Shorten thread names exceeding the 15-char Linux pthread_setname_np limit

[Copilot]

Linux silently truncates thread names to 15 characters via pthread_setname_np, making several runtime threads indistinguishable in ps, top, htop, and debuggers.

Description

Renamed six thread names that exceeded the limit across all affected files, including the Mono browser WASM runtime:

Old Name	New Name
.NET Stack overflow trace logger (33)	.NET SO Tracer (14)
.NET Stack overflow create dump (32)	.NET SO Dumper (14)
.NET Tiered Compilation Worker (30)	.NET Tiered JIT (15)
.NET Long Running Task (22)	.NET Long Task (14)
.NET ThreadPool IO (18)	.NET TP I/O (11)
.NET SynchManager (18)	.NET Sync Mgr (13)

All other runtime thread names (.NET TP Worker, .NET Finalizer, .NET EventPipe, etc.) were already within the limit and are unchanged.

The rename of .NET Long Running Task → .NET Long Task is also applied in src/mono/browser/runtime/pthreads/worker-thread.ts, which hardcodes the name to identify long-running threads in the Mono browser WASM threading layer.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Shorten thread names that exceed the 15-char Linux limit</issue_title>
<issue_description>> [!NOTE]

This issue was created with Copilot assistance.

Linux limits thread names to 15 characters (plus null terminator) via pthread_setname_np. Several runtime thread names exceed this and get silently truncated, making them indistinguishable in debuggers and diagnostic tools like ps, top, and htop.

(macOS allows 63 chars, FreeBSD allows 32 — Linux is the strictest.)

Current Name	Len	Suggested Name	Len	Location
.NET Stack overflow trace logger	33	.NET SO Tracer	14	src/coreclr/vm/eepolicy.cpp
.NET Stack overflow create dump	32	.NET SO Dumper	14	src/coreclr/vm/excep.cpp
.NET Tiered Compilation Worker	30	.NET Tiered JIT	15	src/coreclr/vm/tieredcompilation.cpp
.NET Long Running Task	23	.NET Long Task	14	ThreadPoolTaskScheduler.cs
.NET ThreadPool IO	18	.NET TP I/O	12	PortableThreadPool.IO.Windows.cs
.NET SynchManager	17	.NET Synch Mgr	14	src/coreclr/pal/src/synchmgr/synchmanager.cpp
.NET TP Worker	14
.NET Finalizer	14
.NET EventPipe	14
.NET DebugPipe	14
.NET Debugger	13
.NET TP Gate	12
.NET TP Wait	12
JSWebWorker	11
.NET Timer	10

Note: The managed debugger may rely on some of these thread names to identify special threads. If so either they should be left unchanged or there will need to be a synchronized debugger change to match.
</issue_description>

Comments on the Issue (you are @copilot in this section)

@jkotas > .NET TC Worker

We should drop the "worker" from the name, it has very little information value. Once we do that, it can something more self-describing like ".NET Tiered JIT".

.NET LR Task

"LR" is very cryptic. Can this be something more self-describing like ".NET Long Task"?

.NET TP I/O

Windows specific. (We can still change the name to make it more similar to other TP names.)</comment_new>
<comment_new>@danmoseley
Any issues with debugger dependency or we can freely change?
I can kick copilot if there's no special considerations</comment_new>
<comment_new>@jkotas
We have tweaked the thread names a few times before and I do not recall debugger or diagnostic tools having an issue with that.</comment_new>

• Fixes Shorten thread names that exceed the 15-char Linux limit #125919

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[jkotas]

@copilot Review all code and tests in the repo for copies of these strings and update them as appropriate. Note that that string can be shortened.

For example, src\mono\browser\runtime\pthreads\worker-thread.ts has .NET Long Running Task hardcoded string that needs to be updated.

[Copilot]

@copilot Review all code and tests in the repo for copies of these strings and update them as appropriate. Note that that string can be shortened.

For example, `src\mono\browser\runtime\pthreads\wo...

Done in 02f058b. Updated src/mono/browser/runtime/pthreads/worker-thread.ts (the only other occurrence) — .NET Long Running Task → .NET Long Task. Verified no other copies of the old names remain anywhere in the repo.

[danmoseley]

@hoyosjs can you confirm no debugger dependency concerns?

[danmoseley]

Past changes like this
#75113

[Copilot]

Pull request overview

This PR shortens several internal runtime thread names to fit Linux’s 15-character pthread_setname_np limit so that thread names remain distinguishable in system tools and debuggers, and keeps the Mono browser WASM threading layer in sync for long-running thread identification.

Changes:

• Renames stack overflow helper threads to shorter, distinct names (.NET SO Tracer, .NET SO Dumper).
• Renames tiered compilation background worker thread to .NET Tiered JIT (15 chars).
• Renames managed long-running task thread, Windows threadpool I/O poller thread, and PAL SynchManager worker thread to shorter names (including syncing the WASM worker-thread identification string).

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/mono/browser/runtime/pthreads/worker-thread.ts	Updates the hardcoded long-running thread name check to match the new runtime thread name.
src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/ThreadPoolTaskScheduler.cs	Shortens the dedicated LongRunning task thread name.
src/libraries/System.Private.CoreLib/src/System/Threading/PortableThreadPool.IO.Windows.cs	Shortens the Windows IO completion poller thread name for consistency and readability.
src/coreclr/vm/tieredcompilation.cpp	Shortens the tiered compilation background worker thread name to fit Linux’s limit.
src/coreclr/vm/excep.cpp	Shortens the stack overflow “createdump” helper thread name to avoid truncation.
src/coreclr/vm/eepolicy.cpp	Shortens the stack overflow stack trace logging helper thread name to avoid truncation.
src/coreclr/pal/src/synchmgr/synchmanager.cpp	Shortens the synchronization manager worker thread name to avoid truncation.

[danmoseley]

I was curious what the synch manager is and apparently it's the PAL way of simulating Windows cross process synchronization primitives.