In general, it is not recommended to use TRAMP functions and variables not described in this manual. They might change their signature and/or semantics without any announcement.
Sometimes, it is not convenient to open a new connection to a remote
host, including entering the password and alike. For example, this is
nasty for packages providing file name completion. Such a package
could signal to TRAMP, that they don’t want it to establish a
new connection. Use the variable non-essential temporarily and
bind it to non-nil value.
(let ((non-essential t)) …)
Keeping a local cache of remote file attributes in sync with the remote host is a time-consuming operation. Flushing and re-querying these attributes can tax TRAMP to a grinding halt on busy remote hosts.
To get around these types of slow-downs in TRAMP’s
responsiveness, set the process-file-side-effects to nil
to stop TRAMP from flushing the cache. This is helpful in
situations where callers to process-file know there are no file
attribute changes. The let-bind form to accomplish this:
(let (process-file-side-effects) …)
For asynchronous processes, TRAMP uses a process sentinel to
flush file attributes cache. When callers to start-file-process
know beforehand no file attribute changes are expected, then the
process sentinel should be set to the default state. In cases where
the caller defines its own process sentinel, TRAMP’s process
sentinel is overwritten. The caller can still flush the file
attributes cache in its process sentinel with this code:
(unless (memq (process-status proc) '(run open)) (dired-uncache remote-directory))
Since TRAMP traverses subdirectories starting with the
root directory, it is most likely sufficient to make the
default-directory of the process buffer as the root directory.
Timers run asynchronously at any time when Emacs is waiting for
sending a string to a process, or waiting for process output. They
can run any remote file operation, which would conflict with the
already running remote file operation, if the same connection is
affected. TRAMP detects this situation, and raises the
remote-file-error error. A timer function should avoid this
situation. As a minimum, it should protect itself against this error, by
wrapping the timer function body as follows:
(ignore-error 'remote-file-error …)