From 2ff8acbe1afff28cb152c1a306971c8c57d03c94 Mon Sep 17 00:00:00 2001
From: Bob Nystrom <robert@stuffwithstuff.com>
Date: Thu, 29 Oct 2015 07:38:09 -0700
Subject: [PATCH] Tweak a few things in the new GC.

- Make sure it handles an empty gray set.
- Make sure growing the gray stack doesn't itself trigger a GC.
- Make sure it works when stress testing is enabled.
- Ensure the tests kick off a GC.
---
 src/vm/wren_value.c                   | 17 ++++++++---------
 src/vm/wren_vm.c                      | 18 +++++++-----------
 src/vm/wren_vm.h                      |  4 ++--
 test/language/deeply_nested_gc.wren   |  3 ++-
 test/language/many_reallocations.wren |  4 +++-
 5 files changed, 22 insertions(+), 24 deletions(-)

diff --git a/src/vm/wren_value.c b/src/vm/wren_value.c
index 0f3b0b2a..58f44588 100644
--- a/src/vm/wren_value.c
+++ b/src/vm/wren_value.c
@@ -867,15 +867,14 @@ void wrenGrayObj(WrenVM* vm, Obj* obj)
   
   // Add it to the gray list so it can be recursively explored for
   // more marks later.
-  if (vm->grayDepth >= vm->maxGray)
+  if (vm->grayCount >= vm->grayCapacity)
   {
-    size_t oldSize = vm->maxGray * sizeof(Obj*);
-    size_t newSize = vm->grayDepth * 2 * sizeof(Obj*);
-    vm->gray = (Obj**)wrenReallocate(vm, vm->gray, oldSize, newSize);
-    vm->maxGray = vm->grayDepth * 2;
+    vm->grayCapacity = vm->grayCount * 2;
+    vm->gray = vm->config.reallocateFn(vm->gray,
+                                       vm->grayCapacity * sizeof(Obj*));
   }
   
-  vm->gray[vm->grayDepth++] = obj;
+  vm->gray[vm->grayCount++] = obj;
 }
 
 void wrenGrayValue(WrenVM* vm, Value value)
@@ -1095,12 +1094,12 @@ static void blackenObject(WrenVM* vm, Obj* obj)
 
 void wrenBlackenObjects(WrenVM* vm)
 {
-  do
+  while (vm->grayCount > 0)
   {
     // Pop an item from the gray stack.
-    Obj* obj = vm->gray[--vm->grayDepth];
+    Obj* obj = vm->gray[--vm->grayCount];
     blackenObject(vm, obj);
-  } while (vm->grayDepth > 0);
+  }
 }
 
 void wrenFreeObj(WrenVM* vm, Obj* obj)
diff --git a/src/vm/wren_vm.c b/src/vm/wren_vm.c
index 0ef7f108..de3e1a6e 100644
--- a/src/vm/wren_vm.c
+++ b/src/vm/wren_vm.c
@@ -46,29 +46,25 @@ void wrenInitConfiguration(WrenConfiguration* config)
   config->heapGrowthPercent = 50;
 }
 
-static void initializeGC(WrenVM* vm)
-{
-  vm->gray = (Obj**)wrenReallocate(vm, NULL, 0, 5 * sizeof(Obj*));
-  vm->grayDepth = 0;
-  vm->maxGray = 5;
-}
-
 WrenVM* wrenNewVM(WrenConfiguration* config)
 {
   WrenVM* vm = (WrenVM*)config->reallocateFn(NULL, sizeof(*vm));
   memset(vm, 0, sizeof(WrenVM));
   memcpy(&vm->config, config, sizeof(WrenConfiguration));
 
+  // TODO: Should we allocate and free this during a GC?
+  vm->grayCount = 0;
+  // TODO: Tune this.
+  vm->grayCapacity = 4;
+  vm->gray = vm->config.reallocateFn(NULL, vm->grayCapacity * sizeof(Obj*));
   vm->nextGC = config->initialHeapSize;
-
+  
   wrenSymbolTableInit(&vm->methodNames);
 
   vm->modules = wrenNewMap(vm);
 
   wrenInitializeCore(vm);
 
-  initializeGC(vm);
-
   // TODO: Lazy load these.
   #if WREN_OPT_META
     wrenLoadMetaModule(vm);
@@ -94,7 +90,7 @@ void wrenFreeVM(WrenVM* vm)
   }
 
   // Free up the GC gray set.
-  wrenReallocate(vm, vm->gray, vm->maxGray * sizeof(Obj*), 0);
+  vm->gray = vm->config.reallocateFn(vm->gray, 0);
 
   // Tell the user if they didn't free any handles. We don't want to just free
   // them here because the host app may still have pointers to them that they
diff --git a/src/vm/wren_vm.h b/src/vm/wren_vm.h
index 3c0ec5c1..9b613a80 100644
--- a/src/vm/wren_vm.h
+++ b/src/vm/wren_vm.h
@@ -72,8 +72,8 @@ struct WrenVM
   // The "gray" set for the garbage collector. This is the stack of unprocessed
   // objects while a garbage collection pass is in process.
   Obj** gray;
-  int grayDepth;
-  int maxGray;
+  int grayCount;
+  int grayCapacity;
 
   // The list of temporary roots. This is for temporary or new objects that are
   // not otherwise reachable but should not be collected.
diff --git a/test/language/deeply_nested_gc.wren b/test/language/deeply_nested_gc.wren
index c40fa4c7..04bd443c 100644
--- a/test/language/deeply_nested_gc.wren
+++ b/test/language/deeply_nested_gc.wren
@@ -4,4 +4,5 @@ for (i in 1..400000) {
   head = { "next" : head }
 }
 
-System.print("done") // expect: done
\ No newline at end of file
+System.gc()
+System.print("done") // expect: done
diff --git a/test/language/many_reallocations.wren b/test/language/many_reallocations.wren
index 06a96285..cb9b28d5 100644
--- a/test/language/many_reallocations.wren
+++ b/test/language/many_reallocations.wren
@@ -10,5 +10,7 @@ for (i in 1..1000) {
   }
   found.add(bar)
 }
+
+System.gc()
 System.print(found.all {|i| i == 1337}) // expect: true
-System.print("DONE!") // expect: DONE!
+System.print("done") // expect: done