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// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
#pragma once
#include "rendezvous.h"
namespace vespalib {
/**
* Utility used to direct multi-threaded merging of 2 separate sources
* of information. Each thread calls the dualMerge function with its
* own thread id and sources. The first source of each thread is
* ultimately merged into the first source of thread 0. The second
* sources are handled the same way and the result ends up in the
* second source of thread 0. The sources may be of different
* types. Note that the dualMerge function will return when the
* director no longer needs the calling thread. In order to wait for
* the completion of the overall merge operation, external
* synchronization is needed.
**/
class DualMergeDirector
{
public:
struct Source {
virtual void merge(Source &rhs) = 0;
virtual ~Source() {}
};
private:
struct TaggedSource {
size_t thread_id;
Source *source;
TaggedSource(size_t t, Source &s) : thread_id(t), source(&s) {}
TaggedSource() : thread_id(-1), source(0) {}
};
struct MergeState {
enum State { MIXED, TYPEA, TYPEB, LAST, EMPTY } state;
TaggedSource first;
TaggedSource second;
MergeState() : state(EMPTY), first(), second() {}
MergeState(State s, const TaggedSource &a)
: state(s), first(a), second() {}
MergeState(State s, const TaggedSource &a, const TaggedSource &b)
: state(s), first(a), second(b) {}
bool merge();
};
struct MixedMergeStateExchanger : Rendezvous<MergeState, MergeState> {
bool last;
MixedMergeStateExchanger(bool v) :
Rendezvous<MergeState, MergeState>(2), last(v) {}
void mingle() override;
};
struct MergeStateExchanger : Rendezvous<MergeState, MergeState> {
size_t remaining;
MergeStateExchanger(size_t r) :
Rendezvous<MergeState, MergeState>(2), remaining(r) {}
void mingle() override;
};
size_t _num_threads;
MixedMergeStateExchanger _mixedExchanger;
MergeStateExchanger _typeAExchanger;
MergeStateExchanger _typeBExchanger;
public:
DualMergeDirector(size_t num_threads);
~DualMergeDirector();
void dualMerge(size_t thread_id, Source &typeA, Source &typeB);
};
} // namespace vespalib
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