Introduction to opcode cache usage in PHP

This article mainly introduces the simple usage of opcode cache in PHP, and analyzes the concept, principle, simple opening and usage of opcode in the form of examples. Friends who need it can refer to it. I hope it can help everyone.

The example in this article describes the simple usage of opcode cache in PHP. Share it with everyone for your reference, the details are as follows:

1. What is opcode

After the interpreter analyzes the code, it generates an intermediate code that can be run directly, which is called an opcode, opcode

2. The difference between an interpreter and a compiler

The interpreter generates the intermediate code and directly runs the intermediate code. The control of the runtime is still in the hands of the interpreter.

The compiler generates the intermediate code and further optimizes the code to generate a target program that can be run directly, but does not execute it. It waits for the user to trigger execution. Its control is in the target program and has nothing to do with the compiler.

3.php is an interpreted language. Its principle is somewhat similar to compilation, including lexical analysis, syntax analysis, semantic analysis..., the core engine of the php interpreter is zend engine

4.php How to view the opcode of a piece of code

Install the parsekit extension of php, and you can view the opcode of php through the extended api, such as parsekit_compile_string()

php -r "var_dump(parsekit_compile_string('print 1+1;'));"

5.opcode is generated

It must first undergo lexical analysis. The script code can be regarded as a series of word combinations. The interpreter must analyze these words Classify and mark

For example, print, we look at zend/zend_language_scanner.l in the php source code package. In this file, we can find the mark corresponding to print. T_PRINT

After finding the mark, the next step is syntax analysis. In zend/zend_language_parser.y, we can find the function corresponding to T_PRINT

and then in zend/zend_compile.c Find the implementation code of this function in . This function implements the conversion of opcode. All opcodes are represented by user integers.

6. Turn on opcode caching

Generating opcode requires system overhead. Each time an opcode is executed, an opcode must be generated. This overhead is considerable, so the optimization of PHP must enable the opcode cache. , to avoid repeated compilation.

php's opcode cache includes APC, eAccelerator, and XCache, which all put opcode in shared memory.

Take APC as an example: Set

apc.cache_by_default = on

in php.ini via

<?php print_r(apc_cache_info());?>

You can check the cache status,

7.opcode cache expiration

The opcode cache will expire. If it expires, it must be generated again. Of course, you can also skip the expiration check mechanism. Set

apc.stat=off

in php.ini so that the modification of the program code takes effect by restarting the server.

8. For script tracking and analysis, you can use xdebug to track. You can use xdebug to implement a performance tracker and find the execution bottleneck of the program, thereby optimizing the program.

xdebug.profiler_output_dir = /tmp/xdebug
xdebug.profiler_output_name = cachegrind.out.%p

xdebug function tracing:

xdebug.trace_output_dir = /tmp/xdebug
xdebug.trace_output_name = trace.%c

You can use wincachegrind to view the xdebug report file under window.

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Understanding the opcodes of PHP principles_PHP tutorial

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