From a7c9e39f0f58a1dcd41475f5623f301f14e31da7 Mon Sep 17 00:00:00 2001
From: Rodrigo Kumpera <kumpera@gmail.com>
Date: Wed, 27 Sep 2017 17:30:49 -0700
Subject: [PATCH] [wasm] Implement GC support. Embedder must provide main loop
 pumping function request_gc_cycle.

---
 mono/metadata/sgen-mono.c |  4 ++++
 mono/metadata/sgen-stw.c  |  2 ++
 mono/sgen/sgen-conf.h     |  2 +-
 mono/sgen/sgen-gc.c       | 48 ++++++++++++++++++++++++++++++++++++++-
 4 files changed, 54 insertions(+), 2 deletions(-)

diff --git a/mono/metadata/sgen-mono.c b/mono/metadata/sgen-mono.c
index 4cd30493fff..df39ea5c567 100644
--- a/mono/metadata/sgen-mono.c
+++ b/mono/metadata/sgen-mono.c
@@ -2361,6 +2361,10 @@ sgen_client_scan_thread_data (void *start_nursery, void *end_nursery, gboolean p
 {
 	scan_area_arg_start = start_nursery;
 	scan_area_arg_end = end_nursery;
+#ifdef HOST_WASM
+	//Under WASM we don't scan thread stacks and we can't trust the values we find there either.
+	return;
+#endif
 
 	FOREACH_THREAD (info) {
 		int skip_reason = 0;
diff --git a/mono/metadata/sgen-stw.c b/mono/metadata/sgen-stw.c
index 48ce7f963ed..a8a1b9bf32c 100644
--- a/mono/metadata/sgen-stw.c
+++ b/mono/metadata/sgen-stw.c
@@ -70,6 +70,8 @@ update_current_thread_stack (void *start)
 
 #if !defined(MONO_CROSS_COMPILE) && MONO_ARCH_HAS_MONO_CONTEXT
 	MONO_CONTEXT_GET_CURRENT (info->client_info.ctx);
+#elif defined (HOST_WASM)
+	//nothing
 #else
 	g_error ("Sgen STW requires a working mono-context");
 #endif
diff --git a/mono/sgen/sgen-conf.h b/mono/sgen/sgen-conf.h
index 5e8866ffff8..47173bc29c9 100644
--- a/mono/sgen/sgen-conf.h
+++ b/mono/sgen/sgen-conf.h
@@ -104,7 +104,7 @@ typedef mword SgenDescriptor;
 #endif
 #endif
 
-#if defined (TARGET_WASM)
+#if defined (HOST_WASM)
 #define DEFAULT_MAJOR SGEN_MAJOR_SERIAL
 #define DEFAULT_SWEEP_MODE SGEN_SWEEP_SERIAL
 #elif defined(HAVE_CONC_GC_AS_DEFAULT)
diff --git a/mono/sgen/sgen-gc.c b/mono/sgen/sgen-gc.c
index d5416f0df36..4c3454823fd 100644
--- a/mono/sgen/sgen-gc.c
+++ b/mono/sgen/sgen-gc.c
@@ -2503,7 +2503,7 @@ sgen_ensure_free_space (size_t size, int generation)
  * LOCKING: Assumes the GC lock is held.
  */
 void
-sgen_perform_collection (size_t requested_size, int generation_to_collect, const char *reason, gboolean wait_to_finish, gboolean stw)
+sgen_perform_collection_inner (size_t requested_size, int generation_to_collect, const char *reason, gboolean wait_to_finish, gboolean stw)
 {
 	TV_DECLARE (gc_total_start);
 	TV_DECLARE (gc_total_end);
@@ -2582,6 +2582,52 @@ sgen_perform_collection (size_t requested_size, int generation_to_collect, const
 		sgen_restart_world (oldest_generation_collected);
 }
 
+#ifdef HOST_WASM
+
+typedef struct {
+	size_t requested_size;
+	int generation_to_collect;
+	const char *reason;
+} SgenGcRequest;
+
+static SgenGcRequest gc_request;
+static gboolean pending_request;
+
+extern void request_gc_cycle (void);
+
+#include <emscripten.h>
+
+EMSCRIPTEN_KEEPALIVE void
+mono_gc_pump_callback (void)
+{
+	if (!pending_request)
+		return;
+	pending_request = FALSE;
+	sgen_perform_collection_inner (gc_request.requested_size, gc_request.generation_to_collect, gc_request.reason, TRUE, TRUE);	
+}
+#endif
+
+void
+sgen_perform_collection (size_t requested_size, int generation_to_collect, const char *reason, gboolean wait_to_finish, gboolean stw)
+{
+#ifdef HOST_WASM
+	g_assert (stw); //can't handle non-stw mode (IE, domain unload)
+	//we ignore wait_to_finish
+	if (!pending_request || gc_request.generation_to_collect <= generation_to_collect) { //no active request or request was for a smaller part of the heap
+		gc_request.requested_size = requested_size;
+		gc_request.generation_to_collect = generation_to_collect;
+		gc_request.reason = reason;
+		if (!pending_request) {
+			request_gc_cycle ();
+			pending_request = TRUE;
+		}
+	}
+
+	degraded_mode = 1; //enable degraded mode so allocation can continue
+#else
+	sgen_perform_collection_inner (requested_size, generation_to_collect, reason, wait_to_finish, stw);
+#endif
+}
 /*
  * ######################################################################
  * ########  Memory allocation from the OS
-- 
2.25.1