Process synchronization
means that when a function call is issued, the call will not return until the result is obtained. That is to say, you must do one thing one at a time, and wait until the previous one is completed before you can do the next thing.
For example: after getting up in the morning, wash up first and then eat. You cannot start eating before washing up.
According to this definition, in fact, most functions are called synchronously (such as sin, isdigit, etc.). But generally speaking, when we talk about synchronous and asynchronous, we specifically refer to tasks that require the cooperation of other components or take a certain amount of time to complete.
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The most common example is: sendmessage. This function sends a message to a window and does not return until the other party has processed the message. After the other party has finished processing, the function returns the result value returned by the message processing function to the caller.
Synchronous transmission
Usually, synchronous transmission uses data blocks as the transmission unit. A special character or bit sequence must be appended to the head and tail of each data block to mark the beginning and end of a data block. Generally, a check sequence (such as 16 bits or 32 bits) must be appended. bit CRC check code) in order to perform error control on the data block.
The so-called synchronous transmission means: the time interval between data blocks is fixed, and their time relationship must be strictly specified.
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