macOS: add ThreadSupport (no-op suspend/resume)#3036
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The Linux ThreadSupport suspends/resumes threads via a SIGUSR1 handler plus getcontext()/ucontext_t, which has no portable macOS equivalent. Add a macOS ThreadSupport.cpp providing no-op Suspend()/Resume() and the thread setup/start plumbing, and wire it into the Mac threading sources. Performance-core preference is handled separately as a QoS hint in Threading::SetAffinity (the main and worker threads reach it via SetAffinityHelper), so it is not duplicated here. Mac-only: the file is in sources_engine_System_Threading_Mac, so Windows and Linux builds are unaffected.
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What
Adds
rts/System/Platform/Mac/ThreadSupport.cppand wires it into the Mac threading sources.The Linux
ThreadSupportsuspends/resumes threads via aSIGUSR1signal handler plusgetcontext()/ucontext_t— none of which has a portable macOS equivalent. This macOS version provides:Suspend()/Resume()as no-ops (macOS has no signal-based thread suspend).ThreadStart/SetupCurrentThreadControls— the thread setup/start plumbing (create theThreadControls, recordpthread_self(), signal initialization, run the task).QoS / performance cores
Deliberately not handled here. Performance-core preference is a QoS hint applied in
Threading::SetAffinity()(see the macOS affinity change), which the main and worker threads already reach viaSetAffinityHelper()(ThreadPool.cpp). Keeping it in one place avoids applying the QoS class twice.CMake
On
APPLE,sources_engine_System_Platform_Macpreviously pulled inPlatform/Linux/ThreadSupport.cpp— which doesn't compile on macOS (it usesSYS_gettid/sigaction/ucontext). This swaps that out: the newMac/ThreadSupport.cppis added tosources_engine_System_Threading_Mac, and the Linux file is dropped fromsources_engine_System_Platform_Mac(otherwise both would compile on APPLE → duplicate symbols).Cross-platform safety
Mac-only: the only lists touched are the
*_Macones, used solely underif(APPLE). Windows and Linux builds are byte-for-byte unaffected.Adapted from the macOS bring-up (#2991) as a standalone, reviewable piece (minus the QoS, which lives with the affinity change).