In the previous article, we already figured out how to terminate a container with a specific exit code.
To begin with, the return value must be smaller then
256. You can notice that:
- If you terminate the container with a code of
0or some other positive number, then the same code will be sent to AppMaster.
- If you terminate the container with a negative code, then another number will be sent to AppMaster.
This is because the Spring Boot Yarn works with exit code at a low level, and two’s complement representation is used for negative exit codes. Let’s take exit code =
-10 for example.
Exit code value usually takes 1 byte. Now the following algorithm happens:
- The decimal number
10is converted to binary. It will be
10001010in binary. Leftmost digit of the number indicates the sign.
- This code in ones’ complement representation will be like this:
11110101. Here we have inverted all the digits except for the signed one (leftmost);
- This code in two’s complement representation will be like this:
11110110. We just added
In total, exit code =
-10, presented in two’s complement will be
11110110. It looks strange that Spring Boot Yarn on the AppMaster side does not convert back from two’s complement to normal representation. It simply converts the code to the decimal system.
11110110 in binary will be
246 in decimal.
It turns out that if the container terminated with code
-10, the AppMaster will receive information that the container terminated with code
For simplicity, we can think of it like this: if we terminated the container with code
minus N, AppMaster will receive code
256 minus N.
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