From 301c949362d243bb6b69956355e0e7ecccc43ce4 Mon Sep 17 00:00:00 2001
From: Teddy <ted.sybil@gmail.com>
Date: Mon, 12 Aug 2013 17:42:51 +0800
Subject: adding gc framework

---
 gc.cpp | 83 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 gc.h   | 31 +++++++++++++++++++++++++
 2 files changed, 114 insertions(+)
 create mode 100644 gc.cpp
 create mode 100644 gc.h

diff --git a/gc.cpp b/gc.cpp
new file mode 100644
index 0000000..4a3dd89
--- /dev/null
+++ b/gc.cpp
@@ -0,0 +1,83 @@
+#include "gc.h"
+#include "exc.h"
+#include "consts.h"
+
+#ifdef GC_DEBUG
+#include <cstdio>
+typedef unsigned long long ull;
+#endif
+
+static EvalObj *gcq[GC_QUEUE_SIZE];
+
+GarbageCollector::PendingEntry::PendingEntry(
+        EvalObj *_obj, PendingEntry *_next) : obj(_obj), next(_next) {}
+
+
+void GarbageCollector::expose(EvalObj *ptr) {
+    bool flag = mapping.count(ptr);
+    if (flag)
+    {
+        if (!--mapping[ptr])
+        {
+#ifdef GC_DEBUG
+            fprintf(stderr, "GC: 0x%llx pending. \n", (ull)ptr);
+#endif
+            pending_list = new PendingEntry(ptr, pending_list);
+            if (++pend_cnt == GC_QUEUE_SIZE >> 1)
+                force();    // the gc queue may overflow
+        }
+    }
+}
+
+void GarbageCollector::force() {
+    EvalObj **l = gcq, **r = l;
+    for (PendingEntry *p = pending_list, *np; p; p = np)
+    {
+        np = p->next;
+        *r++ = p->obj;
+        delete p;
+    }   // fetch the pending pointers in the list
+    // clear the list
+    pending_list = NULL;
+
+#ifdef GC_DEBUG
+    size_t cnt = 0;
+    fprintf(stderr, "GC: Forcing the clear process...\n");
+#endif
+    for (; l != r; l++)
+    {
+#ifdef GC_DEBUG
+        fprintf(stderr, "GC: destroying space 0x%llx. \n", (ull)*l);
+        cnt++;
+#endif
+        delete *l;
+        // maybe it's a complex structure, 
+        // so that more pointers are reported
+        for (PendingEntry *p = pending_list, *np; p; p = np)
+        {
+            np = p->next;
+            *r++ = p->obj;
+            if (r == gcq + GC_QUEUE_SIZE)
+                throw NormalError(RUN_ERR_GC_OVERFLOW);
+            delete p;
+        }   
+        pending_list = NULL;
+    }
+#ifdef GC_DEBUG
+    fprintf(stderr, "GC: Forced clear, %lu objects are freed\n", cnt);
+#endif
+}
+
+EvalObj *GarbageCollector::attach(EvalObj *ptr) {
+    if (!ptr) return NULL;   // NULL pointer
+    bool flag = mapping.count(ptr);
+    if (flag) mapping[ptr]++;
+    else mapping[ptr] = 1;
+#ifdef GC_DEBUG
+    fprintf(stderr, "GC: 0x%llx attached. count = %lu \"%s\"\n", 
+            (ull)ptr, mapping[ptr], ptr->ext_repr().c_str());
+#endif
+    return ptr; // passing through
+}
+
+GarbageCollector gc;
diff --git a/gc.h b/gc.h
new file mode 100644
index 0000000..417462f
--- /dev/null
+++ b/gc.h
@@ -0,0 +1,31 @@
+#ifndef GC_H
+#define GC_H
+
+#include "model.h"
+#include <map>
+
+const int GC_QUEUE_SIZE = 262144;
+
+typedef std::map<EvalObj*, size_t> EvalObj2Int;
+
+class GarbageCollector {
+
+    struct PendingEntry {
+        EvalObj *obj;
+        PendingEntry *next;
+        PendingEntry(EvalObj *obj, PendingEntry *next);
+    };
+
+    EvalObj2Int mapping;
+    size_t pend_cnt;
+    PendingEntry *pending_list;
+
+    public:
+    void force();
+    void expose(EvalObj *ptr);
+    EvalObj *attach(EvalObj *ptr);
+};
+
+extern GarbageCollector gc;
+
+#endif
-- 
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