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ASP.net session request queuing

It seems to me that ASP.net queues up all requests that use the same Session ID. Let's say you've got 3 pages.

Default.aspx

protected void Page_Load(object sender, EventArgs e)
{
    Session["asdf"] = "LOLZ";
}

Hitting this page would obviously create a new session if one doesn't exist.

X-AspNet-Version: 2.0.50727
Set-Cookie: ASP.NET_SessionId=ibjphuv0aiafqi453tyze345; path=/; HttpOnly

Then you hit Hang.aspx

protected void Page_Load(object sender, EventArgs e)
{
    Thread.Sleep(10000);
}

And immediately after you hit any other page that this session ID would be passed to, doesn't matter if it does anything, let's call it Test.aspx.

The sequence for loading is like so.

Request            Timeline
"GET /"            |*|
"GET /Hang.aspx"       |******************************************|
"GET /Test.aspx"            |**************************************|

I guess my question is how do I disable this feature. I understand it's useful to have so that session state can be more predictable, however in my case a long running reports page load is killing users' ability to multitask.

Concurrent and Blocking Queue in Java

I have the classic problem of a thread pushing events to the incoming queue of a second thread. Only this time, I am very interested about performance. What I want to achieve is:

• I want concurrent access to the queue, the producer pushing, the receiver poping.
• When the queue is empty, I wand the consumer to block to the queue, waiting for the producer.

My first idea was to use a LinkedBlockingQueue, but I soon realized that it is not concurrent and the performance suffered. On the other hand, I now use a ConcurrentLinkedQueue, but still I am paying the cost of wait()/notify() on each publication. Since the consumer, upon finding an empty queue, does not block, I have to synchronize and wait() on a lock. On the other part, the producer has to get that lock and notify() upon every single publication. The overall result is that I am paying the cost of sycnhronized (lock) {lock.notify()} in every single publication, even when not needed.

What I guess is needed here, is a queue that is both blocking and concurrent. I imagine a push() operation to work as in ConcurrentLinkedQueue, with an extra notify() to the object when the pushed element is the first in the list. Such a check I consider to already exist in the ConcurrentLinkedQueue, as pushing requires connecting with the next element. Thus, this would be much faster than synchronizing every time on the external lock.

Is something like this available/reasonable?

How do I write non-blocking code in Node.js?

I can write non-blocking I/O in Node.js very easily. It's what the entire library is set up for.

But any computation done is blocking. Any message passing over event emitters are blocking.

For example, emitting events are resolved immediately and are thus blocking:

var e = new process.EventEmitter;
e.on("foo", function() {
    console.log("event");
});
process.nextTick(function() {
    console.log("next tick");
});
setTimeout(function() {
    console.log("timeout");
}, 0);
e.emit("foo");

> event
> next tick
> timeout

Apart from wrapping calls in nextTick, how do I make code non-blocking?

I want to do as little computation per cycle of the event loop as possible, so that I can serve as many clients simultaneously as possible.

How do I write my code in a non-blocking fashion?

And when I have non-blocking code, how do I scale that across multiple processes?

One option is waiting for the WebWorker sub-process API to be finished.

How to create a sleep/delay in nodejs that is Blocking?

I'm currently trying to learn nodejs and a small project I'm working is writing an API to control some networked LED lights.

The microprocessor controlling the LEDs has a processing delay, and I need to space commands sent to the micro at least 100ms apart. In C# I'm used to just calling Thread.Sleep(time), but I have not found a similar feature in node.

I have found several solutions using the setTimeout(...) function in node, however, this is asynchronous and does not block the thread ( which is what I need in this scenario).

Is anyone aware of a blocking sleep or delay function? Preferably something that does not just spin the CPU, and has an accuracy of +-10 ms?

Event Loop vs Multithread blocking IO

I was reading a comment about server architecture.

http://news.ycombinator.com/item?id=520077

In this comment, the person says 3 things:

1. The event loop, time and again, has been shown to truly shine for a high number of low activity connections.
2. In comparison, a blocking IO model with threads or processes has been shown, time and again, to cut down latency on a per-request basis compared to an event loop.
3. On a lightly loaded system the difference is indistinguishable. Under load, most event loops choose to slow down, most blocking models choose to shed load.

Are any of these true?

And also another article here titled "Why Events Are A Bad Idea (for High-concurrency Servers)"

http://www.usenix.org/events/hotos03/tech/vonbehren.html

Twisted: Making code non-blocking

I'm a bit puzzled about how to write asynchronous code in python/twisted. Suppose (for arguments sake) I am exposing a function to the world that will take a number and return True/False if it is prime/non-prime, so it looks vaguely like this:

def IsPrime(numberin):
    for n in range(2,numberin):
        if numberin % n == 0: return(False)
    return(True)

(just to illustrate).

Now lets say there is a webserver which needs to call IsPrime based on a submitted value. This will take a long time for large numberin.

If in the meantime another user asks for the primality of a small number, is there a way to run the two function calls asynchronously using the reactor/deferreds architecture so that the result of the short calc gets returned before the result of the long calc?

I understand how to do this if the IsPrime functionality came from some other webserver to which my webserver would do a deferred getPage, but what if it's just a local function?

i.e., can Twisted somehow time-share between the two calls to IsPrime, or would that require an explicit invocation of a new thread?

Or, would the IsPrime loop need to be chunked into a series of smaller loops so that control can be passed back to the reactor rapidly?

Or something else?

asynchronous vs non-blocking

What is the difference between asynchronous and non-blocking calls? Also between blocking and synchronous calls (with examples please)?

How to prevent downloading images and video files from my website?

How to prevent downloading images and video files from my website? Is it possible? What would be the best way to do this?

What does InputStream.available() do in Java?

What does InputStream.available() do in Java? I read the documentation, but I still cannot make it out.

The doc says:

Returns the number of bytes that can be read (or skipped over) from this input stream without blocking by the next caller of a method for this input stream. The next caller might be the same thread or or another thread.

The available method for class InputStream always returns 0.

What do they mean by blocking? Does it just mean a synchronized call?

And most of all, what is the purpose of the available() method?

should LOCK_EX on both read & write be atomic?

file_put_contents ( "file", "data", LOCK_EX )

for writing (which means - aquire lock and write)

file_get_contents ( "file", LOCK_EX )

for reading (which means - aquire lock and then read)

will it throw exception? raise an error? block until lock is aquired? or at least - should it? is there a chance that php will behave like this one day?

EDIT: i know that it is possible to use rename - i'd like to know answer to this...

What does the term "blocking" mean in programming?

Could someone provide a layman definition and use case?

Blocking IO vs non-blocking IO; looking for good articles

Once upon a time I bumped into Introduction to Indy article and can't stop thinking about blocking vs non-blocking IO ever since then.

Looking for some good articles describing what are pros and cons of blocking IO and non-blocking IO and how to design your application in each case to get natural, easy to understand and easy to maintain code.
Would like to understand BIG picture...

Wrapping an asynchronous computation into a synchronous (blocking) computation

similar questions:

• Pattern for wrapping an Asynchronous JavaScript function to make it synchronous
• Wrapping an asynchronous method synchronously in C#

I have an object with a method I would like to expose to library clients (especially scripting clients) as something like:

interface MyNiceInterface
{
    public Baz doSomethingAndBlock(Foo fooArg, Bar barArg);
    public Future<Baz> doSomething(Foo fooArg, Bar barArg);
    // doSomethingAndBlock is the straightforward way;
    // doSomething has more control but deals with
    // a Future and that might be too much hassle for
    // scripting clients
}

but the primitive "stuff" I have available is a set of event-driven classes:

interface BazComputationSink
{
    public void onBazResult(Baz result);
}

class ImplementingThing
{
    public void doSomethingAsync(Foo fooArg, Bar barArg, BazComputationSink sink);
}

where ImplementingThing takes inputs, does some arcane stuff like enqueueing things on a task queue, and then later when a result occurs, sink.onBazResult() gets called on a thread that may or may not be the same thread as ImplementingThing.doSomethingAsync() was called.

Is there a way I can use the event-driven functions I have, along with concurrency primitives, to implement MyNiceInterface so scripting clients can happily wait on a blocking thread?

edit: can I use FutureTask for this?

Chrome blocking javascript on localhost

I'm working on developing a site on my local machine (Windows 7 Ultimate x64) using WAMP, running APACHE v2.2.22, PHP 5.3.13, and MySQL v5.5.24. I'm developing using Chrome v 22.0.1229.94. I've got quite a bit of javascript in the site, however, and Chrome is relentlessly blocking javascript from running on the page.

Clicking on the little 'blocked javascript on this page' icon in the address bar includes the dropdown that has "Always allow Javascript on Localhost" checked off, and I also have a JavaScript exception in Chrome's settings explicitly saying to always allow JavaScript on 'http://localhost'.

Cookies are being allowed, "Allow all sites to run JavaScript" is checked off, and I have no idea as to why Chrome is not allowing the JavaScript to run.

Overall, it's not imperative to the project that I figure out a fix as both IE9 and Firefox 16.1 are allowing JavaScript and I can utilize them. I am simply curious if there's anything I can do to fix this in Chrome, as I would like to continue developing in Chrome.

How would you implement a basic event-loop?

If you have worked with gui toolkits, you know that there is a event-loop/main-loop that should be executed after everything is done, and that will keep the application alive and responsive to different events. For example, for Qt, you would do this in main():

int main() {
    QApplication app(argc, argv);
    // init code
    return app.exec();
}

Which in this case, app.exec() is the application's main-loop.

The obvious way to implement this kind of loop would be:

void exec() {
    while (1) {
        process_events(); // create a thread for each new event (possibly?)
    }
}

But this caps the CPU to 100% and is practicaly useless. Now, how can I implement such an event loop that is responsive without eating the CPU altogether?

Answers are appreciated in Python and/or C++. Thanks.

Footnote: For the sake of learning, I will implement my own signals/slots, and I would use those to generate custom events (e.g. go_forward_event(steps)). But if you know how I can use system events manually, I would like to know about that too.