Introduction

In normal PHP web execution, you usually do not create a real background thread just to send an HTTP POST request. What people normally want is "fire and forget": send a request, stop waiting for the response, and let the main script continue.

There Usually Is No Real Thread Here

Classic PHP request handling is synchronous. Unless you are using a specialized runtime, you should assume one request is handled by one worker process or thread managed by the web server.

So the practical choices are:

• open a socket, write the HTTP request, and stop reading
• use an async HTTP client in a long-running PHP application
• queue the work instead of making an immediate HTTP callback

For most web applications, the queue option is the safest design.

A Minimal Fire-And-Forget Socket Example

If you only need to trigger another internal endpoint and do not care about the response body, a raw socket write is the simplest approach.

1<?php
2function fireAndForgetPost(string $host, int $port, string $path, array $payload): void
3{
4    $body = http_build_query($payload);
5    $fp = fsockopen($host, $port, $errno, $errstr, 2);
6
7    if (!$fp) {
8        error_log("Connection failed: $errstr ($errno)");
9        return;
10    }
11
12    $request = "POST $path HTTP/1.1\r\n";
13    $request .= "Host: $host\r\n";
14    $request .= "Content-Type: application/x-www-form-urlencoded\r\n";
15    $request .= "Content-Length: " . strlen($body) . "\r\n";
16    $request .= "Connection: Close\r\n\r\n";
17    $request .= $body;
18
19    fwrite($fp, $request);
20    fclose($fp);
21}
22
23fireAndForgetPost("127.0.0.1", 8080, "/hook", ["event" => "signup"]);

This does not guarantee the remote server finished processing the request. It only guarantees that your script attempted to send it.

When curl Is Not Enough

A lot of examples suggest curl_setopt($ch, CURLOPT_TIMEOUT_MS, 1). That is not a true fire-and-forget strategy. It usually just means your client gives up very quickly, possibly before the request is fully sent.

If you use curl, be honest about what it provides: asynchronous behavior for your script, not guaranteed delivery.

For reliable delivery, persist the work in a queue or database table and let a worker send it.

Finishing The HTTP Response First

Sometimes the actual goal is to answer the browser quickly and continue local work afterward. In PHP-FPM, fastcgi_finish_request() is useful for that case.

1<?php
2http_response_code(202);
3echo "Accepted";
4
5if (function_exists('fastcgi_finish_request')) {
6    fastcgi_finish_request();
7}
8
9// Continue background-like work after the client connection is closed.
10error_log('Processing webhook dispatch...');

This is not the same as creating a separate thread. It simply lets the client connection finish while the server-side PHP process keeps running briefly.

Queues Are Better For Important Work

If the POST request matters for billing, emails, audit logs, or cross-service workflows, do not rely on a fire-and-forget socket alone. Use a queue so you can retry failures and inspect what happened.

A better architecture is:

1. store a job record
2. return success or 202 Accepted
3. let a worker send the POST
4. retry on failure
5. log the result

That design is slower to build, but it is operationally correct.

Security And Networking Details

When sending to HTTPS endpoints, raw socket code becomes more complex because TLS validation matters. In those cases, a proper HTTP client or queue worker is usually the right tool.

Also be careful with internal callback loops. If your PHP app triggers an endpoint that triggers the same logic again, you can create accidental recursive traffic.

Common Pitfalls

The most common mistake is calling this "multithreading" in standard PHP. Usually it is just non-blocking or best-effort I/O.

Another mistake is assuming that closing the socket means the remote service definitely received and processed the POST. It might not have.

Developers also misuse tiny cURL timeouts and then wonder why requests disappear under load.

Finally, if the action matters to the business, avoid pure fire-and-forget. Use a queue, retries, and logging.

Summary

• Standard PHP usually does not create a separate thread for this task.
• A raw socket write can approximate fire-and-forget behavior.
• Very short cURL timeouts are not a reliable delivery mechanism.
• 'fastcgi_finish_request() is useful when you want to respond first and continue local work.'
• For important workflows, queue the job instead of relying on best-effort HTTP dispatch.