Re: Rhino1.5.R1: problems with multithreaded embedded application.
Date:
Mon, 03 Jul 2000 14:38:56 -0400
From:
Norris Boyd <nboyd@atg.com>
Organization:
Art Technology Group
To:
Fergus Gallagher <Fergus.Gallagher@orbisuk.com>
Newsgroups:
netscape.public.mozilla.jseng
References:
1
You found a bug in Rhino; I wonder if others have been running into the same thing.
The problem is with a class called LazilyLoadedCtor. I wrote this class to reduce the
time
required by initStandardObjects by only creating standard objects when the associated
constructors are first accessed. The problem is that this class was not threadsafe.
I've
made changes to that class, and to ScriptableObject as well. The design of dynamic
properties calling getters and setters (which LazilyLoadedCtor uses) didn't really
allow
any way for the getter/setter to replace itself without a thread hazard. I've now
extended
setters so that they can return a value which replaces the getter/setter to avoid this
problem.
Thanks for finding this problem. There have been a couple of other reports of problems
in
this area, so I hope this will fix them.
The patch follows.
--N
Index: LazilyLoadedCtor.java
===================================================================
RCS file: /cvsroot/mozilla/js/rhino/org/mozilla/javascript/LazilyLoadedCtor.java,v
retrieving revision 1.1
diff -u -r1.1 LazilyLoadedCtor.java
--- LazilyLoadedCtor.java 2000/02/29 21:34:37 1.1
+++ LazilyLoadedCtor.java 2000/07/03 18:31:03
@@ -58,9 +58,12 @@
}
public Object getProperty(ScriptableObject obj) {
- obj.delete(ctorName);
try {
- ScriptableObject.defineClass(obj, Class.forName(className));
+ synchronized (obj) {
+ if (!isReplaced)
+ ScriptableObject.defineClass(obj, Class.forName(className));
+ isReplaced = true;
+ }
}
catch (ClassNotFoundException e) {
throw WrappedException.wrapException(e);
@@ -83,11 +86,14 @@
return obj.get(ctorName, obj);
}
- public void setProperty(ScriptableObject obj, Object val) {
- obj.delete(ctorName);
- obj.put(ctorName, obj, val);
+ public Object setProperty(ScriptableObject obj, Object val) {
+ synchronized (obj) {
+ isReplaced = true;
+ return val;
+ }
}
private String ctorName;
private String className;
+ private boolean isReplaced;
}
Index: ScriptableObject.java
===================================================================
RCS file: /cvsroot/mozilla/js/rhino/org/mozilla/javascript/ScriptableObject.java,v
retrieving revision 1.17
diff -u -r1.17 ScriptableObject.java
--- ScriptableObject.java 2000/03/13 17:12:36 1.17
+++ ScriptableObject.java 2000/07/03 18:31:04
@@ -246,11 +246,21 @@
break;
}
}
- getterSlot.setter.invoke(start, arg);
+ Object v = getterSlot.setter.invoke(start, arg);
+ if (getterSlot.setterReturnsValue) {
+ slots[slotIndex].value = v;
+ if (!(v instanceof Method))
+ slots[slotIndex].flags = 0;
+ }
return;
}
Object[] args = { this, actualArg };
- getterSlot.setter.invoke(getterSlot.delegateTo, args);
+ Object v = getterSlot.setter.invoke(getterSlot.delegateTo, args);
+ if (getterSlot.setterReturnsValue) {
+ slots[slotIndex].value = v;
+ if (!(v instanceof Method))
+ slots[slotIndex].flags = 0;
+ }
return;
}
catch (InvocationTargetException e) {
@@ -1183,6 +1193,7 @@
slot.delegateTo = delegateTo;
slot.getter = getter;
slot.setter = setter;
+ slot.setterReturnsValue = setter != null && setter.getReturnType() !=
Void.TYPE;
slot.value = null;
slot.attributes = (short) attributes;
slot.flags = flags;
@@ -1551,6 +1562,7 @@
Object delegateTo; // OPT: merge with "value"
Method getter;
Method setter;
+ boolean setterReturnsValue;
}
Fergus Gallagher wrote:
> I am having problems getting my head around contexts and scopes and my
> multi-threaded application fall over.
>
> If I set "global=false" the following code used a per-thread
> initStandardObject() and this seems to work. But when I set
> "global=true", the global "parentScope" is used and I get some wierd
> errors.
>
> If I change "__CODE__.slice(0,5)" to
> 1. "__CODE__" - works
> 2. "__CODE__.substring(0,5)" - fails
> 3. "__CODE__.toString()" - works
>
> Any help appreciated.
>
> Fergus
>
> ===== Test.java =========================================
> import java.io.*;
> import org.mozilla.javascript.*;
>
> public class Test implements Runnable {
> private Script script;
> private Scriptable parentScope;
> private String __CODE__="ABCDEFGHIJK";
> private boolean global = true;
> private static Context globalContext = null;
> public Test() throws Exception {
> String js= "java.lang.System.out.println(__CODE__.slice(0,5));";
> globalContext.setCompileFunctionsWithDynamicScope(false);
> parentScope = globalContext.initStandardObjects(null);
> StringReader sr = new StringReader(js);
> script = globalContext.compileReader(parentScope, sr, "(compiled)",
> 1,null);
> }
>
> public void run() {
> try {
> Context context = Context.enter();
> Scriptable threadScope;
> if (global) {
> threadScope = context.newObject(parentScope);
> threadScope.setPrototype(parentScope);
> threadScope.setParentScope(null);
> } else {
> threadScope = context.initStandardObjects(null);
> }
> threadScope.put("__CODE__",threadScope,__CODE__);
> script.exec(context,threadScope);
> }
> catch (Exception e) {
> System.err.println(e.getClass().getName()+":
"+e.getMessage());
> }
> finally {
> Context.exit();
> }
> }
>
> public static void main(String args[]) throws Exception {
> globalContext = Context.enter();
> Test me = new Test();
> int count=10;
> Thread[] threads = new Thread[count];
> for (int i=0; i<count; i++) {
> Thread t = new Thread(me);
> threads[i] = t;
> t.start();
> }
> for (int i=0; i<count; i++) {
> threads[i].join();
> }
> Context.exit();
> }
> }
>
> ==== OUTPUT ===============================================
> ABCDE
> ABCDE
> org.mozilla.javascript.EcmaError: undefined is not a function.
> org.mozilla.javascript.EvaluatorException: Constructor for "String" not
> found.
> org.mozilla.javascript.EvaluatorException: Constructor for "String" not
> found.
> org.mozilla.javascript.EvaluatorException: Constructor for "String" not
> found.
> org.mozilla.javascript.EvaluatorException: Constructor for "String" not
> found.
> org.mozilla.javascript.EvaluatorException: Constructor for "String" not
> found.
> org.mozilla.javascript.EvaluatorException: Constructor for "String" not
> found.
> org.mozilla.javascript.EvaluatorException: Constructor for "String" not
> found.
> ===========================================================
>
> The number and type of exceptions is highly variable from run to run -
> anywhere from 1-9 out of 10.
> The EcmaError in particular only happens occasionally.
>
> --
> Fergus Gallagher Tel: +44 (20) 8 987 0717
> Orbis Fax: +44 (20) 8 742 2649
> The Swan Centre email: Fergus.Gallagher@orbisuk.com
> Fishers Lane Web: http://www.orbisuk.com
> London W4 1RX / UK
