From 11d467fecdc325b8d8ff75ce4c9b0ef1f0a5e011 Mon Sep 17 00:00:00 2001
From: Puck Meerburg <puck@puckipedia.com>
Date: Sun, 9 Jun 2024 13:20:20 +0000
Subject: [PATCH] Use our own Thread struct instead of std::thread

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.
---
 src/nix-eval-jobs.cc | 54 +++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 51 insertions(+), 3 deletions(-)

diff --git a/src/nix-eval-jobs.cc b/src/nix-eval-jobs.cc
index e2b204b..ca935af 100644
--- a/src/nix-eval-jobs.cc
+++ b/src/nix-eval-jobs.cc
@@ -8,6 +8,7 @@
 #include <sys/wait.h>
 #include <nlohmann/json.hpp>
 #include <errno.h>
+#include <pthread.h>
 #include <signal.h>
 #include <stdlib.h>
 #include <string.h>
@@ -24,7 +25,6 @@
 #include <lix/libutil/ref.hh>
 #include <lix/libstore/store-api.hh>
 #include <map>
-#include <thread>
 #include <condition_variable>
 #include <filesystem>
 #include <exception>
@@ -99,6 +99,54 @@ struct Proc {
     ~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;
@@ -332,10 +380,10 @@ int main(int argc, char **argv) {
         Sync<State> state_;
 
         /* Start a collector thread per worker process. */
-        std::vector<std::thread> threads;
+        std::vector<Thread> threads;
         std::condition_variable wakeup;
         for (size_t i = 0; i < myArgs.nrWorkers; i++) {
-            threads.emplace_back(collector, std::ref(state_), std::ref(wakeup));
+            threads.emplace_back(std::bind(collector, std::ref(state_), std::ref(wakeup)));
         }
 
         for (auto &thread : threads)