The latest five PHP+Swoole/Go interview questions (with answers)

1. The principle of Swoole coroutine

Swoole and Go both support coroutines, and their coroutine implementation principles are different:

Swoole principle:

Swoole is a PHP coroutine framework implemented based on C. It implements coroutine scheduling and event driving through underlying epoll, reactor, worker and other technologies. In Swoole, extraordinary concurrency processing can be achieved through coroutines.

In Swoole, coroutines are implemented through the extended PHP kernel, which relies on epoll, reactor, worker and other technologies to schedule PHP coroutines. For a coroutine task, Swoole uses a state machine design method to encapsulate each state of the task into a function, thereby achieving full control of the coroutine.

Go principle:

The Go language has built-in support for coroutines, and the scheduling of coroutines is achieved by using Go's scheduler. In Go language implementation, a scheduler based on M:N is used, where M represents system threads and N represents user-level threads (coroutines). The scheduler will bind multiple coroutines to a small number of threads.

In Go, the implementation of coroutine is called goroutine. Goroutine dynamically increases and decreases system threads as needed, which makes Goroutine scheduling more flexible and efficient. When a Goroutine blocks, the scheduler will suspend it and then continue to schedule other Goroutines, thereby improving the execution efficiency of the Goroutine. At the same time, Go's scheduler will bind multiple Goroutines to one M, and bind multiple M to multiple system threads, which can effectively improve performance.

In general, the coroutine implementation principles of Swoole and Go are based on the principle of event loop, and the underlying implementation methods are slightly different.

2. The swoole coroutine needs to pay attention to the following points:

1. The coroutine cannot perform blocking operations: The original design of the coroutine is to avoid thread or process blocking, so it cannot be used in the coroutine. Blocking operations, such as network operations, should be performed in an asynchronous, non-blocking manner.
2. Avoid multiple switching: The overhead of coroutine switching is very small, but multiple switching will accumulate overhead and affect performance. Therefore, coroutine switching should be minimized.
3. Pay attention to memory management: The memory space is shared between coroutines, so special attention needs to be paid to memory management to avoid problems such as memory leaks.
4. It is forbidden to close the socket within the coroutine: Because the socket is shared between coroutines, if the socket is closed within the coroutine, other coroutines will be unable to continue to use the socket, resulting in an exception in the program.
5. Global variables cannot be used: memory space is shared between coroutines. If global variables are used, conflicts may occur when global variables are accessed at the same time.
6. Beware of infinite loops: You need to use co::exit or return statements to exit the coroutine to avoid abnormal situations such as infinite loops.
7. Depends on Swoole extension: When using the Swoole coroutine, you need to ensure that the Swoole extension has been installed and loaded normally, otherwise it will cause errors or become unusable.

3. The difference between Swoole and Workerman

1. Swoole is an asynchronous programming framework, while Workerman uses multi-process programming. Due to the efficiency and stability of asynchronous programming technology, Swoole has obvious advantages in performance and load balancing.
2. In the case of asynchronous programming, Swoole's event loop mechanism has better performance and scalability, while Workerman's multi-process solution can fully utilize the performance of multi-core processors.
3. From a code design perspective, Swoole provides more APIs and functions to easily implement high-performance network applications. Workerman's API is more concise and clear, and more suitable for beginners.
4. Swoole supports coroutines and can make full use of CPU resources. Although workerman can share data between processes, it is not very good at sharing memory between processes.

4. Swoole coroutines communicate in various ways

1. Coroutine context
2. Swoole coroutine communication API: Swoole provides some coroutines APIs for process communication, such as chan, go, etc., can be used for task allocation and result return between coroutines.
3. Global variables: Data can also be exchanged between Swoole coroutines through PHP's global variables. This requires ensuring that the variables are not modified and accessed by multiple coroutines at the same time. You can use the Lock, Condition, etc. provided by Swoole. Tools to achieve synchronous access to shared variables between coroutines.
4. Topic/Channel: Similar to a message queue, Swoole's Topic/Channel can be used to send and receive messages between coroutines, distribute asynchronous tasks, broadcast event messages, etc.
5. Coroutine waiting and wake-up mechanism for I/O operations such as MySQL: When using Swoole coroutine for I/O operations such as MySQL, you can use the coroutine waiting and wake-up mechanism provided by Swoole coroutine to make the program When waiting for I/O operations, you can immediately switch to other coroutines to improve the concurrency performance of the program.

5. Common optimization methods for PHP code

1. Use memory-resident frameworks such as swoole, and use coroutines and connection pools to improve concurrency
2. Reduce Database query: Try to avoid repeatedly querying the database. You can use caching technology, such as memcached and Redis, to store query results.
3. Code caching: Using caching tools such as APC (Alternative PHP Cache), OPcache, and XCache can greatly improve the performance of PHP programs. This method caches the compiled PHP script into memory so that it can be read directly the next time it is executed.
4. Reduce HTTP requests: Merging CSS, JavaScript, image CSS Sprites, lazy loading and other methods can reduce HTTP requests, thereby improving web page performance.
5. Reduce code duplication: abstract the same part of the code so that it can be called multiple times. This can reduce code duplication and increase the speed of PHP programs.
6. Reduce the use of regular expressions: Although regular expressions are very powerful, their operating efficiency is relatively low. Use regular expressions as little as possible in PHP programs.
7. Avoid overloading: If you only need to use one function, don't load the entire class. Only necessary PHP extensions are loaded.
8. Compress the variables in the PHP code into the local environment as much as possible to avoid the use of global variables.
9. Use cached templates: Cached templates such as Smarty can reduce the pressure on the server and increase the display speed of the page.
10. Use efficient string functions: PHP provides many efficient string processing functions, such as str_replace, substr, preg_match, etc. Using these functions can increase the speed of your PHP program.

11. Use the latest version of PHP: Each new version of PHP has new performance optimizations. Using the latest version of PHP can greatly improve the running speed of PHP programs.

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