Talk about the kotlin cooperation process and the difference between job and supervisorjob

1. Preface

With the popularity of collaborative processes , Collaborative process knowledge is increasingly favored by interviewers . First , The interview questions of Xie Cheng are usually very concise , One or two simple words can describe the problem clearly , Second, for the interviewer , The exquisite data structure and algorithm in the collaborative process framework can well examine the applicant's mastery of basic knowledge . Compared to the of rotten Street Android stereotyped writing , It can also examine the candidate's active learning ability . The so-called expert knows whether there is . Collaborative process knowledge is the expert and touchstone in the interview scene . Gossip and less narration , This article takes you to talk about Job and SupervisorJob The difference between .

2. Job and SupervisorJob The difference between

If you have seen the official documents or videos of the cooperation process . You should know Job and SupervisorJob One difference is ,Job If an exception occurs in the sub process of, it will be cancelled at the same time Job Other subprocesses , and SupervisorJob Can't .

Job Launched the 3 The subprocess job1、job2、job3.job1 delay 100 An exception occurred after milliseconds , The collaboration was cancelled ,job2 and job3 It was also cancelled .

SupervisorJob Launched the 3 The subprocess job1、job2、job3.job1 delay 100 An exception occurred after milliseconds , The collaboration was cancelled ,job2 and job3 Not affected .

3. principle

Friends who have had interview experience should know , Interviewers like to ask principles . Why? Job and SupervisorJob There is such a difference ？

Find the answer in the source code .Job() The return is JobImpl object ,SupervisorJob() Back to SupervisorJobImpl object . and SupervisorJobImpl yes JobImpl Subclasses of , And rewritten childCancelled Method , The return value is false.JobImpl Inherited from JobSupport, its childCancelled The source code of the method is as follows ：

Job How to establish a parent-child relationship One article , Have explained childCancelled Method . Start the process Job And the process itself Job Form a father son relationship . When the collaboration is cancelled , Will call the parent Job Of childCancelled Method .SupervisorJobImpl Go straight back to false, Represent parent Job Not because Job Be cancelled and follow the cancellation . and JobSupport Would call cancelImpl Method , This method cancels the parent Job Father Job All son Job.

4. The difference between exception handling

congratulations , You are lucky to pass the previous questions , Just when you are secretly happy . The interviewer may ask , Excuse me, except for Job The cancellation of is different , Is there any other difference ？ Of course there is , For example, the exception handling mechanism is different ,Job If an exception occurs in the process started by the method , The exception will follow Job The tree has been passing up , and SupervisorJob An exception occurred in the co process started by the method ,SupervisorJob The exception will be handled by the coroutine . That's a little abstract , Look at an example .

Demonstrate collaboration nesting , There is Job When the type starts the collaboration , If the subprocess is abnormal , Exceptions will be handled by the root coroutine .

Demonstrate collaboration nesting , There is SupervisorJob When the type starts the collaboration , If the subprocess is abnormal , The exception will be handled by the subprocess .

The answer is , I thought to myself , There's nothing wrong with it now , But the interviewer then asked , What is the principle ？ Of course, the answer should be found in the source code .

Code 1 It's about , Is the core logic for handling exceptions , It first judges cancelParent The return value of , If you return false, Just call handleJobException.

cancelParent The meaning of the method is , When an exception occurs at the subprocess , Then it will try to cancel its parent process , If you return true Indicates that the parent process is also cancelled , Conversely, it means that the parent process cannot be cancelled , and cancelParent Eventually, it is also possible to call the code 2 Situated parent.childCancelled Method .

The exception handling logic can be explained by workplace examples . Suppose the unspoken rule of the workplace is , Any employee made a mistake , The first thing is to report to the superior , If your superiors are willing to deal with your mistakes , Then the employees don't have to care , If the supervisor calls back the problem to the employee , Then the mistakes have to be handled by the employees themselves

So back to the question itself ,Job It's equivalent to a good boss , The mistake made by zixie Cheng , It is willing to deal with ,SupervisorJob It's like a tough boss , Zixie Cheng's own mistake , Solve it yourself .

The processing mechanism of the coroutine exception is very complex , It is beyond the scope of this article , I will be on my knowledge planet , Explain in another article .

5. Is that enough ？

Writing at this point ,Job and SupervisorJob Make it clear. . But there are many other problems , such as ：

1. CancellationException And other Exception The difference between
2. coroutineScope And SupervisorScope The difference between

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