PHP7 Kernel Analysis 3 Variables

The content of this article introduces CGI and FastCGI about PHP7 kernel analysis 1. Now I share it with everyone. Friends in need can refer to it

1. Variable structure

2. Variable type

Among them, undef, true, false and null have no value and are directly distinguished according to type, while long , the value of double is stored directly in value, and other types are pointers

3. String

4. Array

HashTable mainly relies on arData to realize the storage and indexing of elements. When inserting an element, first insert the element into the Bucket array in order, the position is idx, and then map it to a certain position nIndex in the hash table according to the hash value of the key, and store idx in this position; when searching, first in the hash table Map to nIndex, get the position idx of value in the Bucket array, and then take out the element from the Bucket array.

Hash collision: When a conflict occurs, save the position of the original value to zval.u2.next of the new value, and then add the new value value replaces the original value position

Expansion: The size of the PHP hash table is 2^n. If the capacity is not enough during insertion, the proportion of deleted elements will be first checked. If the threshold is reached, the deleted elements will be removed. Rebuild the index. If the threshold is not reached, perform an expansion operation to double the current size, copy the current Bucket array to the new space, and then rebuild the index.

Rebuild the hash table: When the deleted elements reach a certain number or the capacity is expanded, the hash table needs to be rebuilt because the value has moved in the Bucket position or the hash array nTableSize has changed, causing the mapping relationship between key and value to change. The reconstruction process The actual process is to traverse the values ​​in the Bucket array, then recalculate the mapping value and update it to the hash table, remove the deleted value, and move the subsequent undeleted values ​​forward in sequence

5. Reference

Reference is a special type in PHP. It actually points to another PHP variable. Modifying it will directly change the zval actually pointed to. You can simply Understood as a pointer in C, a reference variable is generated through the & operator in PHP. That is to say, no matter what the previous type is, & will first create a zend_reference structure with a zval embedded in it. The value of this zval points to the original The value of zval (if it is a Boolean, integer, or floating point, copy the original value directly), and then change the type of the original zval to IS_REFERENCE, and the value of the original zval points to the newly created zend_reference structure.

6. Reference counting

Not all data types use reference counting, long and double directly It is a hard copy, and only those types whose value is a pointer (except interned string, immutable array) can use reference counting. Can be judged by zval.u1.type_flag

7. Copy on write

In fact, only string and array are supported,

8. Garbage collection

Recycling of PHP variables There are two main types: active destruction and automatic destruction. Active destruction refers to unset, and automatic destruction is PHP's automatic management mechanism. When returning, the refcount of local variables is subtracted. Even if there is no explicit return, PHP will automatically add this operation. The other is copy-on-write. When the original value is pointed to, the refcount of the old value after the disconnection will also be checked.

Reference relationship before unset($a):

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PHP7 Kernel Analysis 1 CGI and FastCGI

PHP7 Kernel Analysis 2 I/O Model

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