#6014 Reduce shutdown delays on thread cleanup

[akleshchev]

Viewer runs a lot of different threads and each one was waiting 100ms on shutdown. Watchdog was waiting for internal sleep to finish.

[Copilot]

Pull request overview

This PR reduces viewer shutdown delays by allowing long-sleeping/background threads to exit more promptly during cleanup, notably by signaling the watchdog earlier and adding a bounded wait for queued-thread shutdown.

Changes:

• Add LLWatchdog::shutdown() and call it earlier during LLAppViewer::cleanup() to reduce watchdog-related shutdown waiting.
• Add a timed LLQueuedThread::waitOnPending(F32 max_time_sec) overload and use it for sTextureFetch shutdown.
• Reduce LLThread::shutdown() polling sleep interval from 100ms to 10ms (6s total wait before forced termination).

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
indra/newview/llappviewer.cpp	Signals watchdog shutdown earlier; bounds texture fetch pending-wait during shutdown.
indra/llcommon/llwatchdog.h	Declares new LLWatchdog::shutdown() API.
indra/llcommon/llwatchdog.cpp	Implements watchdog shutdown and adjusts timer-thread stop behavior.
indra/llcommon/llthread.cpp	Decreases shutdown polling sleep interval to reduce teardown delays.
indra/llcommon/llqueuedthread.h	Adds timed waitOnPending() overload declaration.
indra/llcommon/llqueuedthread.cpp	Implements timed waitOnPending() to prevent unbounded shutdown waits.

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[akleshchev]

May be I will just remove the string, but either way, no point locking it. Either thread is already in and will rewrite to a comparable value; thread is about to run and has plenty of time so won't hurt the shutdown; or value gets set and next run will be fast.