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// Copyright 2017 Yahoo Inc. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
#pragma once
#include <vespa/document/base/globalid.h>
#include <vespa/vespalib/stllike/hash_set.h>
#include <utility>
namespace document {
class DocumentId;
}
namespace storage::distributor {
class OperationSequencer;
/**
* Represents a move-only handle which effectively holds a guard for
* allowing sequenced operations towards a particular document ID.
*
* Destroying a handle will implicitly release the guard, allowing
* new sequenced operations towards the ID.
*/
class SequencingHandle {
OperationSequencer* _sequencer;
document::GlobalId _gid;
public:
SequencingHandle() : _sequencer(nullptr) {}
SequencingHandle(OperationSequencer& sequencer, const document::GlobalId& gid)
: _sequencer(&sequencer),
_gid(gid)
{
}
~SequencingHandle() {
release();
}
SequencingHandle(const SequencingHandle&) = delete;
SequencingHandle& operator=(const SequencingHandle&) = delete;
SequencingHandle(SequencingHandle&& rhs) noexcept
: _sequencer(rhs._sequencer),
_gid(rhs._gid)
{
rhs._sequencer = nullptr;
}
SequencingHandle& operator=(SequencingHandle&& rhs) noexcept {
if (&rhs != this) {
std::swap(_sequencer, rhs._sequencer);
std::swap(_gid, rhs._gid);
}
return *this;
}
bool valid() const noexcept { return (_sequencer != nullptr); }
const document::GlobalId& gid() const noexcept { return _gid; }
void release();
};
/**
* An operation sequencer allows for efficiently checking if an operation is
* already pending for a given document ID (with very high probability; false
* positives are possible, but false negatives are not).
*
* When a SequencingHandle is acquired for a given ID, no further valid handles
* can be acquired for that ID until the original handle has been destroyed.
*/
class OperationSequencer {
using GidSet = vespalib::hash_set<document::GlobalId, document::GlobalId::hash>;
GidSet _active_gids;
friend class SequencingHandle;
public:
OperationSequencer();
~OperationSequencer();
// Returns a handle with valid() == true iff no concurrent operations are
// already active for `id`.
SequencingHandle try_acquire(const document::DocumentId& id);
private:
void release(const SequencingHandle& handle);
};
} // storage::distributor
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