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# IV. Advanced PHP debugger

# Introduction

APD is the Advanced PHP Debugger. It was written to provide profiling and debugging capabilities for PHP code, as well as to provide the ability to print out a full stack backtrace. APD supports interactive debugging, but by default it writes data to trace files. It also offers event based logging so that varying levels of information (including function calls, arguments passed, timings, etc.) can be turned on or off for individual scripts.

Caution
APD is a Zend Extension, modifying the way the internals of PHP handle function calls, and thus may or may not be compatible with other Zend Extensions (for example Zend Optimizer).

# Installation

APD is currently available as a PECL extension from http://pecl.php.net/package/apd. Make sure you have installed the CGI version of PHP and it is available in your current path along with the phpize script.

Run the following command to download, build, and install the latest stable version of APD:

    pear install apd

This automatically installs the APD Zend module into your PHP extensions directory. It is not mandatory to keep it there; you can store the module in any directory PHP can read as long as you set the zend_extension parameter accordingly.

Windows users can download the extension dll `php_apd.dll` from http://snaps.php.net/win32/PECL_STABLE/.

In your INI file, add the following lines:

    zend_extension = /absolute/path/to/apd.so
    apd.dumpdir = /absolute/path/to/trace/directory
    apd.statement_tracing = 0

Depending on your PHP build, the zend_extension directive can be one of the following:

    zend_extension              (non ZTS, non debug build)
    zend_extension_ts           (    ZTS, non debug build)
    zend_extension_debug        (non ZTS,     debug build)
    zend_extension_debug_ts     (    ZTS,     debug build)

# Building on Win32

To build APD under Windows you need a working PHP compilation environment as described on http://php.net/ -- basically, it requires you to have Microsoft Visual C++, win32build.zip, bison/flex, and some know how to get it to work. Also ensure that adp.dsp has DOS line endings; if it has unix line endings, Microsoft Visual C++ will complain about it.

# Runtime Configuration

The behaviour of these functions is affected by settings in `php.ini`.

Table 1. APD Configuration Options

Name | Default | Changeable | Changelog
--- | --- | --- | ---
apd.dumpdir | NULL | PHP_INI_ALL |
apd.statement_tracing | "0" | PHP_INI_ALL |

For further details and definitions of the PHP_INI_* constants, see the Appendix G.

Here's a short explanation of the configuration directives.

apd.dumpdir string

  Sets the directory in which APD writes profile dump files. You can specify an absolute path or a relative path.

  You can specify a different directory as an argument to apd_set_pprof_trace().

apd.statement_tracing boolean

  Specfies whether or not to do per-line tracings. Turning this on (1) will impact the performance of your application.

# Resource Types

This extension has no resource types defined.

# Predefined Constants

This extension has no constants defined.

# How to use PHP-APD in your scripts

1. As the first line of your PHP script, call the apd_set_pprof_trace() function to start the trace:

   `apd_set_pprof_trace();`

   You can insert the line anywhere in your script, but if you do not start tracing at the beginning of your script you discard profile data that might otherwise lead you to a performance bottleneck.

2. Now run your script. The dump output will be written to `apd.dumpdir/pprof_pid.ext`.

   > Tip: If you're running the CGI version of PHP, you will need to add the '-e' flag to enable extended information for apd to work properly. For example: `php -e -f script.php`

3. To display formatted profile data, issue the pprofp command with the sort and display options of your choice. The formatted output will look something like:

       bash-2.05b$ pprofp -R /tmp/pprof.22141.0

       Trace for /home/dan/testapd.php
       Total Elapsed Time = 0.00
       Total System Time  = 0.00
       Total User Time    = 0.00

       Real         User        System             secs/    cumm
       %Time (excl/cumm)  (excl/cumm)  (excl/cumm) Calls    call    s/call  Memory Usage Name
       --------------------------------------------------------------------------------------
       100.0 0.00 0.00  0.00 0.00  0.00 0.00     1  0.0000   0.0009            0 main
       56.9 0.00 0.00  0.00 0.00  0.00 0.00     1  0.0005   0.0005            0 apd_set_pprof_trace
       28.0 0.00 0.00  0.00 0.00  0.00 0.00    10  0.0000   0.0000            0 preg_replace
       14.3 0.00 0.00  0.00 0.00  0.00 0.00    10  0.0000   0.0000            0 str_replace

   The -R option used in this example sorts the profile table by the amount of real time the script spent executing a given function. The "cumm call" column reveals how many times each function was called, and the "s/call" column reveals how many seconds each call to the function required, on average.

4. To generate a calltree file that you can import into the KCacheGrind profile analysis application, issue the pprof2calltree comand.

# Contact information

If you have comments, bugfixes, enhancements or want to help developing this beast, you can send an mail to apd@mail.communityconnect.com. Any help is very welcome.

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