php - Capturing (externally) the memory consumption of a given Callback

Question

The Problem

Lets say I have this function:

function hog($i = 1) // uses $i * 0.5 MiB, returns $i * 0.25 MiB
{
    $s = str_repeat('a', $i * 1024 * 512); return substr($s, $i * 1024 * 256);
}

I would like to call it and be able to inspect the maximum amount of memory it uses.

In other words: memory_get_function_peak_usage($callback);. Is this possible?

---

What I Have Tried

I'm using the following values as my non-monotonically increasing $i argument for hog():

$iterations = array_merge(range(0, 50, 10), range(50, 0, 5));
$iterations = array_fill_keys($iterations, 0);

Which is essentially:

(
    [0] => 0
    [10] => 0
    [20] => 0
    [30] => 0
    [40] => 0
    [50] => 0
    [45] => 0
    [35] => 0
    [25] => 0
    [15] => 0
    [5] => 0
)

---

Enclosing with memory_get_usage()

foreach ($iterations as $key => $value)
{
    $alpha = memory_get_usage(); hog($key);
    $iterations[$key] = memory_get_usage() - $alpha;
}

print_r($iterations);

Output:

(
    [0] => 96
    [10] => 0
    [20] => 0
    [30] => 0
    [40] => 0
    [50] => 0
    [45] => 0
    [35] => 0
    [25] => 0
    [15] => 0
    [5] => 0
)

If I store the return value of hog(), the results start to look more realistic:

foreach ($iterations as $key => $value)
{
    $alpha = memory_get_usage(); $s = hog($key);
    $iterations[$key] = memory_get_usage() - $alpha; unset($s);
}

print_r($iterations);

Output:

(
    [0] => 176
    [10] => 2621536
    [20] => 5242976
    [30] => 7864416
    [40] => 10485856
    [50] => 13107296
    [45] => 11796576
    [35] => 9175136
    [25] => 6553696
    [15] => 3932256
    [5] => 1310816
)

As expected, now it's showing me the amount of memory returned, but I need the total memory used.

---

Using register_tick_function():

I didn't knew, but it turns out that when you do:

declare (ticks=1)
{
    $a = hog(1);
}

It won't tick for every line, statement or block of code inside of hog() function, only for the code inside the declare block - so, unless the function is defined within it, this option is a no go.

---

Mixing with gc_* functions:

I tried (without much hope I must say) using combinations of gc_disable(), gc_enable() and gc_collect_cycles() with both experiments above to see if anything changed - it didn't.

Answer 1

I was digging in the PHP manual and I found the memtrack extension, not perfect but it's something.

---

EDIT: I had heard about it, but never actually tried it before. Turns out XHProf is all I needed:

$flags = array
(
    XHPROF_FLAGS_CPU,
    XHPROF_FLAGS_MEMORY,
    XHPROF_FLAGS_NO_BUILTINS,
);

$options = array
(
    'ignored_functions' => array
    (
        'call_user_func',
        'call_user_func_array',
        'xhprof_disable',
    ),
);

function hog($i = 1) // uses $i * 0.5 MiB, returns $i * 0.25 MiB
{
    $s = str_repeat('a', $i * 1024 * 512); return substr($s, $i * 1024 * 256);
}

---

Test #1:

xhprof_enable(array_sum($flags), $options);

hog(4);

$profile = xhprof_disable();

print_r($profile);

Output:

    [main()==>hog] => Array
        (
            [ct] => 1
            [wt] => 54784
            [mu] => 384
            [pmu] => 3142356
        )

    [main()] => Array
        (
            [ct] => 1
            [wt] => 55075
            [mu] => 832
            [pmu] => 3142356
        )

mu is memory usage, pmu is peak memory usage, 3142356 / 1024 / 1024 / 0.5 = 4 = $i.

---

Test #2 (without XHPROF_FLAGS_NO_BUILTINS):

    [hog==>str_repeat] => Array
        (
            [ct] => 1
            [wt] => 21890
            [cpu] => 4000
            [mu] => 2097612
            [pmu] => 2094200
        )

    [hog==>substr] => Array
        (
            [ct] => 1
            [wt] => 17202
            [cpu] => 4000
            [mu] => 1048992
            [pmu] => 1048932
        )

    [main()==>hog] => Array
        (
            [ct] => 1
            [wt] => 45978
            [cpu] => 8000
            [mu] => 1588
            [pmu] => 3143448
        )

    [main()] => Array
        (
            [ct] => 1
            [wt] => 46284
            [cpu] => 8000
            [mu] => 2132
            [pmu] => 3143448
        )

Whoohoo! Thanks Facebook!

---

From the XHProf docs:

It is worth clarifying that that XHProf doesn't strictly track each allocation/free operation. Rather it uses a more simplistic scheme. It tracks the increase/decrease in the amount of memory allocated to PHP between each function's entry and exit. It also tracks increase/decrease in the amount of peak memory allocated to PHP for each function.