Merge pull request #8179 from tweag/disable-gc-on-coroutine

disable gc on coroutine

src/libexpr/eval.cc

@@ -344,6 +344,22 @@ static Symbol getName(const AttrName & name, EvalState & state, Env & env)
     }
 }
 
+#if HAVE_BOEHMGC
+/* Disable GC while this object lives. Used by CoroutineContext.
+ *
+ * Boehm keeps a count of GC_disable() and GC_enable() calls,
+ * and only enables GC when the count matches.
+ */
+class BoehmDisableGC {
+public:
+    BoehmDisableGC() {
+        GC_disable();
+    };
+    ~BoehmDisableGC() {
+        GC_enable();
+    };
+};
+#endif
 
 static bool gcInitialised = false;
 
@@ -368,6 +384,15 @@ void initGC()
 
     StackAllocator::defaultAllocator = &boehmGCStackAllocator;
 
+
+#if NIX_BOEHM_PATCH_VERSION != 1
+    printTalkative("Unpatched BoehmGC, disabling GC inside coroutines");
+    /* Used to disable GC when entering coroutines on macOS */
+    create_coro_gc_hook = []() -> std::shared_ptr<void> {
+        return std::make_shared<BoehmDisableGC>();
+    };
+#endif
+
     /* 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

src/libutil/serialise.cc

@@ -186,6 +186,22 @@ static DefaultStackAllocator defaultAllocatorSingleton;
 StackAllocator *StackAllocator::defaultAllocator = &defaultAllocatorSingleton;
 
 
+std::shared_ptr<void> (*create_coro_gc_hook)() = []() -> std::shared_ptr<void> {
+    return {};
+};
+
+/* This class is used for entry and exit hooks on coroutines */
+class CoroutineContext {
+    /* Disable GC when entering the coroutine without the boehm patch,
+     * since it doesn't find the main thread stack in this case.
+     * std::shared_ptr<void> performs type-erasure, so it will call the right
+     * deleter. */
+    const std::shared_ptr<void> coro_gc_hook = create_coro_gc_hook();
+public:
+    CoroutineContext() {};
+    ~CoroutineContext() {};
+};
+
 std::unique_ptr<FinishSink> sourceToSink(std::function<void(Source &)> fun)
 {
     struct SourceToSink : FinishSink
@@ -206,7 +222,8 @@ std::unique_ptr<FinishSink> sourceToSink(std::function<void(Source &)> fun)
             if (in.empty()) return;
             cur = in;
 
-            if (!coro)
+            if (!coro) {
+                CoroutineContext ctx;
                 coro = coro_t::push_type(VirtualStackAllocator{}, [&](coro_t::pull_type & yield) {
                     LambdaSource source([&](char *out, size_t out_len) {
                         if (cur.empty()) {
@@ -223,17 +240,24 @@ std::unique_ptr<FinishSink> sourceToSink(std::function<void(Source &)> fun)
                     });
                     fun(source);
                 });
+            }
 
             if (!*coro) { abort(); }
 
-            if (!cur.empty()) (*coro)(false);
+            if (!cur.empty()) {
+                CoroutineContext ctx;
+                (*coro)(false);
+            }
         }
 
         void finish() override
         {
             if (!coro) return;
             if (!*coro) abort();
-            (*coro)(true);
+            {
+                CoroutineContext ctx;
+                (*coro)(true);
+            }
             if (*coro) abort();
         }
     };
@@ -264,18 +288,23 @@ std::unique_ptr<Source> sinkToSource(
 
         size_t read(char * data, size_t len) override
         {
-            if (!coro)
+            if (!coro) {
+                CoroutineContext ctx;
                 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()) {
+                    CoroutineContext ctx;
+                    (*coro)();
+                }
                 cur = coro->get();
                 pos = 0;
             }

src/libutil/serialise.hh

@@ -551,4 +551,10 @@ struct StackAllocator {
     static StackAllocator *defaultAllocator;
 };
 
+/* Disabling GC when entering a coroutine (without the boehm patch).
+   mutable to avoid boehm gc dependency in libutil.
+ */
+extern std::shared_ptr<void> (*create_coro_gc_hook)();
+
+
 }