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| -rw-r--r-- | HACKING | 29 |
1 files changed, 29 insertions, 0 deletions
@@ -0,0 +1,29 @@ +When creating servers that can lock up the computer in some matter, it is +important to set `server_characteristics.fork_for_safety = 1` and set clean +up code in `fork_cleanup`. This should also be done if there is a risk for +global memory leaks such as IPC semaphores that have not be removed. Everything +that must be cleaned up should be initialised before `server_initialised` is +called and cleanup properly if the server failes before `server_initialised` +has be successfulled invoked. After `server_initialised` has returned with a +zero value the cleanups should be done in `fork_cleanup`. Keep in mind that +`fork_cleanup` is only called if `server_characteristics.fork_for_safety == 1`. + +Additionally it is good practice to have another computer which you can use to +SSH into the development computer and kill a server that is looking up the +computer. If a server has a child process that is the same program, the child +is probably the fork created by `server_initialised` when +`server_characteristics.fork_for_safety == 1`. If these cases, it is the child +process that should be killed and the parent process should be left alone. If +you do not have another computer you can use, you should use the `--alarm=` +option on the server to make it kill itself after a select time period. On +`server_initialised` the parent processes alarm will be transfered to the +child process. There is a race codition here, the alarm could be triggered +after the fork but before the child server has acknowledged this marked to +not do the cleanup, additional there is not specification on whether how +the return value of `alarm` is rounded, if an OS would return 0 if the +time left is for example 0,25 seconds, the alarm would be disabled. Therefore +do not make the value of the `--alarm=` option to small like for example +one second (that is `--alarm=1`). Note that the alarm is restricted by +`src/mds-base.c` to be at most one minute, any value larger than 60 will +be truncated down to 60. + |