I was happily working on a small java project, and after just creating a new Java class, and typed around 100 lines in the Eclipse editor, the whole IDE froze. It seems there is a bug in Luna that will freeze the IDE on out of memory condition, and I have just hit it.
100 lines is not that much of a loss generally, I can write them again. But why? Aren’t computers supposed to save us from the manual work. I wanted this file back 🙂 Quick check on the file system showed that after creating the class Eclipse saved and empty class inside. I had to find another way I guess.
What if I somehow manage to connect a Java debugger and search for the file in memory. Unfortunately I am not that proficient in Java and doing all the research on how to do it may take quite some time. So lets see do I really need a debugger ? I just need the file, and it is somewhere in the Eclipse process memory. Getting the whole memory of a process is quite easy in Linux :
gcore `pgrep java`
And voila, we have the whole memory of the process saved to core.<PID> . Now lets find that file. strings comes to mind instantly :
strings core.5607 | gview -
And I started searching for occurrence of ‘class MetadataInfo’ ( that was my class name) . Unfortunately while MetadataInfo had plenty of instances none of them was preceded by a class keyword and none was actually in the content of my file. Hmm, maybe the file isn’t stored as plain string, maybe it is some kind of tree for easier syntax t highlighting, as there were pieces of the file all over the place. But then it occurred to me that the file is probably stored in UTF16 in memory as Java is very much into UTF16. Quick check shows that strings supports several encodings :
$ strings --help
......
-e --encoding={s,S,b,l,B,L} Select character size and endianness:
s = 7-bit, S = 8-bit, {b,l} = 16-bit, {B,L} = 32-bit
.......
Nice! Lets try 16-bit LE as I am on an Intel machine:
strings -e l core.5607 | gview -
Now searching for ‘class MetadataInfo’ finds several occurrences of the full file, I guess because of the Local History that Eclipse keeps for each file. Just copied one that seems good enough, saved it to file and killed the frozen Eclipse w/o significant data loss.