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/*
* include/framework/scheduling/Epoch.h
*
* Copyright (C) 2023 Douglas B. Rumbaugh <drumbaugh@psu.edu>
*
* Distributed under the Modified BSD License.
*
*/
#pragma once
#include <condition_variable>
#include <mutex>
#include "framework/structure/MutableBuffer.h"
#include "framework/structure/ExtensionStructure.h"
#include "framework/structure/BufferView.h"
namespace de {
template <RecordInterface R, ShardInterface S, QueryInterface Q, LayoutPolicy L>
class Epoch {
private:
typedef MutableBuffer<R> Buffer;
typedef ExtensionStructure<R, S, Q, L> Structure;
typedef BufferView<R> BufView;
public:
Epoch(size_t number=0)
: m_buffer(nullptr)
, m_structure(nullptr)
, m_active_merge(false)
, m_active_jobs(0)
, m_active(true)
, m_epoch_number(number)
{}
Epoch(size_t number, Structure *structure, Buffer *buff)
: m_buffer(buff)
, m_structure(structure)
, m_active_jobs(0)
, m_active_merge(false)
, m_active(true)
, m_epoch_number(number)
{
structure->take_reference();
}
~Epoch() {
assert(m_active_jobs.load() == 0);
/* FIXME: this is needed to keep the destructor from
* sometimes locking up here. But there *shouldn't* be
* any threads waiting on this signal at object destruction,
* so something else is going on here that needs looked into
*/
//m_active_cv.notify_all();
if (m_structure) {
m_structure->release_reference();
}
}
void start_job() {
m_active_jobs.fetch_add(1);
}
void end_job() {
assert(m_active_jobs.load() > 0);
m_active_jobs.fetch_add(-1);
if (m_active_jobs.load() == 0) {
std::unique_lock<std::mutex> lk(m_cv_lock);
m_active_cv.notify_all();
}
}
size_t get_active_job_num() {
return m_active_jobs.load();
}
size_t get_epoch_number() {
return m_epoch_number;
}
Structure *get_structure() {
return m_structure;
}
BufView get_buffer() {
return m_buffer->get_buffer_view();
}
/*
* Returns a new Epoch object that is a copy of this one. The new object will also contain
* a copy of the m_structure, rather than a reference to the same one. The epoch number of
* the new epoch will be set to the provided argument.
*/
Epoch *clone(size_t number) {
std::unique_lock<std::mutex> m_buffer_lock;
auto epoch = new Epoch(number);
epoch->m_buffer = m_buffer;
if (m_structure) {
epoch->m_structure = m_structure->copy();
/* the copy routine returns a structure with 0 references */
epoch->m_structure->take_reference();
}
return epoch;
}
/*
* Check if a merge can be started from this Epoch.
* At present, without concurrent merging, this simply
* checks if there is currently a scheduled merge based
* on this Epoch. If there is, returns false. If there
* isn't, return true and set a flag indicating that
* there is an active merge.
*/
bool prepare_reconstruction() {
auto old = m_active_merge.load();
if (old) {
return false;
}
// FIXME: this needs cleaned up
while (!m_active_merge.compare_exchange_strong(old, true)) {
old = m_active_merge.load();
if (old) {
return false;
}
}
return true;
}
void set_inactive() {
m_active = false;
}
/*
*
*/
bool retirable() {
/* if epoch is currently active, then it cannot be retired */
if (m_active) {
return false;
}
/*
* if the epoch has active jobs but is not itself active,
* wait for them to finish and return true. If there are
* not active jobs, return true immediately
*/
std::unique_lock<std::mutex> lk(m_cv_lock);
while (m_active_jobs.load() > 0) {
m_active_cv.wait(lk);
}
return true;
}
bool advance_buffer_head(size_t head) {
return m_buffer->advance_head(head);
}
private:
Structure *m_structure;
Buffer *m_buffer;
std::condition_variable m_active_cv;
std::mutex m_cv_lock;
std::mutex m_buffer_lock;
std::atomic<bool> m_active_merge;
/*
* The number of currently active jobs
* (queries/merges) operating on this
* epoch. An epoch can only be retired
* when this number is 0.
*/
std::atomic<size_t> m_active_jobs;
bool m_active;
size_t m_epoch_number;
};
}
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