From 2c53ef1bfee7c7afea889f42b9ef13e1007ad228 Mon Sep 17 00:00:00 2001
From: Yorick van Pelt <yorick@yorickvanpelt.nl>
Date: Fri, 3 Feb 2023 17:50:01 +0100
Subject: [PATCH] Disable GC inside coroutines on mac OS

---
 src/libexpr/eval.cc      | 20 ++++++++++++++++++++
 src/libutil/serialise.cc | 38 +++++++++++++++++++++++++++++++++-----
 src/libutil/serialise.hh | 10 ++++++++++
 3 files changed, 63 insertions(+), 5 deletions(-)

diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 7f2065656..f7c056998 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -345,6 +345,20 @@ static Symbol getName(const AttrName & name, EvalState & state, Env & env)
 }
 
 
+class BoehmDisableGC : public DisableGC {
+public:
+    BoehmDisableGC() {
+#if HAVE_BOEHMGC
+        GC_disable();
+#endif
+    };
+    virtual ~BoehmDisableGC() override {
+#if HAVE_BOEHMGC
+        GC_enable();
+#endif
+    };
+};
+
 static bool gcInitialised = false;
 
 void initGC()
@@ -368,6 +382,12 @@ void initGC()
 
     StackAllocator::defaultAllocator = &boehmGCStackAllocator;
 
+
+    /* Used to disable GC when entering coroutines on macOS */
+    DisableGC::create = []() {
+        return std::dynamic_pointer_cast<DisableGC>(std::make_shared<BoehmDisableGC>());
+    };
+
     /* Set the initial heap size to something fairly big (25% of
        physical RAM, up to a maximum of 384 MiB) so that in most cases
        we don't need to garbage collect at all.  (Collection has a
diff --git a/src/libutil/serialise.cc b/src/libutil/serialise.cc
index 7476e6f6c..fac2a0df8 100644
--- a/src/libutil/serialise.cc
+++ b/src/libutil/serialise.cc
@@ -186,6 +186,10 @@ static DefaultStackAllocator defaultAllocatorSingleton;
 StackAllocator *StackAllocator::defaultAllocator = &defaultAllocatorSingleton;
 
 
+std::shared_ptr<DisableGC> (*DisableGC::create)() = []() {
+    return std::dynamic_pointer_cast<DisableGC>(std::make_shared<DisableGC>());
+};
+
 std::unique_ptr<FinishSink> sourceToSink(std::function<void(Source &)> fun)
 {
     struct SourceToSink : FinishSink
@@ -206,7 +210,11 @@ std::unique_ptr<FinishSink> sourceToSink(std::function<void(Source &)> fun)
             if (in.empty()) return;
             cur = in;
 
-            if (!coro)
+            if (!coro) {
+#if __APPLE__
+                /* Disable GC when entering the coroutine on macOS, since it doesn't find the main thread stack in this case */
+                auto disablegc = DisableGC::create();
+#endif
                 coro = coro_t::push_type(VirtualStackAllocator{}, [&](coro_t::pull_type & yield) {
                     LambdaSource source([&](char *out, size_t out_len) {
                         if (cur.empty()) {
@@ -223,17 +231,28 @@ std::unique_ptr<FinishSink> sourceToSink(std::function<void(Source &)> fun)
                     });
                     fun(source);
                 });
+            }
 
             if (!*coro) { abort(); }
 
-            if (!cur.empty()) (*coro)(false);
+            if (!cur.empty()) {
+#if __APPLE__
+                auto disablegc = DisableGC::create();
+#endif
+                (*coro)(false);
+            }
         }
 
         void finish() override
         {
             if (!coro) return;
             if (!*coro) abort();
-            (*coro)(true);
+            {
+#if __APPLE__
+                auto disablegc = DisableGC::create();
+#endif
+                (*coro)(true);
+            }
             if (*coro) abort();
         }
     };
@@ -264,18 +283,27 @@ std::unique_ptr<Source> sinkToSource(
 
         size_t read(char * data, size_t len) override
         {
-            if (!coro)
+            if (!coro) {
+#if __APPLE__
+                auto disablegc = DisableGC::create();
+#endif
                 coro = coro_t::pull_type(VirtualStackAllocator{}, [&](coro_t::push_type & yield) {
                     LambdaSink sink([&](std::string_view data) {
                         if (!data.empty()) yield(std::string(data));
                     });
                     fun(sink);
                 });
+            }
 
             if (!*coro) { eof(); abort(); }
 
             if (pos == cur.size()) {
-                if (!cur.empty()) (*coro)();
+                if (!cur.empty()) {
+#if __APPLE__
+                    auto disablegc = DisableGC::create();
+#endif
+                    (*coro)();
+                }
                 cur = coro->get();
                 pos = 0;
             }
diff --git a/src/libutil/serialise.hh b/src/libutil/serialise.hh
index 2cf527023..612196fd2 100644
--- a/src/libutil/serialise.hh
+++ b/src/libutil/serialise.hh
@@ -551,4 +551,14 @@ struct StackAllocator {
     static StackAllocator *defaultAllocator;
 };
 
+/* Disabling GC when entering a coroutine (on macos).
+   ::create is to avoid boehm gc dependency in libutil.
+ */
+class DisableGC {
+public:
+    DisableGC() {};
+    virtual ~DisableGC() {};
+    static std::shared_ptr<DisableGC> (*create)();
+};
+
 }