Truncating the current log file while a reader is still reading through
it results in log lines getting missed. In contrast, rotating the file
allows readers who have the file open can continue to read from it
undisturbed. Rotating frees up the file name for the logger to create a
new file in its place. This remains true even when max-file=1; the
current log file is "rotated" from its name without giving it a new one.
On POSIXy filesystem APIs, rotating the last file is straightforward:
unlink()ing a file name immediately deletes the name from the filesystem
and makes it available for reuse, even if processes have the file open
at the time. Windows on the other hand only makes the name available
for reuse once the file itself is deleted, which only happens when no
processes have it open. To reuse the file name while the file is still
in use, the file needs to be renamed. So that's what we have to do:
rotate the file to a temporary name before marking it for deletion.
Signed-off-by: Cory Snider <csnider@mirantis.com>
This makes sure, on Windows, that all files are opened with
FILE_SHARE_DELETE.
On non-Windows this just calls the same `os.Open()`.
Signed-off-by: Brian Goff <cpuguy83@gmail.com>
This fixes issues where one goroutine tries to delete or rename a file
while another goroutine has the file open (e.g. a log reader).
Signed-off-by: Brian Goff <cpuguy83@gmail.com>
