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boost::thread_resource_error improvements #427

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Merged
edolstra merged 2 commits into from
Apr 16, 2026
Merged

boost::thread_resource_error improvements #427

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aa8f61b
Executor: Make thread creation failure non-fatal
edolstra Apr 16, 2026
5c862d7
Limit default number of eval threads to 32
edolstra Apr 16, 2026
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14 changes: 12 additions & 2 deletions src/libexpr/parallel-eval.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -17,8 +17,10 @@ thread_local bool Executor::amWorkerThread{false};

unsigned int Executor::getEvalCores(const EvalSettings & evalSettings)
{
/* Note: the default number of cores is currently limited to 32
due to scalability bottlenecks. */
return evalSettings.evalProfilerMode != EvalProfilerMode::disabled ? 1
: evalSettings.evalCores == 0UL ? Settings::getDefaultCores()
: evalSettings.evalCores == 0UL ? std::min(32U, Settings::getDefaultCores())
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@cole-h cole-h Apr 16, 2026

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Would it be useful to add a small note explaining that this 32 figure is just because (as the commit message says) scalability sees diminishing returns? In case we ever fix these scalability issues, so we can again unlock much more parallelism...

: evalSettings.evalCores;
}

Expand All @@ -32,8 +34,16 @@ Executor::Executor(const EvalSettings & evalSettings)
{
debug("executor using %d threads", evalCores);
auto state(state_.lock());
// FIXME: create worker threads on demand?
for (size_t n = 0; n < evalCores; ++n)
createWorker(*state);
try {
createWorker(*state);
} catch (boost::thread_resource_error & e) {
if (n == 0)
throw Error("could not create any evaluator worker threads: %s", e.what());
warn("could only create %d evaluator worker threads: %s", n, e.what());
break;
}
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}

Executor::~Executor()
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