How to use coroutines in PHP?

With the performance bottleneck of the traditional multi-threading model in high concurrency scenarios, coroutines have become a hot topic in the field of PHP programming. A coroutine is a lightweight thread that can implement concurrent execution of multiple tasks in a single thread. In the PHP language ecosystem, coroutines have been widely used. For example, frameworks such as Swoole and Workerman provide support for coroutines.

So, how to use coroutines in PHP? This article will introduce some basic usage methods and common precautions to help readers understand the operating principles of coroutines and how to reasonably use coroutines to improve code performance in actual development.

The basic concept of coroutines

In the traditional multi-threading model, each thread has its own execution stack, registers and other resources. When threads switch, the state of the current thread needs to be saved and the state of the other thread restored. This state transition is very expensive and is not conducive to performance optimization in high concurrency scenarios. Coroutines are a more lightweight method of concurrent processing. They do not require additional threads or processes to support them. Instead, they use the time slice of a single thread to execute multiple tasks alternately to achieve the effect of concurrent processing. .

Coroutines are concurrent programming models based on the idea of ​​"collaborative multitasking". Its core is "suspend" and "resume" operations. In a coroutine, each task is a coroutine. Its execution will not be forcibly interrupted. Instead, it will actively suspend when encountering a blocking operation and wait for other coroutines to complete execution before resuming execution, thereby achieving a single task. The effect of concurrent processing of multiple tasks within a thread.

How to use coroutines

In the PHP language, the implementation of coroutines depends on specific frameworks and extension libraries, such as Swoole, Workerman, ReactPHP, etc. These frameworks provide the infrastructure for coroutine programming. Developers only need to follow specific APIs and development specifications to transform asynchronous non-blocking programs into coroutine-style synchronous blocking programs.

Taking Swoole as an example, the following is a simple coroutine example:

Create a new coroutine through the SwooleCoroutineun() method and execute the specified callback function . Inside the callback function, we can use the methods of the SwooleCoroutine class to implement various operations of the coroutine, such as Coroutine::sleep() simulate blocking waiting, Coroutine::yield ()Give up execution rights, etc. After the coroutine is executed, call the SwooleCoroutine::close() method to release the resources. 
In coroutine programming, our most common application scenario is asynchronous non-blocking I/O operations, such as file reading and writing, network requests, etc. In order to simplify asynchronous programming, a common approach is to use coroutines to encapsulate asynchronous operations and program them as synchronous blocking, thus simplifying the logical structure of the code. 
The following is a file read and write operation encapsulated using Swoole coroutine: 
In the above code, we use the fopen() method to open a file, and then Use the SwooleCoroutineSystem::read() method to read file data. In the coroutine, since file reading and writing are blocking IO operations, we do not need to use a callback function, but directly write the code in a synchronous blocking manner. Through the coroutine scheduling mechanism, we can ensure that other coroutines can continue to execute during the file reading and writing process. 
Notes on coroutines
Although coroutines can effectively improve the concurrent processing efficiency of programs, you need to pay attention to some details when using coroutines to avoid various strange problems. mistake. 
Coroutine scheduling is expensive
Although coroutine switching is much faster than thread or process switching, when there are a large number of coroutines, the coroutine The overhead of program scheduling is still not negligible. Therefore, when using coroutine programming, you should try to control the number of coroutines and avoid frequent switching operations. 
Coroutines cannot cross-process
Coroutines are based on a single-process model design and cannot support cross-process sharing of resources. Therefore, thread safety should be paid attention to when using coroutines. and process isolation issues. 
Coroutines may cause resource leaks
Because the way coroutines work is different from threads or processes, resource leaks can easily occur in coroutine programming. question. For example, forgetting to release resources, asynchronous calls within loops, etc. Therefore, you need to pay special attention to resource management and memory usage when programming with coroutines. 
Conclusion
This article introduces the basic concepts, usage and precautions of PHP coroutines. By understanding the working principles and practical application scenarios of coroutines, we can better master coroutine programming technology and handle large-scale concurrent tasks in a more efficient manner. In actual project development, coroutines have become an essential skill. I believe that the scope of use of coroutines will become more and more extensive in the future. 
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