Fix journald and logfile-powered (jsonfile, local) log readers
incorrectly filtering out messages with timestamps < Since which were
preceded by a message with a timestamp >= Since.
Signed-off-by: Cory Snider <csnider@mirantis.com>
File watches have been a source of complexity and unreliability in the
LogFile follow implementation, especially when combined with file
rotation. File change events can be unreliably delivered, especially on
Windows, and the polling fallback adds latency. Following across
rotations has never worked reliably on Windows. Without synchronization
between the log writer and readers, race conditions abound: readers can
read from the file while a log entry is only partially written, leading
to decode errors and necessitating retries.
In addition to the complexities stemming from file watches, the LogFile
follow implementation had complexity from needing to handle file
truncations, and (due to a now-fixed bug in the polling file watcher
implementation) evictions to unlock the log file so it could be rotated.
Log files are now always rotated, never truncated, so these situations
no longer need to be handled by the follow code.
Rewrite the LogFile follow implementation in terms of waiting until
LogFile notifies it that a new message has been written to the log file.
The LogFile informs the follower of the file offset of the last complete
write so that the follower knows not to read past that, preventing it
from attempting to decode partial messages and making retries
unnecessary. Synchronization between LogFile and its followers is used
at critical points to prevent missed notifications of writes and races
between file rotations and the follower opening files for read.
Signed-off-by: Cory Snider <csnider@mirantis.com>
The LogFile follower would stop immediately upon the producer closing.
The close signal would race the file watcher; if a message were to be
logged and the logger immediately closed, the follower could miss that
last message if the close signal (formerly ProducerGone) was to win the
race. Add logic to perform one more round of reading when the producer
is closed to catch up on any final logs.
Signed-off-by: Cory Snider <csnider@mirantis.com>
Whether or not the logger has been closed is a property of the logger,
and only of concern to its log reading implementation, not log watchers.
The loggers and their reader implementations can communicate as they see
fit. A single channel per logger which is closed when the logger is
closed is plenty sufficient to broadcast the state to log readers, with
no extra bookeeping or synchronization required.
Signed-off-by: Cory Snider <csnider@mirantis.com>
followLogs() is getting really long (170+ lines) and complex.
The function has multiple inner functions that mutate its variables.
To refactor the function, this change introduces follow{} struct.
The inner functions are now defined as ordinal methods, which are
accessible from tests.
Signed-off-by: Kazuyoshi Kato <katokazu@amazon.com>
Cory Snider