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Move promotion logic inside workers #38
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Original file line number | Diff line number | Diff line change |
---|---|---|
@@ -1,4 +1,4 @@ | ||
FROM ruby:3.1 | ||
FROM ruby:3.2 | ||
RUN apt-get update -y && apt-get install -y ragel socat netcat smem apache2-utils | ||
WORKDIR /app | ||
CMD [ "bash" ] |
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Original file line number | Diff line number | Diff line change |
---|---|---|
@@ -0,0 +1,51 @@ | ||
require 'tempfile' | ||
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module Pitchfork | ||
class Flock | ||
Error = Class.new(StandardError) | ||
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def initialize(name) | ||
@name = name | ||
@file = Tempfile.create([name, '.lock']) | ||
@file.write("#{Process.pid}\n") | ||
@file.flush | ||
@owned = false | ||
end | ||
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def at_fork | ||
@owned = false | ||
@file.close | ||
@file = File.open(@file.path, "w") | ||
nil | ||
end | ||
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def unlink | ||
File.unlink(@file.path) | ||
rescue Errno::ENOENT | ||
false | ||
end | ||
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def try_lock | ||
raise Error, "Pitchfork::Flock(#{@name}) trying to lock an already owned lock" if @owned | ||
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if @file.flock(File::LOCK_EX | File::LOCK_NB) | ||
@owned = true | ||
else | ||
false | ||
end | ||
end | ||
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def unlock | ||
raise Error, "Pitchfork::Flock(#{@name}) trying to unlock a non-owned lock" unless @owned | ||
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begin | ||
if @file.flock(File::LOCK_UN) | ||
@owned = false | ||
true | ||
else | ||
false | ||
end | ||
end | ||
end | ||
end | ||
end |
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For my own knowledge:
Original problem: Using a POSIX mutex was problematic because if the process holding the mutex died, it wouldn't unlock, and would deadlock the promotion flow thereafter.
Solution: A file lock solves this problem because the lock against the file is automatically released by the OS when the process terminates?
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Yeah, I explored several approach to IPC mutexes.
First to use a
pthread_mutex_t
inside a shared memory page. And as you point out it wouldn't cleanup on exit, which in a context where we might SIGKILL processes ourselves is not OK.Then I tried sysV semaphores, they do have automatic cleanup, and we already use them via
semian
, but the API is very wonky to use, especially if you are trying to implement a mutex.In the end I figured
flock
was the least worse. It's already available in ruby core, no need for more C, the only downsides are:But overall it seems to work well.