The answer is epoll if you&#39;re using Linux, kqueue if you&#39;re using FreeBSD or Mac OS X, and i/o completion ports if you&#39;re on Windows.

Some additional things you&#39;ll (almost certainly) want to research are:

- Load balancing techniques
- Multi-threaded networking
- Database architecture
- Perfect hash tables

Additionally, it is **important** to note that UDP does not have &quot;connections&quot; as opposed to TCP. It would also be in your best interest to start small and scale larger since debugging network-based solutions can be challenging.

The author of CURL wrote an amazing article on **[poll vs select vs event libraries][1]**.


  [1]: https://daniel.haxx.se/docs/poll-vs-select.html

Linux: `epoll`
FreeBSD: `kqueue`
Windows: ??

There are wrapper libraries, such as libevent and libev, which can abstract this for you.

It&#39;s possible to bind more than one signal to one slot (isn&#39;t?). So, is there a way to understand which widget sends the signal? I&#39;m looking for something like `sender` argument of events in .NET

How to get sender widget with a signal/slot mechanism?

Given the code below, what is the difference between the way `position0` is initialized and the way `position1` is initialized?  Are they equivalent?  If not, what is the difference?

    class Program
    {
        static void Main(string[] args)
        {
            Position position0 = new Position() { x=3, y=4 };

            Position position1 = new Position();
            position1.x = 3;
            position1.y = 4;
        }
    }

    struct Position
    {
        public int x, y;
    }

What do braces after C# new statement do?

I am designing a new server which needs to support thousands of UDP connections (somewhere around 100,000 sessions). Any input or suggestions on which one to use?


select vs poll vs epoll

<p>I am designing a new server which needs to support thousands of UDP connections (somewhere around 100,000 sessions). Any input or suggestions on which one to use?</p>


When should we use mutex and when should we use semaphore ?


When should we use mutex and when should we use semaphore

On POSIX systems, termination signals usually have the following order (according to many MAN pages and the POSIX Spec):

 1. SIGTERM - politely ask a process to terminate. It shall terminate gracefully, cleaning up all resources (files, sockets, child processes, etc.), deleting temporary files and so on.

 2. SIGQUIT - more forceful request. It shall terminate ungraceful, still cleaning up resources that absolutely need cleanup, but maybe not delete temporary files, maybe write debug information somewhere; on some system also a core dump will be written (regardless if the signal is caught by the app or not).

 3. SIGKILL - most forceful request. The process is not even asked to do anything, but the system will clean up the process, whether it like that or not. Most likely a core dump is written.

How does SIGINT fit into that picture? A CLI process is usually terminated by SIGINT when the user hits CRTL+C, however a background process can also be terminated by SIGINT using KILL utility. What I cannot see in the specs or the header files is if SIGINT is more or less forceful than SIGTERM or if there is any difference between SIGINT and SIGTERM at all.

**UPDATE:**

The best description of termination signals I found so far is in the [GNU LibC Documentation][1]. It explains very well that there is an intended difference between SIGTERM and SIGQUIT. 

It says about SIGTERM:

&gt; It is the normal way to politely ask a program to terminate. 

And it says about SIGQUIT:

&gt; [...] and produces a core dump when it terminates the process, just like a program error signal.
&gt; You can think of this as a program error condition “detected” by the user. [...] 
&gt; Certain kinds of cleanups are best omitted in handling SIGQUIT. For example, if the program 
&gt; creates temporary files, it should handle the other termination requests by deleting the temporary 
&gt; files. But it is better for SIGQUIT not to delete them, so that the user can examine them in 
&gt; conjunction with the core dump.

And SIGHUP is also explained well enough. SIGHUP is not really a termination signal, it just means the &quot;connection&quot; to the user has been lost, so the app cannot expect the user to read any further output (e.g. stdout/stderr output) and there is no input to expect from the user any longer. For most apps that mean they better quit. In theory an app could also decide that it goes into daemon mode when a SIGHUP is received and now runs as a background process, writing output to a configured log file. For most daemons already running in the background, SIGHUP usually means that they shall reexamine their configuration files, so you send it to background processes after editing config files.

However there is no useful explanation of SIGINT on this page, other than that it is sent by CRTL+C. Is there any reason why one would handle SIGINT in a different way than SIGTERM? If so what reason would this be and how would the handling be different?

  [1]: http://www.gnu.org/s/libc/manual/html_node/Termination-Signals.html

How does SIGINT relate to the other termination signals such as SIGTERM, SIGQUIT and SIGKILL?

I used `strace` to attach to a process briefly. The process created 90 threads. When I found the offending thread, I had to tediously search for the parent thread, then the grandparent thread, and so on all the way to the root process.

Is there a trick or tool to quickly figure out which thread created another? Or better yet, print the tree of thread creations like `pstree`? 


How to track child process using strace?

I want to run a shell script when a specific file or directory changes.

How can I easily do that?

How to run a shell script when a file or directory changes?

I want to create a clone of the structure of our multi-terabyte file server.  I know that cp --parents can move a file and it&#39;s parent structure, but is there any way to copy the directory structure intact? 

I want to copy to a linux system and our file server is CIFS mounted there.

Copy folder structure (without files) from one location to another

What does EAGAIN mean?

In C, I understood that if we close a socket, it means the socket will be destroyed and can be re-used later.

How about shutdown? The description said it closes half of a duplex connection to that socket. But will that socket be destroyed like `close` system call? 



close vs shutdown socket?

I&#39;m writing a simple program that makes multiple connections to different servers for status check. All these connections are constructed on-demand; up to 10 connections can be created simultaneously. I don&#39;t like the idea of one-thread-per-socket, so I made all these client sockets Non-Blocking, and throw them into a select() pool.

It worked great, until my client complained that the waiting time is too long before they can get the error report when target servers stopped responding.

I&#39;ve checked several topics in the forum. Some had suggested that one can use alarm() signal or set a timeout in the select() function call. But I&#39;m dealing with multiple connections, instead of one. When a process wide timeout signal happens, I&#39;ve no way to distinguish the timeout connection among all the other connections.

Is there anyway to change the system-default timeout duration ? 

How to set socket timeout in C when making multiple connections?

Is there any way to use Socket.IO http://socket.io/ with Django?

Can I use Socket.IO with Django?

In the context of Java, I create a new thread to read network input when open a GUI window, and when i close the window, i want to release the socket resource and terminate the thread immediately. Now i am using setSoTimeout method, but i don&#39;t want to wait the timeout exception. Could anybody give some suggestion? Thanks!

How to terminate a thread blocking on socket IO operation instantly?

Could someone explain what the difference is between `epoll`, `poll` and threadpool?

- What are the pros / cons?
- Any suggestions for frameworks?
- Any suggestions for simple/basic tutorials?
- It seems that `epoll` and `poll` are Linux-specific... Is there an equivalent alternative for Windows?


What&#39;s the difference between epoll, poll, threadpool?

Event-driven and asynchronous are often used as synonyms. Are there any differences between the two?

Also, what is the difference between `epoll` and `aio`? How do they fit together?

Lastly, I&#39;ve read many times that AIO in Linux is horribly broken. How exactly is it broken?

Thanks.

What&#39;s the difference between event-driven and asynchronous? Between epoll and AIO?

Wikipedia says 

&gt; unlike the older system calls, which
&gt; operate at O(n), epoll operates in
&gt; O(1) [2]).

http://en.wikipedia.org/wiki/Epoll


However, the source code at fs/eventpoll.c on Linux-2.6.38,
seems it is implemented with an RB tree for searching, which has O(logN)

    /*
     * Search the file inside the eventpoll tree. The RB tree operations
     * are protected by the &quot;mtx&quot; mutex, and ep_find() must be called with
     * &quot;mtx&quot; held.
     */
    static struct epitem *ep_find(struct eventpoll *ep, struct file *file, int fd)
    {


In fact, I couldn&#39;t see any man page saying the complexity of epoll() is O(1).
Why is it known as O(1)?




Does epoll(), do its job in O(1)?

From epoll&#39;s man page:

    epoll is a variant of poll(2) that can be used either as an edge-triggered
    or a level-triggered interface
When would one use the edge triggered option? The man page gives an example that uses it, but I don&#39;t see why it is necessary in the example.

What is the purpose of epoll&#39;s edge triggered option?

I have seen a lot of comparisons which says select have to walk through the fd list, and this is slow. But why doesn&#39;t epoll have to do this?

Content Type	Original Author	Original Content on Stackoverflow
Question	ravi	View Question on Stackoverflow
Solution 1 - Linux	Kalantir	View Answer on Stackoverflow
Solution 2 - Linux	unixman83	View Answer on Stackoverflow
Solution 3 - Linux	Yann Ramin	View Answer on Stackoverflow

select vs poll vs epoll

Linux Problem Overview

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What do braces after C# new statement do?

How to get sender widget with a signal/slot mechanism?

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