I know gettext and [set_locale][1] is not threadsafe. PHP should not be used with a threaded MPM.

[PHP Isn&#39;t Thread-Safe Yet][2].  
[Running PHP not threaded][3].


  [1]: http://php.net/manual/en/function.setlocale.php
  [2]: http://neosmart.net/blog/2008/dont-believe-the-lies-php-isnt-thread-safe-yet/
  [3]: https://stackoverflow.com/questions/1646249/php-gettext-problems-like-non-thread-safe/6726570#6726570

See *[Where can I get libraries needed to compile some of the optional PHP extensions?][1]* for a list of thread-safe and nonthread-safe extensions (* marked are not thread-safe and others are).

  [1]: http://php.net/manual/en/faq.obtaining.php#faq.obtaining.optional

A better question might be, &quot;Is the following PHP code going to trigger access violations if MPM is used?&quot; Or, &quot;Have you experienced odd behavior likely attributed to concurrency issues using the following functions?&quot;

Otherwise, it&#39;s Russian roulette. If you&#39;re using some packaged application, it may work just fine now but break a month from now when a new version of the application comes out.

I strongly advise against using MPM with PHP in general. However, if you have some small code to run, you could post it, and we could tell you if you&#39;re going to hit a pitfall.

So I keep hearing that PreparedStatements are good for performance.

We have a Java application in which we use the regular &#39;Statement&#39; more than we use the &#39;PreparedStatement&#39;. While trying to move towards using more PreparedStatements, I am trying to get a more thorough understanding of how PreparedStatements work - on the client side and the server side.

So if we have some typical CRUD operations and update an object repeatedly in the application, does it help to use a PS? I understand that we will have to close the PS every time otherwise it will result in a cursor leak.

So how does it help with performance? Does the driver cache the precompiled statement and give me a copy the next time I do connection.prepareStatement? Or does the DB server help? 

I understand the argument about the security benefits of PreparedStatements and I appreciate the answers below which emphasize it. However I really want to keep this discussion focused on the performance benefits of PreparedStatements.

Update: When I say update data, I really mean more in terms of that method randomly being called several times. I understand the advantage in the answer offered below which asks to re-use the statement inside a loop.
   
   

        // some code blah blah
        update();

        // some more code blah blah 
        update();

    .... 

    public void update () throws SQLException{
     try{
          PreparedStatement ps = connection.prepareStatement(&quot;some sql&quot;);
          ps.setString(1, &quot;foobar1&quot;);
          ps.setString(2, &quot;foobar2&quot;);
          ps.execute();
     }finally {
         ps.close();
         
     }

    }
    


There is no way to actually reuse the &#39;ps&#39; java object and I understand that the actual connection.prepareStatement call is quite expensive. 

Which is what brings me back to the original question. Is this &quot;some sql&quot; PreparedStatement still being cached and reused under the covers that I dont know about?

I should also mention that we support several databases.

Thanks in advance.

PreparedStatements and performance

Every once in a while I want to replace all instances of values like:

    &lt;BarFoo&gt;

with

    &lt;barfoo&gt;

i.e. do a regular expression replace of all things inside angle brackets with its lowercase equivalent.

Anyone got a nice snippet of Lisp that does this? It&#39;s safe to assume that we&#39;re dealing with just ASCII values. Bonus points for anything that is generic enough to take a full regular expression, and doesn&#39;t just handle the angle brackets example. Even more bonus points to an answer which just uses `M-x query-replace-regexp`.

Thanks,

Dom

Emacs: regular expression replacing to change case

- **Is PHP (as of 5.2) thread-safe on Linux/UNIX?**
- **Would it be possible to use it with Apache Worker-MPM or Event-MPM?**

The facts I gathered so far are inconclusive:

- Default binaries included in most distributions have ZTS disabled, so I&#39;m aware, that I&#39;d have to recompile them.
- In theory Zend Engine (core PHP) with ZTS enabled is thread-safe.
- It&#39;s said that some modules might not be thread-safe, but I haven&#39;t found any list of modules that are or that are not.
- [PHP FAQ][1] states pretty much same as above.

What&#39;s your experience?

It&#39;s not only about [segmentation faults][2] (&quot;access violations&quot; in Windows nomenclature). There is a lot more to [thread safety][3].

  [1]: http://www.php.net/manual/en/faq.installation.php#faq.installation.apache2
  [2]: http://en.wikipedia.org/wiki/Segmentation_fault
  [3]: http://en.wikipedia.org/wiki/Thread_safe


Is PHP thread-safe?

<ul>
<li>Is PHP (as of 5.2) thread-safe on Linux/UNIX?</li>
<li>Would it be possible to use it with Apache Worker-MPM or Event-MPM?</li>
</ul>
The facts I gathered so far are inconclusive:
<ul>
<li>Default binaries included in most distributions have ZTS disabled, so I'm aware, that I'd have to recompile them.</li>
<li>In theory Zend Engine (core PHP) with ZTS enabled is thread-safe.</li>
<li>It's said that some modules might not be thread-safe, but I haven't found any list of modules that are or that are not.</li>
<li><a href="http://www.php.net/manual/en/faq.installation.php#faq.installation.apache2" target="_blank" rel="noopener noreferrer">PHP FAQ</a> states pretty much same as above.</li>
</ul>
What's your experience?
It's not only about <a href="http://en.wikipedia.org/wiki/Segmentation_fault" target="_blank" rel="noopener noreferrer">segmentation faults</a> ("access violations" in Windows nomenclature). There is a lot more to <a href="http://en.wikipedia.org/wiki/Thread_safe" target="_blank" rel="noopener noreferrer">thread safety</a>.

I have a PHP script that&#39;s being called through jQuery AJAX. I want the PHP script to return the data in JSON format to the javascript. Here&#39;s the pseudo code in the PHP script:

    $json = &quot;{&quot;;
    foreach($result as $addr)
    {
    	foreach($addr as $line)
    	{
    		$json .= $line . &quot;\n&quot;;
    	}
    	$json .= &quot;\n\n&quot;;
    }
    $json .= &quot;}&quot;;

Basically, I need the results of the two for loops to be inserted in $json.

Returning JSON from PHP to JavaScript?

When I want to remove a Cookie I try

    unset($_COOKIE[&#39;hello&#39;]);

I see in my cookie browser from firefox that the cookie still exists. How can I really remove the cookie?

Remove a cookie

There is a strange behaviour with `json_encode` and `json_decode` and I can&#39;t find a solution:

My php application calls a php web service. The webservice returns json that looks like this: 

    var_dump($foo):
    string(62) &quot;{&quot;action&quot;:&quot;set&quot;,&quot;user&quot;:&quot;123123123123&quot;,&quot;status&quot;:&quot;OK&quot;}&quot;

now I like to decode the json in my application:

    $data = json_decode($foo, true)

but it returns `NULL`:

    var_dump($data):
    NULL

I use php5. 
The Content-Type of the response from the webservice: `&quot;text/html; charset=utf-8&quot;` (also tried to use `&quot;application/json; charset=utf-8&quot;`)

What could be the reason?






json_decode returns NULL after webservice call

I have a friendly argument going on with a co-worker about this, and my personal opinion is that a ASP.NET-MVC compiled web application would run more efficiently/faster than the same project that would be written in PHP.  My friend disagrees.

Unfortunately I do not have any solid data that I can use to back up my argument. (neither does he)

To this, I tried to Google for answers to try and find evidence to prove him wrong but most of the time the debate turned into which platform it is better to develop on, cost, security features, etc... For the sake of this argument I really don&#39;t care about any of that.

I would like to know what stack overflow community thinks about the raw speed/efficency of websites in general that are developed in ASP.NET with MVC versus exactly the same website developed with PHP?

Does anyone have any practical examples in real-world scenarios comparing the performance of the two technologies?

*(I realize for some of you this may very well be an irrelevant and maybe stupid argument, but it is an argument, and I would still like to hear the answers of the fine people here at S.O.)*



Speed of code execution: ASP.NET-MVC versus PHP

I have this code:

    private static $dates = array(
      &#39;start&#39; =&gt; mktime( 0,  0,  0,  7, 30, 2009),  // Start date
      &#39;end&#39;   =&gt; mktime( 0,  0,  0,  8,  2, 2009),  // End date
      &#39;close&#39; =&gt; mktime(23, 59, 59,  7, 20, 2009),  // Date when registration closes
      &#39;early&#39; =&gt; mktime( 0,  0,  0,  3, 19, 2009),  // Date when early bird discount ends
    );

Which gives me the following error:

&gt;Parse error: syntax error, unexpected &#39;(&#39;, expecting &#39;)&#39; in /home/user/Sites/site/registration/inc/registration.class.inc on line 19

So, I guess I am doing something wrong... but how can I do this if not like that? If I change the mktime stuff with regular strings, it works. So I know that I can do it *sort of* like that..

Anyone have some pointers?

How to initialize static variables

I have an object with a method named `StartDownload()`, that starts three threads.

How do I get a notification when each thread has finished executing?

Is there a way to know if one (or all) of the thread is finished or is still executing?

How to know if other threads have finished?

I&#39;m reading a c# book that describes the SyncRoot pattern. It shows

    void doThis()
    {
        lock(this){ ... }
    }

    void doThat()
    {
        lock(this){ ... }
    }

and compares to the SyncRoot pattern:

    object syncRoot = new object();

    void doThis()
    {
        lock(syncRoot ){ ... }
    }

    void doThat()
    {
        lock(syncRoot){ ... }
    }

However, I don&#39;t really understand the difference here; it seems that in both cases both methods can only be accessed by one thread at a time. 

The book describes *... because the object of the instance can also be used for synchronized access from the outside and you can&#39;t control this form the class itself, you can use the SyncRoot pattern* Eh? &#39;object of the instance&#39;?

Can anyone tell me the difference between the two approaches above? 

What&#39;s the use of the SyncRoot pattern?

How many threads can a Java VM support? Does this vary by vendor? by operating system? other factors?

How many threads can a Java VM support?

What is mutex and semaphore in Java ? What is the main difference ?

What is mutex and semaphore in Java ? What is the main difference?

**UPDATE**

As of C# 6, [the answer][1] to this question is:

    SomeEvent?.Invoke(this, e);

----

I frequently hear/read the following advice:

Always make a copy of an event before you check it for `null` and fire it. This will eliminate a potential problem with threading where the event becomes `null` at the location right between where you check for null and where you fire the event:

    // Copy the event delegate before checking/calling
    EventHandler copy = TheEvent;

    if (copy != null)
        copy(this, EventArgs.Empty); // Call any handlers on the copied list

*Updated*: I thought from reading about optimizations that this might also require the event member to be volatile, but Jon Skeet states in his answer that the CLR doesn&#39;t optimize away the copy.

But meanwhile, in order for this issue to even occur, another thread must have done something like this:

    // Better delist from event - don&#39;t want our handler called from now on:
    otherObject.TheEvent -= OnTheEvent;
    // Good, now we can be certain that OnTheEvent will not run...

The actual sequence might be this mixture:

    // Copy the event delegate before checking/calling
    EventHandler copy = TheEvent;

    // Better delist from event - don&#39;t want our handler called from now on:
    otherObject.TheEvent -= OnTheEvent;    
    // Good, now we can be certain that OnTheEvent will not run...

    if (copy != null)
        copy(this, EventArgs.Empty); // Call any handlers on the copied list

The point being that `OnTheEvent` runs after the author has unsubscribed, and yet they just unsubscribed specifically to avoid that happening. Surely what is really needed is a custom event implementation with appropriate synchronisation in the `add` and `remove` accessors. And in addition there is the problem of possible deadlocks if a lock is held while an event is fired.

So is this [Cargo Cult Programming][2]? It seems that way - a lot of people must be taking this step to protect their code from multiple threads, when in reality it seems to me that events require much more care than this before they can be used as part of a multi-threaded design. Consequently, people who are not taking that additional care might as well ignore this advice - it simply isn&#39;t an issue for single-threaded programs, and in fact, given the absence of `volatile` in most online example code, the advice may be having no effect at all.

(And isn&#39;t it a lot simpler to just assign the empty `delegate { }` on the member declaration so that you never need to check for `null` in the first place?)

*Updated:* In case it wasn&#39;t clear, I did grasp the intention of the advice - to avoid a null reference exception under all circumstances. My point is that this particular null reference exception can only occur if another thread is delisting from the event, and the only reason for doing that is to ensure that no further calls will be received via that event, which clearly is NOT achieved by this technique. You&#39;d be concealing a race condition - it would be better to reveal it! That null exception helps to detect an abuse of your component. If you want your component to be protected from abuse, you could follow the example of WPF - store the thread ID in your constructor and then throw an exception if another thread tries to interact directly with your component. Or else implement a truly thread-safe component (not an easy task).

So I contend that merely doing this copy/check idiom is cargo cult programming, adding mess and noise to your code. To actually protect against other threads requires a lot more work.

**Update in response to Eric Lippert&#39;s blog posts:**

So there&#39;s a major thing I&#39;d missed about event handlers: &quot;event handlers are required to be robust in the face of being called even after the event has been unsubscribed&quot;, and obviously therefore we only need to care about the possibility of the event delegate being `null`. *Is that requirement on event handlers documented anywhere?*

And so: &quot;There are other ways to solve this problem; for example, initializing the handler to have an empty action that is never removed. But doing a null check is the standard pattern.&quot;

So the one remaining fragment of my question is, *why is explicit-null-check the &quot;standard pattern&quot;?* The alternative, assigning the empty delegate, requires only `= delegate {}` to be added to the event declaration, and this eliminates those little piles of stinky ceremony from every place where the event is raised. It would be easy to make sure that the empty delegate is cheap to instantiate. Or am I still missing something?

Surely it must be that (as Jon Skeet suggested) this is just .NET 1.x advice that hasn&#39;t died out, as it should have done in 2005?


  [1]: https://stackoverflow.com/a/45949862/3195477
  [2]: http://en.wikipedia.org/wiki/Cargo_cult_programming

C# Events and Thread Safety

I need a queue which multiple threads can put stuff into, and multiple threads may read from.

Python has at least two queue classes, `Queue.Queue` and `collections.deque`, with the former seemingly using the latter internally. Both claim to be thread-safe in the documentation.

However, the Queue docs also state:

&gt; collections.deque is an alternative
&gt; implementation of unbounded queues
&gt; with fast atomic append() and
&gt; popleft() operations **that do not
&gt; require locking.**

Which I guess I don&#39;t quite unterstand: Does this mean deque isn&#39;t fully thread-safe after all?

If it is, I may not fully understand the difference between the two classes. I can see that Queue adds blocking functionality. On the other hand, it loses some deque features like support for the in-operator.

Accessing the internal deque object directly, is

&gt; x in Queue().deque

thread-safe?

Also, **why does Queue employ a mutex for it&#39;s operations when deque is thread-safe already?**

Queue.Queue vs. collections.deque

Is malloc thread-safe?

Recently, I asked a question, with title as [&quot;Is malloc thread safe?&quot;][1], and inside that I asked, &quot;Is malloc re-entrant?&quot;

I was under the impression that all re-entrant are thread-safe.

Is this assumption wrong?


  [1]: https://stackoverflow.com/questions/855763/malloc-thread-safe

Threadsafe vs re-entrant

In the example code

    void foo()
    {
      static Bar b;
      ...
    }

compiled with **GCC** is it guaranteed that `b` will be created and initialized in a thread-safe manner ?

In gcc&#39;s man page, found the **-fno-threadsafe-statics** command line option:

&gt; Do not emit the extra code to use the
&gt; routines specified in the C++ ABI for
&gt; thread-safe initialization of local
&gt; statics. You can use this option to
&gt; reduce code size slightly in code that
&gt; doesn&#39;t need to be thread-safe.

1. Does it mean, that local statics are thread-safe by default with GCC ? So no reason to put explicit guarding e.g. with `pthread_mutex_lock/unlock` ?

2. How to write portable code - how to check if compiler will add its guards ? Or is it better to turn off this feature of GCC ?

Are function static variables thread-safe in GCC?

In particular 

 1. Create a function to take an array and an index as parameters.
 2. Create a n element array.
 3. Create a n count loop.
 4. Inside the loop on a new thread assign a new instance of the object to the array using the indexer passed in. 

I know how to manage the threads etc. I am interested in know if this is thread safe way of doing something.
 

     class Program
    {
        // bogus object
        class SomeObject
        {
            private int value1;
            private int value2;

            public SomeObject(int value1, int value2)
            {
                this.value1 = value1;
                this.value2 = value2;
            }
        }
       
        static void Main(string[] args)
        {

            var s = new SomeObject[10];
            var threads = Environment.ProcessorCount - 1;
            var stp = new SmartThreadPool(1000, threads, threads);
            for (var i = 0; i &lt; 10; i++)
            {
                stp.QueueWorkItem(CreateElement, s, i);
            }

        }

        static void CreateElement(SomeObject[] s, int index)
        {
            s[index] = new SomeObject(index, 2);
        }
    }

Content Type	Original Author	Original Content on Stackoverflow
Question	vartec	View Question on Stackoverflow
Solution 1 - Php	OIS	View Answer on Stackoverflow
Solution 2 - Php	AbdolHosein	View Answer on Stackoverflow
Solution 3 - Php	Tim Post	View Answer on Stackoverflow

Is PHP thread-safe?

Php Problem Overview

Php Solutions

Solution 1 - Php

Solution 2 - Php

Solution 3 - Php

Emacs: regular expression replacing to change case

PreparedStatements and performance

Attributions