Differences between synchronous requests and asynchronous requests in http requests

For a WEB programmer, if he does not know the synchronous and asynchronous execution modes, he will send an operation statement (query or read a record) to the server, it is dangerous to set the execution result returned by the referenced server or perform the next operation on the result. For a simple process, there will be no major problems, but if a complicated operation process is involved, for example, the subsequent statements on the client are executed after the operation statement is released. However, for various reasons, the server may not be able to execute the operation statement, the result is returned to the client before subsequent statement execution. When a subsequent statement references the execution result of a previous operation statement, it often references an incorrect value because the execution result does not exist, resulting in system errors or deadlocks, therefore, you should carefully select the corresponding request mode based on the actual situation.

First, let's take a look at the definitions of synchronous and asynchronous requests in http requests:

Synchronous request refers to the communication mode in which the sender sends a packet only after the receiver sends a response.

Asynchronous request refers to the communication mode in which the sender continues to send the next packet after the sender sends the data before receiving the response from the receiver.

Although asynchronous execution mode is more difficult than synchronous execution mode, asynchronous mode can implement multi-task parallel execution, greatly improving user experience and program execution efficiency. In application development, you need to determine whether the synchronous mode or asynchronous mode is selected based on the actual situation. When the query or modification to the database is relatively simple, it is enough to select the synchronous execution mode, which can return the result data in a few seconds or less. In addition, asynchronous execution mode is not necessary when the application cannot continue execution before obtaining the result set. It may take a long time to complete the UPDATE or DELETE operations between complex queries, especially between multiple complex tables. In this case, it is best to adopt the asynchronous execution mode, allows you to operate other parts of the program at the same time.

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