feat: shorten thread names

The Linux kernel imposes a 15-byte limit on thread names[1]. This means
information that does not fit in this limit, e.g., the pipeline ID of
layout and script threads, is lost in a debugger and profiler (see the
first column of the table below).

This commit shortens the thread names used in Servo to maximize the
amount of information conveyed. It also rectifies some inconsistencies
in the names.

|       Before      |       After       |
|-------------------|-------------------|
| `BluetoothThread` | `Bluetooth`       |
| `CanvasThread`    | `Canvas`          |
| `display alert d` | `AlertDialog`     |
| `FontCacheThread` | `FontCache`       |
| `GLPlayerThread`  | `GLPlayer`        |
| `HTML Parser`     | `Parse:www.examp` |
| `LayoutThread Pi` | `Layout(1,1)`     |
| `Memory profiler` | `MemoryProfiler`  |
| `Memory profiler` | `MemoryProfTimer` |
| `OfflineAudioCon` | `OfflineACResolv` |
| `PullTimelineMar` | `PullTimelineDat` |
| `ScriptThread Pi` | `Script(1,1)`     |
| `WebWorker for h` | `WW:www.example.` |
| `ServiceWorker f` | `SW:www.example.` |
| `ServiceWorkerMa` | `SvcWorkerManage` |
| `Time profiler t` | `TimeProfTimer`   |
| `Time profiler`   | `TimeProfiler`    |
| `WebGL thread`    | `WebGL`           |
| `Choose a device` | `DevicePicker`    |
| `Pick a file`     | `FilePicker`      |
| `Pick files`      | `FilePicker`      |

[1]: https://stackoverflow.com/questions/5026531/thread-name-longer-than-15-chars

21 files changed, 59 insertions, 29 deletions

diff --git a/components/bluetooth/lib.rs b/components/bluetooth/lib.rs
index cb6a2587c67..9a48d19eec9 100644
--- a/components/bluetooth/lib.rs
+++ b/components/bluetooth/lib.rs
@@ -71,7 +71,7 @@ impl BluetoothThreadFactory for IpcSender<BluetoothRequest> {
         }
         .ok();
         thread::Builder::new()
-            .name("BluetoothThread".to_owned())
+            .name("Bluetooth".to_owned())
             .spawn(move || {
                 BluetoothManager::new(receiver, adapter, embedder_proxy).start();
             })
diff --git a/components/canvas/canvas_paint_thread.rs b/components/canvas/canvas_paint_thread.rs
index b426d398a72..f7c1d38b76f 100644
--- a/components/canvas/canvas_paint_thread.rs
+++ b/components/canvas/canvas_paint_thread.rs
@@ -62,7 +62,7 @@ impl<'a> CanvasPaintThread<'a> {
         let msg_receiver = ROUTER.route_ipc_receiver_to_new_crossbeam_receiver(ipc_receiver);
         let (create_sender, create_receiver) = unbounded();
         thread::Builder::new()
-            .name("CanvasThread".to_owned())
+            .name("Canvas".to_owned())
             .spawn(move || {
                 let mut canvas_paint_thread = CanvasPaintThread::new(webrender_api, font_cache_thread);
                 loop {
diff --git a/components/canvas/webgl_thread.rs b/components/canvas/webgl_thread.rs
index 1f2cc832007..423d799e27f 100644
--- a/components/canvas/webgl_thread.rs
+++ b/components/canvas/webgl_thread.rs
@@ -312,7 +312,7 @@ impl WebGLThread {
     /// in parallel on its own dedicated thread.
     pub(crate) fn run_on_own_thread(init: WebGLThreadInit) {
         thread::Builder::new()
-            .name("WebGL thread".to_owned())
+            .name("WebGL".to_owned())
             .spawn(move || {
                 let mut data = WebGLThread::new(init);
                 data.process();
diff --git a/components/devtools/actors/timeline.rs b/components/devtools/actors/timeline.rs
index b21990ae0b0..f200b67c382 100644
--- a/components/devtools/actors/timeline.rs
+++ b/components/devtools/actors/timeline.rs
@@ -158,7 +158,7 @@ impl TimelineActor {
         }
 
         thread::Builder::new()
-            .name("PullTimelineMarkers".to_owned())
+            .name("PullTimelineData".to_owned())
             .spawn(move || loop {
                 if !*is_recording.lock().unwrap() {
                     break;
diff --git a/components/devtools/lib.rs b/components/devtools/lib.rs
index 28c6675da42..4b675191c8b 100644
--- a/components/devtools/lib.rs
+++ b/components/devtools/lib.rs
@@ -573,7 +573,7 @@ fn run_server(
     }
 
     thread::Builder::new()
-        .name("DevtoolsClientAcceptor".to_owned())
+        .name("DevtCliAcceptor".to_owned())
         .spawn(move || {
             // accept connections and process them, spawning a new thread for each one
             for stream in listener.incoming() {
diff --git a/components/gfx/font_cache_thread.rs b/components/gfx/font_cache_thread.rs
index 866d3c68cfd..b457867bc5b 100644
--- a/components/gfx/font_cache_thread.rs
+++ b/components/gfx/font_cache_thread.rs
@@ -444,7 +444,7 @@ impl FontCacheThread {
 
         let channel_to_self = chan.clone();
         thread::Builder::new()
-            .name("FontCacheThread".to_owned())
+            .name("FontCache".to_owned())
             .spawn(move || {
                 // TODO: Allow users to specify these.
                 let generic_fonts = populate_generic_fonts();
diff --git a/components/layout_thread/lib.rs b/components/layout_thread/lib.rs
index ba2a1f27f68..79d84526b48 100644
--- a/components/layout_thread/lib.rs
+++ b/components/layout_thread/lib.rs
@@ -285,7 +285,7 @@ impl LayoutThreadFactory for LayoutThread {
         dump_flow_tree: bool,
     ) {
         thread::Builder::new()
-            .name(format!("LayoutThread {:?}", id))
+            .name(format!("Layout{}", id))
             .spawn(move || {
                 thread_state::initialize(ThreadState::LAYOUT);
 
diff --git a/components/layout_thread_2020/lib.rs b/components/layout_thread_2020/lib.rs
index 60aa8c7b0c1..ef99a27668f 100644
--- a/components/layout_thread_2020/lib.rs
+++ b/components/layout_thread_2020/lib.rs
@@ -253,7 +253,7 @@ impl LayoutThreadFactory for LayoutThread {
         dump_flow_tree: bool,
     ) {
         thread::Builder::new()
-            .name(format!("LayoutThread {:?}", id))
+            .name(format!("Layout{}", id))
             .spawn(move || {
                 thread_state::initialize(ThreadState::LAYOUT);
 
diff --git a/components/media/media_thread.rs b/components/media/media_thread.rs
index 9dc3bf625f1..41bbaa6e99f 100644
--- a/components/media/media_thread.rs
+++ b/components/media/media_thread.rs
@@ -34,7 +34,7 @@ impl GLPlayerThread {
     ) -> GLPlayerSender<GLPlayerMsg> {
         let (sender, receiver) = glplayer_channel::<GLPlayerMsg>().unwrap();
         thread::Builder::new()
-            .name("GLPlayerThread".to_owned())
+            .name("GLPlayer".to_owned())
             .spawn(move || {
                 let mut renderer = GLPlayerThread::new(external_images);
                 loop {
diff --git a/components/profile/mem.rs b/components/profile/mem.rs
index 44956176e8a..45460ec6c90 100644
--- a/components/profile/mem.rs
+++ b/components/profile/mem.rs
@@ -37,7 +37,7 @@ impl Profiler {
         if let Some(period) = period {
             let chan = chan.clone();
             thread::Builder::new()
-                .name("Memory profiler timer".to_owned())
+                .name("MemoryProfTimer".to_owned())
                 .spawn(move || loop {
                     thread::sleep(duration_from_seconds(period));
                     if chan.send(ProfilerMsg::Print).is_err() {
@@ -50,7 +50,7 @@ impl Profiler {
         // Always spawn the memory profiler. If there is no timer thread it won't receive regular
         // `Print` events, but it will still receive the other events.
         thread::Builder::new()
-            .name("Memory profiler".to_owned())
+            .name("MemoryProfiler".to_owned())
             .spawn(move || {
                 let mut mem_profiler = Profiler::new(port);
                 mem_profiler.start();
diff --git a/components/profile/time.rs b/components/profile/time.rs
index 3254bfe017c..68fe11e4d13 100644
--- a/components/profile/time.rs
+++ b/components/profile/time.rs
@@ -174,7 +174,7 @@ impl Profiler {
                 // Spawn the time profiler thread
                 let outputoption = option.clone();
                 thread::Builder::new()
-                    .name("Time profiler".to_owned())
+                    .name("TimeProfiler".to_owned())
                     .spawn(move || {
                         let trace = file_path.as_ref().and_then(|p| TraceDump::new(p).ok());
                         let mut profiler = Profiler::new(port, trace, Some(outputoption));
@@ -188,7 +188,7 @@ impl Profiler {
                         // Spawn a timer thread
                         let chan = chan.clone();
                         thread::Builder::new()
-                            .name("Time profiler timer".to_owned())
+                            .name("TimeProfTimer".to_owned())
                             .spawn(move || loop {
                                 thread::sleep(duration_from_seconds(period));
                                 if chan.send(ProfilerMsg::Print).is_err() {
@@ -204,7 +204,7 @@ impl Profiler {
                 if file_path.is_some() {
                     // Spawn the time profiler
                     thread::Builder::new()
-                        .name("Time profiler".to_owned())
+                        .name("TimeProfiler".to_owned())
                         .spawn(move || {
                             let trace = file_path.as_ref().and_then(|p| TraceDump::new(p).ok());
                             let mut profiler = Profiler::new(port, trace, None);
@@ -214,7 +214,7 @@ impl Profiler {
                 } else {
                     // No-op to handle messages when the time profiler is not printing:
                     thread::Builder::new()
-                        .name("Time profiler".to_owned())
+                        .name("TimeProfiler".to_owned())
                         .spawn(move || loop {
                             match port.recv() {
                                 Err(_) => break,
diff --git a/components/script/dom/dedicatedworkerglobalscope.rs b/components/script/dom/dedicatedworkerglobalscope.rs
index a638ce85257..6d1792f87c2 100644
--- a/components/script/dom/dedicatedworkerglobalscope.rs
+++ b/components/script/dom/dedicatedworkerglobalscope.rs
@@ -328,7 +328,6 @@ impl DedicatedWorkerGlobalScope {
         context_sender: Sender<ContextForRequestInterrupt>,
     ) -> JoinHandle<()> {
         let serialized_worker_url = worker_url.to_string();
-        let name = format!("WebWorker for {}", serialized_worker_url);
         let top_level_browsing_context_id = TopLevelBrowsingContextId::installed();
         let current_global = GlobalScope::current().expect("No current global object");
         let origin = current_global.origin().immutable().clone();
@@ -337,7 +336,7 @@ impl DedicatedWorkerGlobalScope {
         let current_global_https_state = current_global.get_https_state();
 
         thread::Builder::new()
-            .name(name)
+            .name(format!("WW:{}", worker_url.debug_compact()))
             .spawn(move || {
                 thread_state::initialize(ThreadState::SCRIPT | ThreadState::IN_WORKER);
 
diff --git a/components/script/dom/offlineaudiocontext.rs b/components/script/dom/offlineaudiocontext.rs
index bbdf9e1a79f..878bdedd314 100644
--- a/components/script/dom/offlineaudiocontext.rs
+++ b/components/script/dom/offlineaudiocontext.rs
@@ -153,7 +153,7 @@ impl OfflineAudioContextMethods for OfflineAudioContext {
             .task_manager()
             .dom_manipulation_task_source_with_canceller();
         Builder::new()
-            .name("OfflineAudioContextResolver".to_owned())
+            .name("OfflineACResolver".to_owned())
             .spawn(move || {
                 let _ = receiver.recv();
                 let _ = task_source.queue_with_canceller(
diff --git a/components/script/dom/serviceworkerglobalscope.rs b/components/script/dom/serviceworkerglobalscope.rs
index 911c635e38d..934b9b88b3a 100644
--- a/components/script/dom/serviceworkerglobalscope.rs
+++ b/components/script/dom/serviceworkerglobalscope.rs
@@ -302,7 +302,7 @@ impl ServiceWorkerGlobalScope {
         let serialized_worker_url = script_url.to_string();
         let origin = scope_url.origin();
         thread::Builder::new()
-            .name(format!("ServiceWorker for {}", serialized_worker_url))
+            .name(format!("SW:{}", script_url.debug_compact()))
             .spawn(move || {
                 thread_state::initialize(ThreadState::SCRIPT | ThreadState::IN_WORKER);
                 let runtime = new_rt_and_cx(None);
diff --git a/components/script/dom/servoparser/async_html.rs b/components/script/dom/servoparser/async_html.rs
index 8b0a156842d..538007d9057 100644
--- a/components/script/dom/servoparser/async_html.rs
+++ b/components/script/dom/servoparser/async_html.rs
@@ -256,7 +256,7 @@ impl Tokenizer {
         // will be generated from the input provided. These parser actions are then passed
         // onto the main thread to be executed.
         thread::Builder::new()
-            .name(String::from("HTML Parser"))
+            .name(format!("Parse:{}", tokenizer.url.debug_compact()))
             .spawn(move || {
                 run(
                     sink,
diff --git a/components/script/script_thread.rs b/components/script/script_thread.rs
index 1b28c337d56..8b3ba539809 100644
--- a/components/script/script_thread.rs
+++ b/components/script/script_thread.rs
@@ -773,7 +773,7 @@ impl ScriptThreadFactory for ScriptThread {
         let (sender, receiver) = unbounded();
         let layout_chan = sender.clone();
         thread::Builder::new()
-            .name(format!("ScriptThread {:?}", state.id))
+            .name(format!("Script{}", state.id))
             .spawn(move || {
                 thread_state::initialize(ThreadState::SCRIPT);
                 PipelineNamespace::install(state.pipeline_namespace_id);
diff --git a/components/script/serviceworker_manager.rs b/components/script/serviceworker_manager.rs
index 46cf22531c8..e3db04c4235 100644
--- a/components/script/serviceworker_manager.rs
+++ b/components/script/serviceworker_manager.rs
@@ -499,7 +499,7 @@ impl ServiceWorkerManagerFactory for ServiceWorkerManager {
         let resource_port = ROUTER.route_ipc_receiver_to_new_crossbeam_receiver(resource_port);
         let _ = resource_sender.send(CoreResourceMsg::NetworkMediator(resource_chan, origin));
         if thread::Builder::new()
-            .name("ServiceWorkerManager".to_owned())
+            .name("SvcWorkerManager".to_owned())
             .spawn(move || {
                 ServiceWorkerManager::new(
                     own_sender,
diff --git a/components/style/global_style_data.rs b/components/style/global_style_data.rs
index 872d97745f4..4e3d11b94b7 100644
--- a/components/style/global_style_data.rs
+++ b/components/style/global_style_data.rs
@@ -37,7 +37,7 @@ pub struct StyleThreadPool {
 }
 
 fn thread_name(index: usize) -> String {
-    format!("StyleThread#{}", index)
+    format!("Style#{}", index)
 }
 
 // A counter so that we can wait for shutdown of all threads. See
diff --git a/components/url/lib.rs b/components/url/lib.rs
index 944d02f29f7..a19159ef031 100644
--- a/components/url/lib.rs
+++ b/components/url/lib.rs
@@ -179,6 +179,39 @@ impl ServoUrl {
         Ok(Self::from_url(Url::from_file_path(path)?))
     }
 
+    /// Return a non-standard shortened form of the URL. Mainly intended to be
+    /// used for debug printing in a constrained space (e.g., thread names).
+    pub fn debug_compact(&self) -> impl std::fmt::Display + '_ {
+        match self.scheme() {
+            "http" | "https" => {
+                // Strip `scheme://`, which is hardly useful for identifying websites
+                let mut st = self.as_str();
+                st = st.strip_prefix(self.scheme()).unwrap_or(st);
+                st = st.strip_prefix(":").unwrap_or(st);
+                st = st.trim_start_matches('/');
+
+                // Don't want to return an empty string
+                if st.is_empty() {
+                    st = self.as_str();
+                }
+
+                st
+            },
+            "file" => {
+                // The only useful part in a `file` URL is usually only the last
+                // few components
+                let path = self.path();
+                let i = path.rfind('/');
+                let i = i.map(|i| path[..i].rfind('/').unwrap_or(i));
+                match i {
+                    None | Some(0) => path,
+                    Some(i) => &path[i + 1..],
+                }
+            },
+            _ => self.as_str(),
+        }
+    }
+
     /// <https://w3c.github.io/webappsec-secure-contexts/#potentially-trustworthy-url>
     pub fn is_potentially_trustworthy(&self) -> bool {
         // Step 1
diff --git a/components/webdriver_server/lib.rs b/components/webdriver_server/lib.rs
index b6582cfab5b..cd54d1a8c8f 100644
--- a/components/webdriver_server/lib.rs
+++ b/components/webdriver_server/lib.rs
@@ -109,7 +109,7 @@ fn cookie_msg_to_cookie(cookie: cookie::Cookie) -> Cookie {
 pub fn start_server(port: u16, constellation_chan: Sender<ConstellationMsg>) {
     let handler = Handler::new(constellation_chan);
     thread::Builder::new()
-        .name("WebdriverHttpServer".to_owned())
+        .name("WebDriverHttpServer".to_owned())
         .spawn(move || {
             let address = SocketAddrV4::new("0.0.0.0".parse().unwrap(), port);
             match server::start(SocketAddr::V4(address), handler, extension_routes()) {
diff --git a/ports/winit/browser.rs b/ports/winit/browser.rs
index 1098c0bbfbc..4c685fd4b57 100644
--- a/ports/winit/browser.rs
+++ b/ports/winit/browser.rs
@@ -307,7 +307,7 @@ where
                         }
                     } else {
                         thread::Builder::new()
-                            .name("display alert dialog".to_owned())
+                            .name("AlertDialog".to_owned())
                             .spawn(move || match definition {
                                 PromptDefinition::Alert(mut message, sender) => {
                                     if origin == PromptOrigin::Untrusted {
@@ -554,10 +554,8 @@ fn prompt_user(_prompt: PermissionPrompt) -> PermissionRequest {
 
 #[cfg(target_os = "linux")]
 fn platform_get_selected_devices(devices: Vec<String>) -> Option<String> {
-    let picker_name = "Choose a device";
-
     thread::Builder::new()
-        .name(picker_name.to_owned())
+        .name("DevicePicker".to_owned())
         .spawn(move || {
             let dialog_rows: Vec<&str> = devices.iter().map(|s| s.as_ref()).collect();
             let dialog_rows: Option<&[&str]> = Some(dialog_rows.as_slice());
@@ -592,7 +590,7 @@ fn get_selected_files(patterns: Vec<FilterPattern>, multiple_files: bool) -> Opt
         "Pick a file"
     };
     thread::Builder::new()
-        .name(picker_name.to_owned())
+        .name("FilePicker".to_owned())
         .spawn(move || {
             let mut filters = vec![];
             for p in patterns {