Programming PHP

If you compile the Apache module version of PHP with the --enable-memory-limit
switch, it will add the script’s peak memory usage to the Apache r->notes table. You
can access this information from other Apache modules, such as mod_log_config.
Add this string to your Apache LogFormat line to log the peak number of bytes a
script used:
%{mod_php_memory_usage}n
If you’re having problems with a module allocating too much memory and grinding
your system into the ground, build PHP with the memory-limit option enabled. This
makes PHP heed the memory_limit directive in your php.ini file, terminating a script if
it tries to allocate more memory than the specified limit. This results in errors like
this:
Fatal error: Allowed memory size of 102400 bytes exhausted at ...
(tried to allocate 46080 bytes) in /path/script.php on line 35
The pval/zval Data Type
Throughout the PHP source code, you will see references to both pval and zval.
They are the same thing and can be used interchangeably. The pval/zval is the basic
data container in PHP. All data that is passed between the extension API and the
user-level script is passed in this container. You can dig into the header files further
yourself, but in simple terms, this container is a union that can hold either a long, a
double, a string including the string length, an array, or an object. The union looks
like this:
typedef union _zvalue_value {
long lval;
double dval;
struct {
char *val;
int len;
} str;
HashTable *ht;
zend_object obj;
} zvalue_value;
The main things to learn from this union are that all integers are stored as longs, all
floating-point values are stored in double-precision, and every string has an associated
string length value, which, if properly checked everywhere, makes strings in
PHP binary-safe. * Strings do not need to be null-terminated, but since most thirdparty
libraries expect null-terminated strings it is a good idea to always null-terminate
any string you create.
* Binary-safe, sometimes referred to as 8-bit clean, means that a string can contain any of the 256 ASCII values,
including the ASCII value 0.
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