propagating many messages from a fast store (typically maildir or a
local IMAP server) to a slow asynchronous store could cause gigabytes of
data being buffered. avoid this by throttling fetches if the target
context reports memory usage above a configurable limit.
REFMAIL: 9737edb14457c71af4ed156c1be0ae59@mpcjanssen.nl
don't try to lock it until we actually read or write it.
the idea is to not fail with SyncState * if we tried to load the state
before selecting a non-existing mailbox. this is ok, because if the
mailbox is missing, we obviously have no sync state pertaining to it,
either.
as a side effect, this allows simplifying an error path.
the seznam.cz IMAP server seems very eager to send UIDNEXT responses
despite not supporting UIDPLUS. this doesn't appear to be a particularly
sensible combination, but it's valid nonetheless.
however, that means that we need to save the UIDNEXT value before we
start storing messages, lest imap_find_new_msgs() will simply overlook
them. we do that outside the driver, in an already present field - this
actually makes the main path more consistent with the journal recovery
path.
analysis by Tomas Tintera <trosos@seznam.cz>.
REFMAIL: 20141220215032.GA10115@kyvadlo.trosos.seznam.cz
... for windows fs compatibility.
the maildir-specific InfoDelimiter inherits the global FieldDelimiter
(which affects SyncState), based on the assumption that if the sync
state is on a windows FS, the mailboxes certainly will be as well, while
the inverse is not necessarily true (when running on unix, anyway).
REFMAIL: <CA+m_8J1ynqAjHRJagvKt9sb31yz047Q7NH-ODRmHOKyfru8vtA@mail.gmail.com>
memcmp() is unfortunately not guaranteed to read forward byte-by-byte,
which means that the clever use as a strncmp() without the pointless
strlen()s is not permitted, and can actually misbehave with
SSE-optimized string functions.
so implement proper equals() and starts_with() functions. as a bonus,
the calls are less cryptic.
a failure here is rather unlikely, but let's be pedantic.
a failure is not fatal (we'll just enter the journal replay path next
time), so only print warnings.
found by coverity.
we would try to print the uids from the non-existing srec of unpaired
messages while preparing expiration.
this would happen only if a) MaxMessages was configured and b) new
messages appeared on the slave but we were not pushing, so it's a bit of
a corner case.
found by coverity.
by putting the message propagation last, d3f634702 uncovered a
long-standing problem: we might have closed the source store before all
messages were propagated from it.
msgs_copied() was not checked at all, and msgs_flags_set() was doing it
wrong (sync_close() was not checked).
instead of trying to fix/extend the msgs_flags_set() model (ref-counting
and cancelation checking in lower-level functions, and return values to
propagate the status), place the refs/derefs around higher-level scopes
and do the checking only there. this is effectively simpler, and does
away with some obscure macros.
as we now don't actually start propagating new messages until all TUIDs
have been generated, it's sufficient to sync just once. this makes it
a cheap operation, so we can do it at SYNC_NORMAL level already.
i.e., move it back. whatever the original reason was, it's now gone.
this order is way more natural, which allows us to remove the osrecadd
and S_DONE hacks.
this helps enormously on the first sync of a 100k message box with a
limit of 1k messages. it also happens to make the syncing idempotent.
in a few conditionals we now explicitly test for max_messages being
enabled, not smaxxuid != 0, as after the initial fetch with no important
messages smaxxuid is zero, but we still have to skip over 99k messages
in the above case.
previous sequence:
examine & propagate new => examine old => propagate old
new sequence:
examine new => examine old => propagate new => propagate old
this alone does not buy us much ...
we can bump the internal variable whereever convenient, but we cannot
log it until we know that all messages were copied, as otherwise we
could miss some new messages after an interruption. with the new
approach, interruption would merely cause some additonal traffic.
less code duplication, more logical order of issued driver commands
(especially after the next commit), and the "side effect" of letting the
message expiration code see those deletions if they are asynchronous.
the delay optimized the corner case of previously important but now
expired messages on the slave disappearing, either through an external
expunge or after a journal replay. no point in pessimizing the common
case.
the removed code would only ever trigger if a) we were after a journal
replay or b) something external expunged the expired messages - both are
corner cases not worth the extra code.
however, this means that the syncing code further down now needs to take
care of these zombies.
in the end, the normal cleanup will take care of all expired entries,
new and old.
that is, don't count them towards the total only below the cut-off
point. making them extend the working set even though they are inside it
is counterintuitive.
while maildir has a clearly defined meaning of "recent" and for example
mutt handles it graciously, IMAP's definition is fubared to the point
that some servers (for example gmail) simply refuse to support it.
for symmetry reasons it is best to pretend that it doesn't exist at all.
it doesn't seem too useful anyway (the user can simply mark the messages
as read to allow pruning).
and last but not least, the man page of mbsync says nothing about
"recent", only "unread". unlike the isync man page, though.
even if we are not propagating new messages, the appearance of new
messages on the slave can lead to expiring older messages. for that, we
need to know their importance, and thus flags.
the alternative would be not doing an expiration run when not fetching
new messages, but that would mean more conditionals all over the place.
as the decision is somewhat arbitrary, just do the simpler thing.
Oswald Buddenhagen