c# - Why does the synchronized wrapper for ArrayList not work? -

-

i have generated proxy classes web service in vusual studio 'add web reference'. generated rtwebservice class has method setvalueasync. extended class , added setvaluerequest keeps track of requests , cancels pending requests when error occurs. every request store userstate object in arraylist created follows: 

requests = arraylist.synchronized(new arraylist());

i created method:

public void cancelpendingrequests() {   lock (requests.syncroot) {     if (requests.count > 0) {       foreach (object request in requests) {         this.cancelasync(request);       }       requests.clear();     }   } }

i call method when request returns on setvaluecompleted event:

private void onrequestcomplete(     object sender,      service.setvaluecompletedeventargs args ) {   lock (syncresponse) {     if (args.cancelled) {       return;     }      if (args.userstate != null) {       requests.remove(args.userstate);     }      if (args.error != null) {       cancelpendingrequests();     }   } }

to start new request call:

public void setvaluerequest(string tag, string value) {   var request = new object();   this.setvalueasync(tag, value, request);   requests.add(request); }

everytime make request , @ same time response returns error, targetinvocationexception in cancelpendingrequests. inner exception invalidoperationexception on arraylist in cancelpendingrequests method saying:

collection modified; enumeration operation may not execute.

so seems setvaluerequest has modified requests object while enumerating it. thought impossible because used synchronized wrapper arraylist , use syncroot synchronize enumeration. i'm bit stuck on if has idea?

  1. never use syncroot it's inherently broken. (if share list invite deadlock)

  2. don't use arraylist, should marked "deprecated".

  3. arraylist.synchronized return's works more not thread safe, i.e. it's not thread safe during set of operations.

  4. you can either use system.collection.concurrent, or use readerwriterlockslim


Comments

Post a Comment

Popular posts from this blog

javascript - Enclosure Memory Copies -

-
function myclass() { //lots , lots of vars , code here. this.bar = function() { //do numerous enclosed myclass vars } this.foo = function() { alert('hello'); //don't enclosed variables. } } each instance of myclass gets own copy of bar , foo, why prototyped methods use less memory. however, know more memory use of inner methods. it seems obvious me (1) below must true. agree? not distinct myclass instances have own distinct copies of bar, must have own distinct copies of myclass enclosure. (or else how bar method keep myclass variables straight on per instance basis?) now (2) question i'm after. since inner foo method doesn't use in myclass enclosure natural qustion is: javascript smart enough not keep myclass enclosure in memory use of foo? this depend entirely on implementation not language. naive implementations keep far more around others. answer true e.g. v8 (chrome's js engine) may not true spider...
Read more

php - Replacing tags in braces, even nested tags, with regex -

-
example preg_replace('/\{[a-za-z.,\(\)0-9]+\}/', 'replaced', 'lorem ipsum dolor sit {tag1({tag2()})}, consectetur adipiscing elit.'); the result: lorem ipsum dolor sit {tag1(replaced)}, consectetur adipiscing elit. question as can see "tag2" has been replaced, want replace "tag1" know how can this? (in cases might this: {tag1({tag2({tag3()})})}) , on.) btw using preg_replace_callback, easier show preg_replace here site can test code: http://www.spaweditor.com/scripts/regex/index.php you need add curly braces character set. here's pattern used: /\{[a-za-z.,\(\)\{\}0-9]+\}/ and here result: "lorem ipsum dolor sit replaced, consectetur adipiscing elit."
Read more