This is a feature of Windows. It keeps network connections open for a long time by default.

You could either work around this by "Adjust the MaxUserPort and TcpTimedWaitDelay settings" - 
https://docs.microsoft.com/en-us/biztalk/technical-guides/settings-that-can-be-modified-to-improve-network-performance

Or you can re-use the same Curl object, which will almost certainly re-use the underlying network connection if possible, 

```
$ch = curl_init($url);

for($i = 0; $i < 5000; $i++)
{
    curl_setopt($ch, CURLOPT_URL, $url);
    $response = curl_exec($ch);
}

curl_close($ch);
```

I'll leave it open, so that someone who is more sure that there is nothing to be done in PHP, can close it.

I think @danack is spot on.  But instead of fiddling with these
Windows settings, I suggest to re-use the same curl resource
(object as of PHP 8.0.0), like described by Dan, to avoid calling
curl_easy_cleanup() under the hood, because[1]

| re-using handles is a key to good performance with libcurl

Anyway, this is not a PHP issue.

[1] <https://curl.se/libcurl/c/curl_easy_cleanup.html>

First thanks for the quick response.

What is not clear for me, is why the connection I open to the external server can be closed immediately and why this local local port connections, which i do not have if i use curl from command line, are still open even if the external connection I open is closed.

Because each connection is opened in a different thread i think I can not reuse them.

it's just how TCP works

https://superuser.com/questions/173535/what-are-close-wait-and-time-wait-states

Thank you @danack and @cmb for the quick response.

Your suggestions with reusing the the curl handle is correct if you're using a cli application and you're in control of the environment.
The problem described by Maik is that if you're using apache you can't reuse curl handles.

@rtrtrtrtrt, your comment is unfortunately not helping in this topic ;-)
The key question is, why is the mass usage of curl.exe not causing TIME_WAITs and the php libcurl functions causing TIME_WAITs. Furthermore the php functinos are not causing TIME_WAITs to the called server as one would expect, but it's causing TIME_WAITs for some kind of local redirects. It's causing localhost to localhost TIME_WAITs.

To clarify: you are not initializing multiple curl handles in a
single request, but rather for different requests, and you are
using the apache2handler SAPI?

In this case there may indeed be a problem, since the SAPI
intializes libcurl (curl_global_init()) at its startup and shuts
it down (curl_global_cleanup()) at its shutdown, so libcurl might
keep connections open, but may not reuse them.

> It's causing localhost to localhost TIME_WAITs.

Frankly, I have no idea why that happens.  The curl extension is
relatively thin wrapper around libcurl, so I wonder whether we set
up or use libcurl inappropriately, or whether Apache or the SAPI
interferes.

Hello,

yes we are using apache2handler SAPI and each request initializes a curl handle.

But also if I'm initialize a curl handle in a cli application and close it the connection I openend is closed but the corresponding local to local port connection, which i have not explicit opened, stays in TIME_WAIT.

When I'm opening and close the same connection with curl from command line without PHP i can not see such a local to local port connection.

Thanks for the support.

PHP 7.4 is out of active support; is this still an issue for you
with PHP 8.0 or 8.1?

No feedback was provided. The bug is being suspended because
we assume that you are no longer experiencing the problem.
If this is not the case and you are able to provide the
information that was requested earlier, please do so and
change the status of the bug back to "Re-Opened". Thank you.