discourse/spec/lib/distributed_mutex_spec.rb

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# frozen_string_literal: true
RSpec.describe DistributedMutex do
before { DistributedMutex.any_instance.stubs(:sleep) }
let(:key) { "test_mutex_key" }
after { Discourse.redis.del(key) }
it "allows only one mutex object to have the lock at a time" do
mutexes = (1..10).map { DistributedMutex.new(key, redis: DiscourseRedis.new) }
x = 0
mutexes
.map do |m|
Thread.new do
m.synchronize do
y = x
sleep 0.001
x = y + 1
end
end
end
.map(&:join)
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expect(x).to eq(10)
end
it "handles auto cleanup correctly" do
m = DistributedMutex.new(key)
Discourse.redis.setnx key, Time.now.to_i - 1
start = Time.now
m.synchronize { "nop" }
# no longer than a second
expect(Time.now).to be <= start + 1
end
it "allows the validity of the lock to be configured" do
mutex = DistributedMutex.new(key, validity: 2)
mutex.synchronize do
expect(Discourse.redis.ttl(key)).to be <= 3
expect(Discourse.redis.get(key).to_i).to be_within(1.second).of(Time.now.to_i + 2)
end
mutex = DistributedMutex.new(key)
mutex.synchronize do
expect(Discourse.redis.ttl(key)).to be <= DistributedMutex::DEFAULT_VALIDITY + 1
expect(Discourse.redis.get(key).to_i).to be_within(1.second).of(
Time.now.to_i + DistributedMutex::DEFAULT_VALIDITY,
)
end
end
it "maintains mutex semantics" do
m = DistributedMutex.new(key)
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expect { m.synchronize { m.synchronize {} } }.to raise_error(ThreadError)
end
describe "readonly redis" do
before { Discourse.redis.slaveof "127.0.0.1", "65534" }
after { Discourse.redis.slaveof "no", "one" }
it "works even if redis is in readonly" do
m = DistributedMutex.new(key)
start = Time.now
done = false
expect { m.synchronize { done = true } }.to raise_error(Discourse::ReadOnly)
expect(done).to eq(false)
expect(Time.now).to be <= start + 1
end
end
describe "executions" do
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it "should not allow critical sections to overlap" do
connections = 3.times.map { DiscourseRedis.new }
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scenario =
Concurrency::Scenario.new do |execution|
locked = false
Discourse.redis.del("mutex_key")
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connections.each { |connection| connection.unwatch }
3.times do |i|
execution.spawn do
begin
redis = Concurrency::RedisWrapper.new(connections[i], execution)
2.times do
DistributedMutex.synchronize("mutex_key", redis: redis) do
raise "already locked #{execution.path}" if locked
locked = true
execution.yield
raise "already unlocked #{execution.path}" unless locked
locked = false
end
end
rescue Redis::ConnectionError
end
end
end
end
scenario.run(runs: 10)
end
end
end