc6833e72 /usr/lib/x86_64-linux-gnu/ [0x7fdcc6833e72]
7   0x7fdcc48f0041 /lib/x86_64-linux-gnu/ [0x7fdcc48f0041]
8   0x7fdcc48f013a /lib/x86_64-linux-gnu/ [0x7fdcc48f013a]
9   0x7fdcc48ceb9e /lib/x86_64-linux-gnu/ [0x7fdcc48ceb9e]
10  0x55777992389a target/debug/rust_ksl_uploader(+0x889a) [0x55777992389a]
Segmentation fault (core dumped)

And here’s the minimal code to reproduce:

extern crate web_view;

use web_view::*;
use std::thread::spawn;

const INDEX: &str = r#"<!DOCTYPE html>
<html lang="en" dir="ltr">
    <meta charset="utf-8">
    This is a test.

fn main() {
    let size = (800, 800);
    let resizable = true;
    let debug = true;
    let init_cb = |_webview| {};
    let frontend_cb = |_webview: &mut _, _arg: &_, _userdata: &mut _| {};
    let userdata = ();
    let view = spawn(move || {
        run("test thread", Content::Html(INDEX), Some(size), resizable, debug, init_cb, frontend_cb, userdata);

    view.join().expect("Join Error");

Issue Analytics

  • State:open
  • Created 5 years ago
  • Comments:7

github_iconTop GitHub Comments

Zenniicommented, Jun 25, 2019

I’ve come across this issue as well. Ubuntu 18.04 and libwebkit2gtk-4.0 package is installed (If that’s even necessary or useful). Here is the minimal code that consistently produces the issue for me with the current API (With sleep to show the window hangs):

use web_view::*;
use std::time::Duration;

fn main() {
    std::thread::spawn(|| {
        let mut wv = web_view::builder()
            .invoke_handler(|wv, arg| {
                // terminate in here causes free(): invalid pointer
            .build().expect("Build Error");"Run Error");

I did some of my own snooping around by running it through valgrind and found that when I placed mem::forget(_lock); near the bottom of the _into_inner(&mut self) function in a local copy of the crate, a ton of errors reported by valgrind go away during the drop and malloc_consolidate(): invalid chunk size stops happening and thus the program doesn’t crash, but the window will hang until the main thread is done and the entire program still closes with signal 6 SIGABRT when it’s done. You can circumvent the hanging by waiting an indeterminate amount of time after the window thinks it’s dead and returns None to step a few times, like this:

std::thread::spawn(|| {
    let mut wv = web_view::builder()
        .invoke_handler(|wv, arg| {Ok(())})
    let mut looped = 0;
    loop {
        match wv.step() {
            Some(Ok(a)) => (),
            Some(Err(e)) => (),
            None => {
                looped += 1;
                if looped > 4 {

but it’s a very ugly magical workaround and I’m really unsure as to why it works exactly. It feels like some kind of race condition, but I’m not sure how the window manager works. Hope this helps deduce what’s wrong.

quadrupleslapcommented, Jan 30, 2019

Note: You could never run this on a non-main thread on macOS anyway, because macOS is weird like that.

Read more comments on GitHub >

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