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nix-eval-jobs: use std::thread

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As the worker processes are now properly spawned using fork-exec, they no
longer inherit the stack size from the non-main coordinator thread, but get a
main thread with reasonable stack size on their own. For this reason the
coordinator threads can use the default stack size, and turn std::thread can be
used as the only reason for the custom wrapper was to enlarge the stack.

Change-Id: I1192474885abe9b0625ac483840b6e1a6a6a6964
This commit is contained in:
Alois Wohlschlager
2025-11-29 11:25:19 +01:00
parent 258c5b76eb
commit 24497d08bc
1 changed files with 1 additions and 51 deletions
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subprojects/nix-eval-jobs/src/nix-eval-jobs.cc
+1 -51
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@@ -92,56 +92,6 @@ struct Proc {
}
};
// We'd highly prefer using std::thread here; but this won't let us configure the stack
// size. macOS uses 512KiB size stacks for non-main threads, and musl defaults to 128k.
// While Nix configures a 64MiB size for the main thread, this doesn't propagate to the
// threads we launch here. It turns out, running the evaluator under an anemic stack of
// 0.5MiB has it overflow way too quickly. Hence, we have our own custom Thread struct.
struct Thread {
pthread_t thread;
Thread(const Thread &) = delete;
Thread(Thread &&) noexcept = default;
Thread(std::function<void(void)> f) {
int s;
pthread_attr_t attr;
auto func = std::make_unique<std::function<void(void)>>(std::move(f));
if ((s = pthread_attr_init(&attr)) != 0) {
throw SysError(s, "calling pthread_attr_init");
}
if ((s = pthread_attr_setstacksize(&attr, 64 * 1024 * 1024)) != 0) {
throw SysError(s, "calling pthread_attr_setstacksize");
}
if ((s = pthread_create(&thread, &attr, Thread::init,
func.release())) != 0) {
throw SysError(s, "calling pthread_launch");
}
if ((s = pthread_attr_destroy(&attr)) != 0) {
throw SysError(s, "calling pthread_attr_destroy");
}
}
void join() {
int s;
s = pthread_join(thread, nullptr);
if (s != 0) {
throw SysError(s, "calling pthread_join");
}
}
private:
static void *init(void *ptr) {
std::unique_ptr<std::function<void(void)>> func;
func.reset(static_cast<std::function<void(void)> *>(ptr));
(*func)();
return 0;
}
};
struct State {
std::set<JSON> todo = JSON::array({JSON::array()});
std::set<JSON> active;
@@ -382,7 +332,7 @@ int main(int argc, char **argv) {
Sync<State> state_;
/* Start a collector thread per worker process. */
std::vector<Thread> threads;
std::vector<std::thread> threads;
std::condition_variable wakeup;
for (size_t i = 0; i < myArgs.nrWorkers; i++) {
threads.emplace_back(std::bind(collector, std::ref(myArgs),