PHP multi-process debugging: Troubleshooting concurrent code

Question: How to debug multi-process programs in PHP? Tip: Use Xdebug for multi-process aware debugging. Set breakpoints and attach them to each process individually. Use the dbg:signal signal debugger to attach to the process in turn. Practical case: When debugging a multi-process web service, it was found that the response was always 404. By attaching to the process in turn, I discovered that RequestHandler was not loaded because the class was not in the autoload path. Updating composer.json and running composer update resolved the issue.

PHP Multi-Process Debugging: Troubleshooting Concurrent Code

Multiple processes are a powerful tool for executing tasks in parallel, but debugging concurrency Code can be challenging. This article introduces tips and practical cases for debugging multi-process programs in PHP to help you solve problems easily.

Using Xdebug

Xdebug is a PHP debugger that provides multi-process awareness, allowing you to debug parallel tasks. To use it, install the Xdebug extension and enable remote debugging mode.

/etc/php.ini
[xdebug]
xdebug.remote_enable = on
xdebug.remote_host = localhost

Set breakpoints

Similar to traditional single-process programs, you can set breakpoints in parallel code. In Xdebug, use the dbg:pid command to attaches to a specific process.

# 命令行
xhdb --eval 'echo dbg:pid()' | grep PID
# 此断点适用于进程 PID
xhdb --eval 'echo dbgp:meta(' . $PID . ')->breakpoint(' . $breakpoint . ')'

Practical case: Debugging a multi-process web service

Consider the following multi-process web server:

use Amp\Http\Server\HttpServer;
use Amp\Http\Server\RequestHandler;
use Amp\Http\Server\Response;
use Amp\Loop;

$server = new HttpServer(new RequestHandler());
Loop::run($server);

Problem: The response is always 404

Attach the signal debugger to the process in turn using the dbg:signal command:

xhdb --eval 'dbg:signal(SIGPROF + 5)' | grep PID

Then, access the web service and examine the stack trace in the Xdebug control panel .

Solution: Handler not found

The stack trace shows RequestHandler is not loaded. Through debugging, we found that the RequestHandler class is not in the autoloading path. Update composer.json and run composer update to resolve this issue.

Conclusion

By using Xdebug and targeted breakpoints, you can easily debug multi-process programs in PHP. A 404 error solved in a practical example demonstrates how to diagnose and resolve problems in parallel code.

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