Support external string GC types so XPConnect and other systems can optimize away copies (50602, r=jband).

js/src/jsOS240.def

@@ -615,6 +615,13 @@ EXPORTS
       JS_GetScriptPrincipals
       JS_IsAssigning
       JS_SetCharSetInfo
+;brendan@mozilla.org, 2-Sept-2000
+      JS_SetCallReturnValue2
+      JS_SetGCCallback
+      JS_SetGCCallbackRT
+      JS_AddExternalStringFinalizer
+      JS_RemoveExternalStringFinalizer
+      JS_NewExternalString
 ;
 ;
 ;00023:prmjtime (OFFSET:0x000dae0f, SIZE:0x00008986):

js/src/jsapi.c

@@ -1547,6 +1547,34 @@ JS_SetGCCallbackRT(JSRuntime *rt, JSGCCallback cb)
     return oldcb;
 }
 
+JS_PUBLIC_API(intN)
+JS_AddExternalStringFinalizer(JSStringFinalizeOp finalizer)
+{
+    return js_ChangeExternalStringFinalizer(NULL, finalizer);
+}
+
+JS_PUBLIC_API(intN)
+JS_RemoveExternalStringFinalizer(JSStringFinalizeOp finalizer)
+{
+    return js_ChangeExternalStringFinalizer(finalizer, NULL);
+}
+
+JS_PUBLIC_API(JSString *)
+JS_NewExternalString(JSContext *cx, jschar *chars, size_t length, intN type)
+{
+    JSString *str;
+
+    CHECK_REQUEST(cx);
+    JS_ASSERT(GCX_EXTERNAL_STRING <= type && type < (intN) GCX_NTYPES);
+
+    str = (JSString *) js_AllocGCThing(cx, (uintN) type);
+    if (!str)
+        return NULL;
+    str->length = length;
+    str->chars = chars;
+    return str;
+}
+
 /************************************************************************/
 
 JS_PUBLIC_API(void)

js/src/jsapi.h

@@ -18,7 +18,7 @@
  * Copyright (C) 1998 Netscape Communications Corporation. All
  * Rights Reserved.
  *
- * Contributor(s): 
+ * Contributor(s):
  *
  * Alternatively, the contents of this file may be used under the
  * terms of the GNU Public License (the "GPL"), in which case the
@@ -551,6 +551,45 @@ JS_SetGCCallback(JSContext *cx, JSGCCallback cb);
 extern JS_PUBLIC_API(JSGCCallback)
 JS_SetGCCallbackRT(JSRuntime *rt, JSGCCallback cb);
 
+/*
+ * Add an external string finalizer, one that understands struct JSString
+ * (from jsstr.h) and knows how to free or release the memory pointed at by
+ * its chars member.
+ *
+ * Return a nonnegative type index if there is room for finalizer in the
+ * global GC finalizers table, else return -1.  If the engine is compiled
+ * JS_THREADSAFE and used in a multi-threaded environment, this function must
+ * be invoked on the primordial thread only, at startup -- or else the entire
+ * program must single-thread itself while loading a module that calls this
+ * function.
+ */
+extern JS_PUBLIC_API(intN)
+JS_AddExternalStringFinalizer(JSStringFinalizeOp finalizer);
+
+/*
+ * Remove finalizer from the global GC finalizers table, returning its type
+ * code if found, -1 if not found.
+ *
+ * As with JS_AddExternalStringFinalizer, there is a threading restriction
+ * if you compile the engine JS_THREADSAFE: this function may be called for a
+ * given finalizer pointer on only one thread; different threads may call to
+ * remove distinct finalizers safely.
+ *
+ * You must ensure that all strings with finalizer's type have been collected
+ * before calling this function.  Otherwise, string data will be leaked by the
+ * GC, for want of a finalizer to call.
+ */
+extern JS_PUBLIC_API(intN)
+JS_RemoveExternalStringFinalizer(JSStringFinalizeOp finalizer);
+
+/*
+ * Create a new JSString whose chars member refers to external memory, i.e.,
+ * memory requiring special, type-specific finalization.  The type code must
+ * be a nonnegative return value from JS_AddExternalStringFinalizer.
+ */
+extern JS_PUBLIC_API(JSString *)
+JS_NewExternalString(JSContext *cx, jschar *chars, size_t length, intN type);
+
 /************************************************************************/
 
 /*
@@ -1223,7 +1262,7 @@ extern JS_PUBLIC_API(void)
 JS_SetLocaleCallbacks(JSContext *cx, JSLocaleCallbacks *callbacks);
 
 /* Return the address of the current locale callbacks struct. May be NULL. */
-extern JS_PUBLIC_API(JSLocaleCallbacks *) 
+extern JS_PUBLIC_API(JSLocaleCallbacks *)
 JS_GetLocaleCallbacks(JSContext *cx);
 
 /************************************************************************/

js/src/jsgc.c

@@ -82,6 +82,21 @@ typedef void (*GCFinalizeOp)(JSContext *cx, JSGCThing *thing);
 
 static GCFinalizeOp gc_finalizers[GCX_NTYPES];
 
+intN
+js_ChangeExternalStringFinalizer(JSStringFinalizeOp oldop,
+                                 JSStringFinalizeOp newop)
+{
+    uintN i;
+
+    for (i = GCX_EXTERNAL_STRING; i < GCX_NTYPES; i++) {
+        if (gc_finalizers[i] == (GCFinalizeOp) oldop) {
+            gc_finalizers[i] = (GCFinalizeOp) newop;
+            return (intN) i;
+        }
+    }
+    return -1;
+}
+
 #ifdef JS_GCMETER
 #define METER(x) x
 #else
@@ -94,7 +109,9 @@ js_InitGC(JSRuntime *rt, uint32 maxbytes)
     if (!gc_finalizers[GCX_OBJECT]) {
 	gc_finalizers[GCX_OBJECT] = (GCFinalizeOp)js_FinalizeObject;
 	gc_finalizers[GCX_STRING] = (GCFinalizeOp)js_FinalizeString;
+#ifdef DEBUG
 	gc_finalizers[GCX_DOUBLE] = (GCFinalizeOp)js_FinalizeDouble;
+#endif
     }
 
     JS_InitArenaPool(&rt->gcArenaPool, "gc-arena", GC_ARENA_SIZE,
@@ -479,13 +496,13 @@ gc_dump_thing(JSRuntime* rt, JSGCThing *thing, uint8 flags, GCMarkNode *prev,
         break;
       }
       case GCX_STRING:
+      case GCX_EXTERNAL_STRING:
+      default:
         fprintf(fp, "string %s", JS_GetStringBytes((JSString *)thing));
         break;
       case GCX_DOUBLE:
         fprintf(fp, "double %g", *(jsdouble *)thing);
         break;
-      case GCX_DECIMAL:
-        break;
     }
     fprintf(fp, " via %s\n", path);
     free(path);
@@ -686,9 +703,10 @@ gc_lock_marker(JSHashEntry *he, intN i, void *arg)
 JS_FRIEND_API(void)
 js_ForceGC(JSContext *cx)
 {
-    cx->newborn[GCX_OBJECT] = NULL;
-    cx->newborn[GCX_STRING] = NULL;
-    cx->newborn[GCX_DOUBLE] = NULL;
+    uintN i;
+
+    for (i = 0; i < GCX_NTYPES; i++)
+        cx->newborn[i] = NULL;
     cx->runtime->gcPoke = JS_TRUE;
     js_GC(cx, 0);
     JS_ArenaFinish();
@@ -703,6 +721,7 @@ js_GC(JSContext *cx, uintN gcflags)
     jsval v, *vp, *sp;
     jsuword begin, end;
     JSStackFrame *fp, *chain;
+    uintN i;
     void *mark;
     uint8 flags, *flagp;
     JSGCThing *thing, *final, **flp, **oflp;
@@ -913,6 +932,8 @@ restart:
 	GC_MARK(cx, acx->newborn[GCX_OBJECT], "newborn object", NULL);
 	GC_MARK(cx, acx->newborn[GCX_STRING], "newborn string", NULL);
 	GC_MARK(cx, acx->newborn[GCX_DOUBLE], "newborn double", NULL);
+	for (i = GCX_EXTERNAL_STRING; i < GCX_NTYPES; i++)
+            GC_MARK(cx, acx->newborn[i], "newborn external string", NULL);
 #if JS_HAS_EXCEPTIONS
 	if (acx->throwing && JSVAL_IS_GCTHING(acx->exception))
 	    GC_MARK(cx, JSVAL_TO_GCTHING(acx->exception), "exception", NULL);

js/src/jsgc.h

@@ -43,19 +43,20 @@
 JS_BEGIN_EXTERN_C
 
 /* GC thing type indexes. */
-#define GCX_OBJECT      0                       /* JSObject */
-#define GCX_STRING      1                       /* JSString */
-#define GCX_DOUBLE      2                       /* jsdouble */
-#define GCX_DECIMAL     3                       /* JSDecimal */
-#define GCX_NTYPES      4
+#define GCX_OBJECT              0               /* JSObject */
+#define GCX_STRING              1               /* JSString */
+#define GCX_DOUBLE              2               /* jsdouble */
+#define GCX_EXTERNAL_STRING     3               /* JSString w/ external chars */
+#define GCX_NTYPES_LOG2         3
+#define GCX_NTYPES              JS_BIT(GCX_NTYPES_LOG2)
 
 /* GC flag definitions (type index goes in low bits). */
-#define GCF_TYPEMASK    JS_BITMASK(2)           /* use low bits for type */
-#define GCF_MARK        JS_BIT(2)               /* mark bit */
-#define GCF_FINAL       JS_BIT(3)               /* in finalization bit */
-#define GCF_LOCKBIT     4                       /* lock bit shift and mask */
-#define GCF_LOCKMASK    (JS_BITMASK(4) << GCF_LOCKBIT)
-#define GCF_LOCK        JS_BIT(GCF_LOCKBIT)     /* lock request bit in API */
+#define GCF_TYPEMASK    JS_BITMASK(GCX_NTYPES_LOG2)
+#define GCF_MARK        JS_BIT(GCX_NTYPES_LOG2)
+#define GCF_FINAL       JS_BIT(GCX_NTYPES_LOG2 + 1)
+#define GCF_LOCKSHIFT   (GCX_NTYPES_LOG2 + 2)   /* lock bit shift and mask */
+#define GCF_LOCKMASK    (JS_BITMASK(8 - GCF_LOCKSHIFT) << GCF_LOCKSHIFT)
+#define GCF_LOCK        JS_BIT(GCF_LOCKSHIFT)   /* lock request bit in API */
 
 #if 1
 /*
@@ -67,6 +68,10 @@ JS_BEGIN_EXTERN_C
 #define GC_POKE(cx, oldval) ((cx)->runtime->gcPoke = JSVAL_IS_GCTHING(oldval))
 #endif
 
+extern intN
+js_ChangeExternalStringFinalizer(JSStringFinalizeOp oldop,
+                                 JSStringFinalizeOp newop);
+
 extern JSBool
 js_InitGC(JSRuntime *rt, uint32 maxbytes);
 

js/src/jspubtd.h

@@ -170,6 +170,9 @@ typedef JSBool
 typedef void
 (* CRT_CALL JSFinalizeOp)(JSContext *cx, JSObject *obj);
 
+typedef void
+(* CRT_CALL JSStringFinalizeOp)(JSContext *cx, JSString *str);
+
 typedef JSObjectOps *
 (* CRT_CALL JSGetObjectOps)(JSContext *cx, JSClass *clasp);