Deeply understand the concepts of synchronization and asynchrony, blocking and non blocking, parallel and serial

One 、 background

In the evening, a friend in the technology group asked ,“ What is the difference between synchronization and blocking color ?”

Many friends gave their opinions , Some of the contents are as follows ：

Among them, a friend gave a screenshot , The figure shows the comparison “ vivid ” Example .

However , After reading it, I seem to understand , I don't seem to understand .

Many people think about these common concepts , It seems familiar and strange .

Two 、 understand

2.1 Leading edge

If a classmate had seen mine before 《 In my eyes Java Daniel's lonely teacher 》 This article , You will find that one or two have been mentioned in it , Unfortunately, most students only want to ask and see when they encounter problems .

2.2 visual angle

For this question , I prefer to see it from a perspective .

Synchronous and asynchronous are the perspectives of function calls

That is, after synchronously executing function calls , You must wait for the function to return to continue ; Asynchrony does not need to wait for return to continue to perform other tasks .

For example, the leader arranges you to print an e-book with hundreds of pages , Synchronization is equivalent to printing yourself , While printing, I have been waiting at the side of the printing machine for printing to complete , Do other things ; Asynchronously, we click Print and then do other things , For example, click Print to brush a play first, or we ask another classmate to print it for us , Then do other things by yourself .

Go back to specific business , Suppose we need to send a text message to the user after the system login is successful , After we log in , Use the thread pool to start the thread or send a message queue message to notify the downstream to send SMS , The login method can return directly without waiting for the execution of the SMS program .

Blocking and non blocking are thread perspectives

in my opinion , Blocking and non blocking describe thread state .
Blocking means that the current thread is suspended after a call is executed （ As in the production consumer model , When there is no consumer content wait）, Release CPU , Until the result is awakened （ When there is consumable content adopt notifyAll Wake up consumer thread ）; Non blocking is when a call is executed , Even if you can't get the results immediately , The current thread will not be suspended .

Like taxi drivers , After receiving the passengers , The front sign will turn to [ someone ], We can't continue to receive guests at this time , Know that the passengers get off and end the order , This is it. [ Blocking ]; The taxi driver does not turn the sign to [ someone ], Even if a passenger is not delivered to the destination , You can continue to take orders , That was [ Non blocking ].

Usually [ Blocking ] It will cause the thread to enter the suspended state （ The effect is like calling wait Method ）,[ Sync ] When called, the thread is still running , Executing function call （ The effect is like calling sleep Method ）, It's just that the call hasn't returned .

Parallel and serial are CPU visual angle

Parallel tasks can usually be split into multiple steps , Multiple CPU Execute together with the core , There is usually no dependency between such tasks , Completely orthogonal ; Each step of a serial task can only be executed by one core at the same time , There are usually upstream and downstream dependencies .

We can compare multiple people to multiple people CPU The core . For example, we want to put elephants in the refrigerator , You have to open Refrigerator door , Then put the elephant in , Then close the refrigerator door , Even if we have more than one person , But the steps cannot be performed at the same time . That is, you can't directly install elephants before the refrigerator door is opened , You can't just close the refrigerator door before the elephant goes in , This is it. [ Serial ].

If we want to publish a Book , The book can be divided into different chapters , Then each person is divided into a chapter , Let's write together , At this time, many people are doing tasks together , And it's helpful to the progress , This is it. [ parallel ].

Follow this example , We want to [ parallel ] and [ Concurrent ] The difference between , There's quite a lot of concurrency. There's only one of us , You can write the first chapter later , Write the second chapter later , Write chapter three later , Then write the first chapter , Although you can switch to do different things , But only one person .

3、 ... and 、 summary

For these concepts , I hope you can grasp the essence , Don't be confused by various examples .
Synchronous and asynchronous are the perspectives of function calls , The judgment is based on whether it is necessary to Waiting to return .
Blocking and non blocking are thread perspectives , That is, whether the current thread is called Hang up .
Parallel and serial are CPU visual angle , I.e. Yes No meanwhile There are multiple cores undertaking the same task together .

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This article just talks about my understanding , If there are omissions , You can comment and communicate with me , You are also welcome to give a more understandable way of understanding .

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It's not easy to create , If this article helps you , Welcome to thumb up 、 Collection and attention , Your support and encouragement , It's the biggest driving force of my creation .