ClickHouse/dbms/include/DB/Common/AIO.h

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#pragma once
#include <DB/Common/Exception.h>
#include <common/logger_useful.h>
#include <common/singleton.h>
#include <Poco/Logger.h>
#include <boost/range/iterator_range.hpp>
#include <boost/noncopyable.hpp>
#include <condition_variable>
#include <future>
#include <mutex>
#include <map>
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#include <linux/aio_abi.h>
#include <sys/syscall.h>
#include <unistd.h>
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/** Небольшие обёртки для асинхронного ввода-вывода.
*/
inline int io_setup(unsigned nr, aio_context_t * ctxp)
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{
return syscall(__NR_io_setup, nr, ctxp);
}
inline int io_destroy(aio_context_t ctx)
{
return syscall(__NR_io_destroy, ctx);
}
/// last argument is an array of pointers technically speaking
inline int io_submit(aio_context_t ctx, long nr, struct iocb * iocbpp[])
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{
return syscall(__NR_io_submit, ctx, nr, iocbpp);
}
inline int io_getevents(aio_context_t ctx, long min_nr, long max_nr, io_event *events, struct timespec * timeout)
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{
return syscall(__NR_io_getevents, ctx, min_nr, max_nr, events, timeout);
}
struct AIOContext : private boost::noncopyable
{
aio_context_t ctx;
AIOContext(unsigned int nr_events = 128)
{
ctx = 0;
if (io_setup(nr_events, &ctx) < 0)
DB::throwFromErrno("io_setup failed");
}
~AIOContext()
{
io_destroy(ctx);
}
};
namespace DB
{
namespace ErrorCodes
{
extern const int AIO_COMPLETION_ERROR;
extern const int AIO_SUBMIT_ERROR;
}
class AIOContextPool : public Singleton<AIOContextPool>
{
friend class Singleton<AIOContextPool>;
static const auto max_concurrent_events = 128;
static const auto timeout_sec = 1;
AIOContext aio_context{max_concurrent_events};
using id_t = size_t;
using bytes_read_t = ssize_t;
/// Autoincremental id used to identify completed requests
id_t id{};
mutable std::mutex mutex;
mutable std::condition_variable have_resources;
std::map<id_t, std::promise<bytes_read_t>> promises;
std::atomic<bool> cancelled{false};
std::thread io_completion_monitor{&AIOContextPool::doMonitor, this};
~AIOContextPool()
{
cancelled.store(true, std::memory_order_relaxed);
io_completion_monitor.join();
}
void doMonitor()
{
/// continue checking for events unless cancelled
while (!cancelled.load(std::memory_order_relaxed))
waitForCompletion();
/// wait until all requests have been completed
while (!promises.empty())
waitForCompletion();
}
void waitForCompletion()
{
/// array to hold completion events
io_event events[max_concurrent_events];
try
{
const auto num_events = getCompletionEvents(events, max_concurrent_events);
fulfillPromises(events, num_events);
notifyProducers(num_events);
}
catch (...)
{
/// there was an error, log it, return to any producer and continue
reportExceptionToAnyProducer();
tryLogCurrentException("AIOContextPool::waitForCompletion()");
}
}
int getCompletionEvents(io_event events[], const int max_events)
{
timespec timeout{timeout_sec};
auto num_events = 0;
/// request 1 to `max_events` events
while ((num_events = io_getevents(aio_context.ctx, 1, max_events, events, &timeout)) < 0)
if (errno != EINTR)
throwFromErrno("io_getevents: Failed to wait for asynchronous IO completion",
ErrorCodes::AIO_COMPLETION_ERROR, errno);
return num_events;
}
void fulfillPromises(const io_event events[], const int num_events)
{
if (num_events == 0)
return;
const std::lock_guard<std::mutex> lock{mutex};
/// look at returned events and find corresponding promise, set result and erase promise from map
for (const auto & event : boost::make_iterator_range(events, events + num_events))
{
/// get id from event
const auto id = event.data;
/// set value via promise and release it
const auto it = promises.find(id);
if (it == std::end(promises))
{
LOG_CRITICAL(&Poco::Logger::get("AIOcontextPool"), "Found io_event with unknown id " << id);
continue;
}
it->second.set_value(event.res);
promises.erase(it);
}
}
void notifyProducers(const int num_producers) const
{
if (num_producers == 0)
return;
if (num_producers > 1)
have_resources.notify_all();
else
have_resources.notify_one();
}
void reportExceptionToAnyProducer()
{
const std::lock_guard<std::mutex> lock{mutex};
const auto any_promise_it = std::begin(promises);
any_promise_it->second.set_exception(std::current_exception());
}
public:
/// Request AIO read operation for iocb, returns a future with number of bytes read
std::future<bytes_read_t> post(struct iocb & iocb)
{
std::unique_lock<std::mutex> lock{mutex};
/// get current id and increment it by one
const auto request_id = id++;
/// create a promise and put request in "queue"
promises.emplace(request_id, std::promise<bytes_read_t>{});
/// store id in AIO request for further identification
iocb.aio_data = request_id;
auto num_requests = 0;
struct iocb * requests[] { &iocb };
/// submit a request
while ((num_requests = io_submit(aio_context.ctx, 1, requests)) < 0)
{
if (errno == EAGAIN)
/// wait until at least one event has been completed (or a spurious wakeup) and try again
have_resources.wait(lock);
else if (errno != EINTR)
throwFromErrno("io_submit: Failed to submit a request for asynchronous IO",
ErrorCodes::AIO_SUBMIT_ERROR, errno);
}
return promises[request_id].get_future();
}
};
}