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 0 or 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 10 is converted to binary. It will be 00001010;
- Decimal -10 would be 10001010 in binary. Leftmost digit of the number indicates the sign. 1 is minus, 0 is plus;
- 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 1.
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 246.
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”.
If you still have any questions, feel free to ask me in the comments under this article, or write me on firstname.lastname@example.org.
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