Dump all variables in PHP

问题:

There's a memory leak in my script and I couldn't find it after 2 days. I found the loop that is causing the memory leak; each iteration of the loop increases the memory usage. I moved the loop into a function to isolate the variables. At the end of the function, I unsetted every variable created by the function so that get_defined_vars() returns an empty array. Here's what I mean:

function the_loop(){
  $var="value";

  ... // processing, including using a library

  unset($var);
  print_r(get_defined_vars()); // prints empty array
}

while(true){
  the_loop();
  echo memory_get_usage()."\n"; // steadily increases until memory limit is reached
}

I'm guessing that some variables defined in the_loop() are still in memory. I tried using XDebug's trace tool, but it didn't help. All it showed was that memory usage increases on average over the long run. I'm looking for a tool that can show me all the values in PHP's memory. I will be able to recognize the variable based on the value. What tool can dump PHP's memory?

回答1:

As Dragon mentioned unset doesn't instantly free memory.

What's better at freeing memory with PHP: unset() or $var = null

I'd consider re-evaluating the way you're using PHP, it's not designed for long/constant running scripts, the garbage handler simply isn't that great.

If you want to dig further into the executing script I'd suggest checking out some tools like:

https://github.com/jokkedk/webgrind

http://xhprof.io/

http://derickrethans.nl/xdebug-and-tracing-memory-usage.html

Also worth a read: What gc_collect_cycles function is useful for?

回答2:

Calling unset() does not force garbage collection, so while the reference count should decrease there may be others referencing it. Use xdebug_debug_zval($var) before calling unset to see how many references to its value there actually are.