PHP shared memory function usage and application

PHP Shared Memory Function Usage and Application

Shared memory refers to the technology in which multiple processes access the same memory space at the same time. In concurrent programming, shared memory can be used for inter-process communication to achieve data sharing between different processes. PHP also provides related shared memory functions. This article will introduce the usage of PHP shared memory functions and explore some practical application scenarios.

1. Use of shared memory functions

PHP provides the shmop extension module, which allows PHP to operate on system shared memory. The functions provided by this extension module include:

1.1. shmop_open

The shmop_open function is used to open a system shared memory object and return the identifier of the shared memory object. The parameters of this function are as follows:

shmop_open(int $key, string $flags, int $mode, int $size)

Parameter description:

• $key: Identifier of the shared memory object (required parameter).
• $flags: used to specify the read and write permissions of shared memory (required parameters). This parameter can be "r", "w" or "rw", which stands for read-only, write-only and read-write respectively. If "r" is used, the shared memory contents can only be read and cannot be modified. If "w" is used, content can only be written to the shared memory, but cannot be read. If "rw" is used, shared memory can be read and written.
• $mode: Create access permissions for shared memory (required parameter). This parameter can be an octal quantity. For example: "0644".
• $size: The memory size to be shared (required parameter).

Example:

$key = ftok(__FILE__, 'a'); //获取共享内存的key
$shm = shmop_open($key, "c", 0644, 100); //打开共享内存，大小为100字节

1.2. shmop_read

The shmop_read function is used to read data from shared memory. The parameters of this function are as follows:

shmop_read(int $shm_identifier, int $start, int $count)

Parameter description:

• $shm_identifier: Identifier of the shared memory object (required parameter).
• $start: The starting position of reading data (required parameter).
• $count: The length of data to be read (required parameter).

Example:

$content = shmop_read($shm, 0, 100); //读取共享内存的内容

1.3. shmop_write

The shmop_write function is used to write data to shared memory. The parameters of this function are as follows:

shmop_write(int $shm_identifier, string $data, int $offset)

Parameter description:

• $shm_identifier: Identifier of the shared memory object (required parameter).
• $data: String data to be written (required parameter).
• $offset: starting position of written data (optional parameter). If not specified, writing starts from the beginning of the shared memory.

Example:

$content = "This is a test."; //定义写入数据
$len = strlen($content);  //计算数据长度
shmop_write($shm, $content, 0);  //写入共享内存

1.4. shmop_size

The shmop_size function is used to obtain the size of shared memory. The parameters of this function are as follows:

shmop_size(int $shm_identifier)

Parameter description:

• $shm_identifier: Identifier of the shared memory object (required parameter).

Example:

$size = shmop_size($shm); //获取共享内存的大小

1.5. shmop_delete

The shmop_delete function is used to delete shared memory objects. The parameters of this function are as follows:

shmop_delete(int $shm_identifier)

Parameter description:

• $shm_identifier: Identifier of the shared memory object (required parameter).

Example:

shmop_delete($shm); //删除共享内存对象

2. Practical application of shared memory

The most common application of shared memory is data sharing between multiple processes. For example, in concurrent programming, if multiple processes share the same data, shared memory can be used to synchronize the data. Below we will introduce two practical application scenarios.

2.1. TCP server

In a typical multi-process TCP server architecture, each client connection is handled by a child process. In order to prevent multiple processes from accessing the server's global variables at the same time, we can use shared memory to store the values ​​of global variables. When the client connects, each child process will read the latest value of the global variable from the shared memory, thereby ensuring that all processes can access the latest global variable value.

2.2. Large-scale data calculation

In large-scale data calculation, we usually need to divide the data into multiple tasks and process these tasks in parallel by multiple processes. In order to avoid data competition between processes, we can store all data in shared memory, and each process reads the data at the same time and calculates the results at the same time. This can make data access between processes more efficient and reduce the overhead caused by data copying.

Summary

This article introduces the usage of PHP shared memory functions and discusses some practical application scenarios. Although shared memory can bring many benefits, you also need to pay attention to the access permission control of shared memory to avoid data leaks and security risks. When using shared memory, you need to carefully consider security issues and carefully design the memory structure and data format of the shared memory.

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