Stack thread

[graydon]

This adds a new StackThread type that works like std::thread but takes a stack size as first argument. It then uses that in BatchExecutor with an 8MiB stack. The point here is just to avoid worker-thread stack size variability across platforms, which we've seen from time to time in the past.

[Copilot]

Pull request overview

Adds a cross-platform StackThread abstraction with configurable stack sizes and uses it to standardize BatchExecutor worker stacks at 8 MiB.

Changes:

• Implements thread lifecycle, naming, IDs, and native handles.
• Migrates BatchExecutor workers from std::thread.
• Adds StackThread unit tests.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 5 comments.

File	Description
src/util/StackThread.h	Implements the configurable-stack thread abstraction.
src/util/test/StackThreadTests.cpp	Tests thread API behavior and Linux stack sizing.
src/util/BatchExecutor.h	Changes worker storage to StackThread.
src/util/BatchExecutor.cpp	Creates workers with 8 MiB stacks.

Comments suppressed due to low confidence (1)

src/util/StackThread.h:546

• pthread_create may run the trampoline before returning, while mThread, mJoinable, and mId are assigned only afterward. A callable that captures the StackThread under construction can observe or race with those writes, unlike std::thread's constructor synchronization guarantee. Gate payload->run() on a startup barrier that is released only after all object state has been published.

        rc = ::pthread_create(&tid, &attr, &detail::trampoline, payload.get());