Font cache thread intermittently cannot be reached during shutdown ("Couldn't receive FontCacheThread reply")

[jdm]

  ▶ TIMEOUT [expected PASS] /css/css-backgrounds/background-clip-color.html
  │ 
  │ VMware, Inc.
  │ softpipe
  │ 3.3 (Core Profile) Mesa 18.1.0-devel
  │ Shutting down the Constellation after generating an output file or exit flag specified
  │ VMware, Inc.
  │ softpipe
  │ 3.3 (Core Profile) Mesa 18.1.0-devel
  │ Shutting down the Constellation after generating an output file or exit flag specified
  │ Couldn't receive FontCacheThread reply: Io(Os { code: 104, kind: ConnectionReset, message: "Connection reset by peer" }) (thread Constellation, at libcore/result.rs:945)
  │ stack backtrace:
  │    0:     0x7f4fde5e6f6c - backtrace::backtrace::trace::h342f5d76ca5ceb8f
  │    1:     0x7f4fde5e6332 - backtrace::capture::Backtrace::new::hb9e84455e6bd3454
  │    2:     0x7f4fdb5746cc - servo::main::{{closure}}::h674a7c2a7ee03aeb
  │    3:     0x7f4fde608029 - std::panicking::rust_panic_with_hook::hfd6818535490a12f
  │                         at libstd/panicking.rs:401
  │    4:     0x7f4fde607e31 - std::panicking::begin_panic_fmt::hb49e0372029a7978
  │                         at libstd/panicking.rs:347
  │    5:     0x7f4fde607d82 - rust_begin_unwind
  │                         at libstd/panicking.rs:323
  │    6:     0x7f4fde62cbb0 - core::panicking::panic_fmt::he07a59762014a101
  │                         at libcore/panicking.rs:71
  │    7:     0x7f4fdcf6335d - core::result::unwrap_failed::h8b276bc62ba80418
  │    8:     0x7f4fdcf78110 - gfx::font_cache_thread::FontCacheThread::exit::h532c7134aad2ec25
  │    9:     0x7f4fdb661440 - <constellation::constellation::Constellation<Message, LTF, STF>>::run::h74f6f54e19bf70f4
  │   10:     0x7f4fdb5a6745 - std::sys_common::backtrace::__rust_begin_short_backtrace::h2054ee2241a5c9e6
  │   11:     0x7f4fdb671145 - _ZN3std9panicking3try7do_call17he037034e1b3683deE.llvm.14518841231994953458
  │   12:     0x7f4fde61d4ee - __rust_maybe_catch_panic
  │                         at libpanic_unwind/lib.rs:101
  │   13:     0x7f4fdb6869e0 - <F as alloc::boxed::FnBox<A>>::call_box::h0c943eeb7dc9f976
  │   14:     0x7f4fde611ae7 - <alloc::boxed::Box<alloc::boxed::FnBox<A, Output$u3d$R$GT$$u20$$u2b$$u20$$u27$a$GT$$u20$as$u20$core..ops..function..FnOnce$LT$A$GT$$GT$::call_once::h9987f61f4f93afa5
  │                         at /checkout/src/liballoc/boxed.rs:645
  │                          - std::sys_common::thread::start_thread::h7a671b9cfa13995a
  │                         at libstd/sys_common/thread.rs:24
  │   15:     0x7f4fde5f9cc8 - std::sys::unix::thread::Thread::new::thread_start::had4c521b4cf0110f
  │                         at libstd/sys/unix/thread.rs:90
  │   16:     0x7f4fda462183 - start_thread
  │   17:     0x7f4fd8d2903c - clone
  │   18:                0x0 - <unknown>
  └ ERROR 2018-05-18T22:14:49Z: servo: Couldn't receive FontCacheThread reply: Io(Os { code: 104, kind: ConnectionReset, message: "Connection reset by peer" })

[jdm]

  ▶ TIMEOUT [expected FAIL] /css/CSS2/positioning/absolute-replaced-width-039.xht
  │ 
  │ VMware, Inc.
  │ softpipe
  │ 3.3 (Core Profile) Mesa 18.1.0-devel
  │ Shutting down the Constellation after generating an output file or exit flag specified
  │ Couldn't receive FontCacheThread reply: Io(Custom { kind: ConnectionReset, error: StringError("All senders for this socket closed") }) (thread Constellation, at libcore/result.rs:1009)
  │ stack backtrace:
  │    0:     0x7f4b96f8d1cc - backtrace::backtrace::trace::h34a5004b5e0f1dc7
  │    1:     0x7f4b96f8c462 - <backtrace::capture::Backtrace as core::default::Default>::default::hae829d87a5db9150
  │    2:     0x7f4b96f8c4d8 - backtrace::capture::Backtrace::new::hcbbf9ea3df342ffc
  │    3:     0x7f4b93f6d559 - servo::main::{{closure}}::h48341614c6b12575
  │    4:     0x7f4b96fb8803 - std::panicking::rust_panic_with_hook::hd470ff3b3e7a1b18
  │                         at libstd/panicking.rs:480
  │    5:     0x7f4b96fb8369 - std::panicking::continue_panic_fmt::hf0cf39ae1e114602
  │                         at libstd/panicking.rs:390
  │    6:     0x7f4b96fb8265 - rust_begin_unwind
  │                         at libstd/panicking.rs:325
  │    7:     0x7f4b96fd946b - core::panicking::panic_fmt::hf53111ba26d35bb0
  │                         at libcore/panicking.rs:77
  │    8:     0x7f4b957a05dd - core::result::unwrap_failed::h13382972dbfeaa5a
  │    9:     0x7f4b95791c40 - gfx::font_cache_thread::FontCacheThread::exit::hc107876625d209bc
  │   10:     0x7f4b9402cfa9 - <constellation::constellation::Constellation<Message, LTF, STF>>::run::h0ad40e6924e1bf31
  │   11:     0x7f4b93f7aede - std::sys_common::backtrace::__rust_begin_short_backtrace::hf92973145e9bcb30
  │   12:     0x7f4b93fd9235 - std::panicking::try::do_call::hf2d22820ac1bc7b4
  │   13:     0x7f4b96fca679 - __rust_maybe_catch_panic
  │                         at libpanic_unwind/lib.rs:102
  │   14:     0x7f4b93fde6e0 - <F as alloc::boxed::FnBox<A>>::call_box::h5d2447df2765b5a8
  │   15:     0x7f4b96fb575a - <alloc::boxed::Box<(dyn alloc::boxed::FnBox<A, Output$u3d$R$GT$$u20$$u2b$$u20$$u27$a$RP$$GT$$u20$as$u20$core..ops..function..FnOnce$LT$A$GT$$GT$::call_once::h9d1cd498499ed135
  │                         at liballoc/boxed.rs:682
  │                          - std::sys_common::thread::start_thread::ha4bfe77455e6e434
  │                         at libstd/sys_common/thread.rs:24
  │   16:     0x7f4b96fa2ce5 - std::sys::unix::thread::Thread::new::thread_start::hebe133da3ea5230a
  │                         at libstd/sys/unix/thread.rs:90
  │   17:     0x7f4b9227b183 - start_thread
  │   18:     0x7f4b9050703c - clone
  │   19:                0x0 - <unknown>
  └ ERROR 2018-10-12T17:59:45Z: servo: Couldn't receive FontCacheThread reply: Io(Custom { kind: ConnectionReset, error: StringError("All senders for this socket closed") })

[CYBAI]

  ▶ TIMEOUT [expected FAIL] /css/CSS2/linebox/vertical-align-baseline-008.xht
  │ 
  │ error: XDG_RUNTIME_DIR not set in the environment.
  │ libEGL warning: No hardware driver found, falling back to software rendering
  │ Shutting down the Constellation after generating an output file or exit flag specified
  │ Couldn't receive FontCacheThread reply: Disconnected (thread Constellation, at components/gfx/font_cache_thread.rs:496)
  │    0: servo::backtrace::print
  │    1: servo::main::{{closure}}
  │    2: std::panicking::rust_panic_with_hook
  │              at src/libstd/panicking.rs:515
  │    3: rust_begin_unwind
  │              at src/libstd/panicking.rs:419
  │    4: core::panicking::panic_fmt
  │              at src/libcore/panicking.rs:111
  │    5: core::option::expect_none_failed
  │              at src/libcore/option.rs:1268
  │    6: gfx::font_cache_thread::FontCacheThread::exit
  │    7: constellation::constellation::Constellation<Message,LTF,STF,SWF>::run
  │    8: std::sys_common::backtrace::__rust_begin_short_backtrace
  │    9: core::ops::function::FnOnce::call_once{{vtable.shim}}
  │   10: <alloc::boxed::Box<F> as core::ops::function::FnOnce<A>>::call_once
  │              at /rustc/42abbd8878d3b67238f3611b0587c704ba94f39c/src/liballoc/boxed.rs:1008
  │   11: <alloc::boxed::Box<F> as core::ops::function::FnOnce<A>>::call_once
  │              at /rustc/42abbd8878d3b67238f3611b0587c704ba94f39c/src/liballoc/boxed.rs:1008
  │       std::sys::unix::thread::Thread::new::thread_start
  │              at src/libstd/sys/unix/thread.rs:87
  │   12: start_thread
  │   13: __clone
  └ [2020-04-26T04:43:06Z ERROR servo] Couldn't receive FontCacheThread reply: Disconnected

[CYBAI]

  ▶ TIMEOUT [expected FAIL] /css/CSS2/selectors/first-letter-punctuation-044.xht
  │ 
  │ error: XDG_RUNTIME_DIR not set in the environment.
  │ libEGL warning: No hardware driver found, falling back to software rendering
  │ Shutting down the Constellation after generating an output file or exit flag specified
  │ Couldn't receive FontCacheThread reply: Disconnected (thread Constellation, at components/gfx/font_cache_thread.rs:496)
  │    0: servo::backtrace::print
  │    1: servo::main::{{closure}}
  │    2: std::panicking::rust_panic_with_hook
  │              at src/libstd/panicking.rs:515
  │    3: rust_begin_unwind
  │              at src/libstd/panicking.rs:419
  │    4: core::panicking::panic_fmt
  │              at src/libcore/panicking.rs:111
  │    5: core::option::expect_none_failed
  │              at src/libcore/option.rs:1268
  │    6: gfx::font_cache_thread::FontCacheThread::exit
  │    7: constellation::constellation::Constellation<Message,LTF,STF,SWF>::run
  │    8: std::sys_common::backtrace::__rust_begin_short_backtrace
  │    9: core::ops::function::FnOnce::call_once{{vtable.shim}}
  │   10: <alloc::boxed::Box<F> as core::ops::function::FnOnce<A>>::call_once
  │              at /rustc/42abbd8878d3b67238f3611b0587c704ba94f39c/src/liballoc/boxed.rs:1008
  │   11: <alloc::boxed::Box<F> as core::ops::function::FnOnce<A>>::call_once
  │              at /rustc/42abbd8878d3b67238f3611b0587c704ba94f39c/src/liballoc/boxed.rs:1008
  │       std::sys::unix::thread::Thread::new::thread_start
  │              at src/libstd/sys/unix/thread.rs:87
  │   12: start_thread
  │   13: __clone
  └ [2020-04-27T11:50:46Z ERROR servo] Couldn't receive FontCacheThread reply: Disconnected

[jdm]

Since this can affect any test and the backtraces always look the same, I don't think we get a lot of value from sharing new instances of this failure.

[CYBAI]

Indeed. I will refer this issue directly then! Thanks for the notice!