Prevent panic on layout send in finish-load

[gterzian]

Do not run the finish load steps if the pipeline has been discarded by the time the parser finishes.

---

• ./mach build -d does not report any errors
• ./mach test-tidy does not report any errors
• These changes fix #22955 (GitHub issue number if applicable)

• There are tests for these changes OR
• These changes do not require tests because ___

[highfive]

Heads up! This PR modifies the following files:

• @asajeffrey: components/script/script_thread.rs
• @KiChjang: components/script/script_thread.rs

[highfive]

Warning

• These commits modify script code, but no tests are modified. Please consider adding a test!

[gterzian]

@bors-servo try=wpt

@jdm I think this one might actually fix #22955 (and hopefully not break other things)

[bors-servo]

⌛ Trying commit bc9c4d8 with merge 4902566...

[jdm]

I think a more robust fix would be calling ServoParser::abort on Document::current_parser (if it exists) when we know a pipeline is being closed.

[gterzian]

@jdm Thanks, I have changed the fix accordingly.

[jdm]

@bors-servo try=wpt

[bors-servo]

⌛ Testing commit 1fab241 with merge d92d0c6...

[bors-servo]

💔 Test failed - status-taskcluster

[jdm]

Sorry, the try build for #24821 stomped on the branch so all the test runners couldn't clone the appropriate git revision. I'm going to wait until the tests for #24821 start running to retry this.

[jdm]

@bors-servo retry

[jdm]

@bors-servo try=wpt

[bors-servo]

⌛ Trying commit 1fab241 with merge 7afe06d...

[bors-servo]

💔 Test failed - status-taskcluster

[gterzian]

0 matches
{
    "status": "CRASH", 
    "group": "default", 
    "message": null, 
    "stack": null, 
    "subtest": null, 
    "test": "/html/webappapis/dynamic-markup-insertion/opening-the-input-stream/url.window.html", 
    "line": 65380, 
    "action": "test_result", 
    "expected": "OK"
}
{
    "status": "CRASH", 
    "group": "default", 
    "message": null, 
    "stack": null, 
    "subtest": null, 
    "test": "/html/webappapis/dynamic-markup-insertion/opening-the-input-stream/abort-refresh-immediate.window.html", 
    "line": 65933, 
    "action": "test_result", 
    "expected": "TIMEOUT"
}
{
    "status": "CRASH", 
    "group": "default", 
    "message": null, 
    "stack": null, 
    "subtest": null, 
    "test": "/html/webappapis/dynamic-markup-insertion/opening-the-input-stream/tasks.window.html", 
    "line": 66212, 
    "action": "test_result", 
    "expected": "TIMEOUT"
}

  │    7: <html5ever::tree_builder::TreeBuilder<Handle,Sink> as html5ever::tokenizer::interface::TokenSink>::process_token
  │    8: _ZN9html5ever9tokenizer21Tokenizer$LT$Sink$GT$13process_token17hdf12db064f2abc2dE.llvm.14290903763764066736
  │    9: html5ever::tokenizer::Tokenizer<Sink>::end
  │   10: script::dom::servoparser::ServoParser::abort
  │   11: script::script_thread::ScriptThread::handle_exit_pipeline_msg
  │   12: script::script_thread::ScriptThread::handle_msg_from_constellation
  │   13: _ZN6script13script_thread12ScriptThread11handle_msgs17h702aaab883c81f98E.llvm.14290903763764066736
  │   14: script::script_thread::ScriptThread::start
  │   15: profile_traits::mem::ProfilerChan::run_with_memory_reporting
  │   16: std::sys_common::backtrace::__rust_begin_short_backtrace
  │   17: _ZN3std9panicking3try7do_call17h0956d3ff2ca15edbE.llvm.2944147132392252601
  │   18: __rust_maybe_catch_panic
  │              at src/libpanic_unwind/lib.rs:81
  │   19: core::ops::function::FnOnce::call_once{{vtable.shim}}
  │   20: <alloc::boxed::Box<F> as core::ops::function::FnOnce<A>>::call_once
  │              at /rustc/1bd30ce2aac40c7698aa4a1b9520aa649ff2d1c5/src/liballoc/boxed.rs:942
  │   21: <alloc::boxed::Box<F> as core::ops::function::FnOnce<A>>::call_once
  │              at /rustc/1bd30ce2aac40c7698aa4a1b9520aa649ff2d1c5/src/liballoc/boxed.rs:942
  │       std::sys_common::thread::start_thread
  │              at src/libstd/sys_common/thread.rs:13
  │       std::sys::unix::thread::Thread::new::thread_start
  │              at src/libstd/sys/unix/thread.rs:79
  │   22: start_thread
  │   23: __clone
  │ 
  │ [2019-11-22T05:35:06Z ERROR servo] called `Result::unwrap()` on an `Err` value: "SendError(..)"
  └ Pipeline failed in hard-fail mode.  Crashing!

Looks like aborting the parser when the pipeline exits results in other crashes.

[jdm]

The async parser doesn't get used unless dom.servoparser.async_html_tokenizer.enabled is true. I think we want to abort the parser before we start tearing down the window to avoid this.

[jdm]

In particular, because aborting the parser can cause additional parser activity, I think we need to do that before we shut down the layout thread.

[gterzian]

@bors-servo try=wpt

Ok, trying before shutting down layout...

[bors-servo]

⌛ Trying commit f28ffac with merge 1b707ee...

[bors-servo]

☀️ Test successful - linux-rel-css, linux-rel-wpt, status-taskcluster
State: approved= try=True

[jdm]

@bors-servo r+

[bors-servo]

📌 Commit f28ffac has been approved by jdm

[bors-servo]

⌛ Testing commit f28ffac with merge 1b524ea...

[bors-servo]

☀️ Test successful - linux-rel-css, linux-rel-wpt, status-taskcluster
Approved by: jdm
Pushing 1b524ea to master...