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58 lines
1.9 KiB
C++
58 lines
1.9 KiB
C++
#pragma once
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#include <zkutil/Common.h>
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#include <string>
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#include <functional>
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namespace zkutil
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{
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/// Implementation of a distributed single barrier for ZooKeeper.
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/// Consider a barrier with N slots. A node that wants to enter this barrier
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/// creates a uniquely identified token and puts it in a free slot, then waits
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/// until all of the N slots have been taken.
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/// This implementation allows entering a barrier more than once. This is done
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/// by prefixing tokens with a tag which is an integer number representing the
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/// number of times this barrier has already been crossed. When a node attempts
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/// to puts its token into a slot, first it looks for lingering obsolete tokens,
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/// then, if found, deletes them. If a node has put its token into the last free
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/// slot, it increments the tag value.
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class SingleBarrier final
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{
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public:
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using CancellationHook = std::function<void()>;
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public:
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SingleBarrier(GetZooKeeper get_zookeeper_, const std::string & path_, size_t counter_);
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SingleBarrier(const SingleBarrier &) = delete;
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SingleBarrier & operator=(const SingleBarrier &) = delete;
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SingleBarrier(SingleBarrier &&) = default;
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SingleBarrier & operator=(SingleBarrier &&) = default;
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/// Register a function that cancels barrier operations if requested.
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void setCancellationHook(CancellationHook cancellation_hook_);
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void enter(UInt64 timeout = 0);
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private:
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/// Cancel any ongoing operation if requested. Additionally perform cleanup.
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void abortIfRequested();
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private:
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/// Helper that acquires an alive ZooKeeper session.
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GetZooKeeper get_zookeeper;
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EventPtr event = std::make_shared<Poco::Event>();
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/// Function that cancels barrier operations if requested.
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CancellationHook cancellation_hook;
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/// Path to the barrier storage.
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std::string path;
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/// Token created by the node attempting to enter the barrier.
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std::string token;
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/// Number of available slots.
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size_t counter;
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};
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}
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