1 stable release
1.0.0 | Jun 1, 2021 |
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#42 in #sleep
14KB
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lockpipes - a commitment-free alternative to sleep
What is this?
A LockPipe
is a named pipe used as a synchronization mechanism. lockpipes
is a library for using these, and lockpipe
is a CLI to the main parts of that library.
Why does this exist?
To keep one-shot DaemonSet
s on Kubernetes from restarting until I want them to.
Calling sleep
is a commitment. You're telling the system "don't schedule me for this long". To bail out early, you can either register signal handlers or loop over a shorter sleep interval.
With Kubernetes, there's also the terminationGracePeriodSeconds
(default 30) to consider. If the sleep interval is longer, then the grace period becomes how long it takes to restart a Pod
.
With a DaemonSet
and a modest number of nodes, this can lead to very long rolling restarts. This in turn makes incremental changes much more cumbersome.
In other contexts, blocking on reading from STDIN is an option. Kubernetes closes this stream though.
Creating a pipe and reading from it works, but then you need to deal with shutting it down.
This tool (and library, if you're into that sort of thing) has everything you need to manage this stuff.
How do I get this majestic tool?
$ cargo install lockpipes
How do I use it?
The lockpipe
command has a set of subcommands for each stage of the lifecycle (create -> read -> write -> delete).
Most of the time, you'll only need two commands: read
and write
. Both check if the pipe exists
and create
it if needed. Neither delete
s anything.
All subcommands accept a --path
argument, and read from the LOCKPIPE_PATH
environment variable. This specifies the path to use for the pipe.
For brevity, the examples below assume the following environment:
LOCKPIPE_PATH=example.pipe
LOCKPIPE_LOG_FILTER=debug
To read from the pipe (blocking if there are no writers), call read
:
$ lockpipe read
[DEBUG lockpipes] ensuring pipe exists at "example.pipe"
[INFO lockpipes] pipe exists at "example.pipe"
[DEBUG lockpipes] reading from pipe at "example.pipe"
To write to the pipe (blocking if there are no readers), call write
:
$ lockpipe write
[DEBUG lockpipes] ensuring pipe exists at "example.pipe"
[INFO lockpipes] pipe exists at "example.pipe"
[DEBUG lockpipes] writing to pipe at "example.pipe"
In the trivial case, it doesn't usually matter which end reads or writes. It only writes empty strings, and it discards all data read. For other scenarios, either may be more useful, such as waiting until something starts.
If you want to do complicated things, it may be helpful to handle some parts by hand.
Create a pipe with create
. Exits 0 if it creates a pipe or something exists at the given path. Exits non-zero if something went wrong.
$ lockpipe create
[DEBUG lockpipes] creating pipe at "example.pipe"
[INFO lockpipes] created pipe at "example.pipe"
Check if a pipe exists with exists
. The exit status will be 0 if the pipe exists, 1 if it does not, or some other non-zero value if something went wrong.
$ lockpipe exists
[DEBUG lockpipes] checking if pipe exists at "example.pipe"
[INFO lockpipes] pipe exists at "example.pipe"
Delete a pipe with delete
. Exits 0 if it deletes something (or nothing exists) at the given path. Exits non-zero if something went wrong.
$ lockpipe delete
[INFO lockpipes] deleted pipe at "example.pipe"
Other Exit Statuses
In each case, if something went wrong, the exit status should correspond to some errno
value. The particular value depends on platform and problem. It also logs an error
with a more readable interpretation of the problem.
Environment Variables
Name | Default Value | Examples | Description |
---|---|---|---|
LOCKPIPE_PATH | /run/forever | /path/to/lock.pipe | Sets path to the pipe |
LOCKPIPE_LOG_FILTER | info | error, warn, info, debug, trace. | Configures log filtering |
LOCKPIPE_LOG_STYLE | auto | auto, always, never. | Configures log styling |
License
lockpipes
is available under the MIT License, see LICENSE.txt
for the full text.
Dependencies
~7–16MB
~195K SLoC