From 24497d08bc5aa0ee1f587b93ef46bb1838cb9b33 Mon Sep 17 00:00:00 2001
From: Alois Wohlschlager <alois1@gmx-topmail.de>
Date: Fri, 10 Oct 2025 16:20:28 +0200
Subject: [PATCH] nix-eval-jobs: use std::thread

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
---
 .../nix-eval-jobs/src/nix-eval-jobs.cc        | 52 +------------------
 1 file changed, 1 insertion(+), 51 deletions(-)

diff --git a/subprojects/nix-eval-jobs/src/nix-eval-jobs.cc b/subprojects/nix-eval-jobs/src/nix-eval-jobs.cc
index 0b9204475..f8a87fb86 100644
--- a/subprojects/nix-eval-jobs/src/nix-eval-jobs.cc
+++ b/subprojects/nix-eval-jobs/src/nix-eval-jobs.cc
@@ -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),