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/**
* Copyright (C) 2018-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the Server Side Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#pragma once
#include <memory>
#include <vector>
#include "mongo/client/read_preference.h"
#include "mongo/db/shard_id.h"
#include "mongo/executor/task_executor.h"
#include "mongo/executor/task_executor_pool.h"
#include "mongo/s/client/shard.h"
#include "mongo/util/concurrency/mutex.h"
#include "mongo/util/future.h"
#include "mongo/util/time_support.h"
namespace mongo {
using OperationContextFn = std::function<void(OperationContext*)>;
namespace txn {
/**
* This class groups all the asynchronous work scheduled by a given TransactionCoordinatorDriver.
*/
class AsyncWorkScheduler {
public:
AsyncWorkScheduler(ServiceContext* serviceContext);
~AsyncWorkScheduler();
/**
* @brief Returns a shared pointer to the executor
*/
ExecutorPtr getExecutor() {
return _executor;
}
/**
* Schedules the specified callable to execute asynchronously and returns a future which will be
* set with its result.
*/
template <class Callable>
Future<FutureContinuationResult<Callable, OperationContext*>> scheduleWork(
Callable&& task) noexcept {
return scheduleWorkIn(Milliseconds(0), std::forward<Callable>(task));
}
template <class Callable>
Future<FutureContinuationResult<Callable, OperationContext*>> scheduleWorkIn(
Milliseconds millis, Callable&& task) noexcept {
return scheduleWorkAt(_executor->now() + millis, std::forward<Callable>(task));
}
template <class Callable>
Future<FutureContinuationResult<Callable, OperationContext*>> scheduleWorkAt(
Date_t when, Callable&& task) noexcept {
using ReturnType = FutureContinuationResult<Callable, OperationContext*>;
auto pf = makePromiseFuture<ReturnType>();
auto taskCompletionPromise = std::make_shared<Promise<ReturnType>>(std::move(pf.promise));
try {
stdx::unique_lock<Latch> ul(_mutex);
uassertStatusOK(_shutdownStatus);
auto scheduledWorkHandle = uassertStatusOK(_executor->scheduleWorkAt(
when,
[this, task = std::forward<Callable>(task), taskCompletionPromise](
const executor::TaskExecutor::CallbackArgs& args) mutable noexcept {
taskCompletionPromise->setWith([&] {
{
stdx::lock_guard lk(_mutex);
uassertStatusOK(_shutdownStatus);
uassertStatusOK(args.status);
}
ThreadClient tc("TransactionCoordinator", _serviceContext);
auto uniqueOpCtxIter = [&] {
stdx::lock_guard lk(_mutex);
return _activeOpContexts.emplace(_activeOpContexts.begin(),
tc->makeOperationContext());
}();
ON_BLOCK_EXIT([&] {
stdx::lock_guard lk(_mutex);
_activeOpContexts.erase(uniqueOpCtxIter);
// There is no need to call _notifyAllTasksComplete here, because we
// will still have an outstanding _activeHandles entry, so the scheduler
// is never completed at this point
});
return task(uniqueOpCtxIter->get());
});
}));
auto it =
_activeHandles.emplace(_activeHandles.begin(), std::move(scheduledWorkHandle));
ul.unlock();
return std::move(pf.future).tapAll(
[this, it = std::move(it)](StatusOrStatusWith<ReturnType> s) {
stdx::lock_guard<Latch> lg(_mutex);
_activeHandles.erase(it);
_notifyAllTasksComplete(lg);
});
} catch (const DBException& ex) {
taskCompletionPromise->setError(ex.toStatus());
return std::move(pf.future);
}
}
/**
* Sends a command asynchronously to the given shard and returns a Future when that request
* completes (with error or not).
*/
Future<executor::TaskExecutor::ResponseStatus> scheduleRemoteCommand(
const ShardId& shardId,
const ReadPreferenceSetting& readPref,
const BSONObj& commandObj,
OperationContextFn operationContextFn = [](OperationContext*) {});
/**
* Allows sub-tasks on this scheduler to be grouped together and works-around the fact that
* futures are not cancellable.
*
* Shutting down the returned child scheduler has no effect on the parent. Shutting down the
* parent scheduler also shuts down all child schedulers and prevents new ones from starting.
*/
std::unique_ptr<AsyncWorkScheduler> makeChildScheduler();
/**
* Non-blocking method, which interrupts all currently active scheduled commands or tasks and
* prevents any new ones from starting.
* After this method is called, all returned futures, which haven't yet been signalled will be
* set to the specified status. Attempting to schedule any new operations will return ready
* futures set to the specified status.
*
* Must not be called with Status::OK.
*/
void shutdown(Status status);
/**
* Blocking call, which will wait until any scheduled commands/tasks and child schedulers have
* drained.
*
* It is allowed to be called without calling shutdown, but in that case it the caller's
* responsibility to ensure that no new work gets scheduled.
*/
void join();
private:
using ChildIteratorsList = std::list<AsyncWorkScheduler*>;
// A targeted host and the shard object used to target it. The shard object is passed through
// resolved so the caller can avoid a potentially blocking "ShardRegistry::getShard" call.
struct HostAndShard {
HostAndPort hostTargeted;
std::shared_ptr<Shard> shard;
};
/**
* Finds the host and port for a shard id, returning it and the shard object used for targeting.
*/
Future<HostAndShard> _targetHostAsync(
const ShardId& shardId,
const ReadPreferenceSetting& readPref,
OperationContextFn operationContextFn = [](OperationContext*) {});
/**
* Returns true when all the registered child schedulers, op contexts and handles have joined.
*/
bool _quiesced(WithLock) const;
/**
* Invoked every time a registered op context, handle or child scheduler is getting
* unregistered. Used to notify the 'all lists empty' condition variable when there is no more
* activity on a scheduler which has been shut down.
*/
void _notifyAllTasksComplete(WithLock);
// Service context under which this executor runs
ServiceContext* const _serviceContext;
// Executor for performing async tasks.
std::shared_ptr<executor::TaskExecutor> _executor;
// If this work scheduler was constructed through 'makeChildScheduler', points to the parent
// scheduler and contains the iterator from the parent, which needs to be removed on destruction
AsyncWorkScheduler* _parent{nullptr};
ChildIteratorsList::iterator _itToRemove;
// Mutex to protect the shared state below
Mutex _mutex = MONGO_MAKE_LATCH("AsyncWorkScheduler::_mutex");
// If shutdown() is called, this contains the first status that was passed to it and is an
// indication that no more operations can be scheduled
Status _shutdownStatus{Status::OK()};
// Any active scheduled work will have its operation context stored here
std::list<ServiceContext::UniqueOperationContext> _activeOpContexts;
// Any active scheduled work or network operation will have its TaskExecutor handle stored here
std::list<executor::TaskExecutor::CallbackHandle> _activeHandles;
// Any outstanding child schedulers created though 'makeChildScheduler'
ChildIteratorsList _childSchedulers;
// Notified when the the scheduler is shut down and the last active handle, operation context or
// child scheduler has been unregistered.
stdx::condition_variable _allListsEmptyCV;
};
ShardId getLocalShardId(ServiceContext* service);
enum class ShouldStopIteration { kYes, kNo };
/**
* Helper function that allows you to asynchronously aggregate the results of a vector of Futures.
* It's essentially an async foldLeft.
*
* The combiner function specifies how to take an incoming result (the second parameter) and combine
* it to create the final ('global') result (the first parameter). The inital value for the 'global
* result' is specified by initValue.
*
* Example from the unit tests:
*
* TEST_F(TransactionCoordinatorTest, CollectReturnsCombinedResultWithSeveralInputFutures) {
* std::vector<Future<int>> futures;
* std::vector<Promise<int>> promises;
* std::vector<int> futureValues;
* for (int i = 0; i < 5; ++i) {
* auto pf = makePromiseFuture<int>();
* futures.push_back(std::move(pf.future));
* promises.push_back(std::move(pf.promise));
* futureValues.push_back(i);
* }
*
* // Sum all of the inputs.
* auto resultFuture = collect<int, int>(futures, 0, [](int& result, const int& next) {
* result += next;
* return true;
* });
*
* for (size_t i = 0; i < promises.size(); ++i) {
* promises[i].emplaceValue(futureValues[i]);
* }
*
* // Result should be the sum of all the values emplaced into the promises.
* ASSERT_EQ(resultFuture.get(), std::accumulate(futureValues.begin(), futureValues.end(), 0));
* }
*
*/
template <class IndividualResult, class GlobalResult, class Callable>
Future<GlobalResult> collect(std::vector<Future<IndividualResult>>&& futures,
GlobalResult&& initValue,
Callable&& combiner) {
if (futures.size() == 0) {
return initValue;
}
/**
* Shared state for the continuations of the individual futures in the array.
*/
struct SharedBlock {
SharedBlock(size_t numOutstandingResponses,
GlobalResult globalResult,
Promise<GlobalResult> resultPromise,
Callable&& combiner)
: numOutstandingResponses(numOutstandingResponses),
globalResult(std::move(globalResult)),
resultPromise(std::move(resultPromise)),
combiner(std::move(combiner)) {}
/*****************************************************
* The first few fields have fixed values. *
******************************************************/
// Protects all state in the SharedBlock.
Mutex mutex = MONGO_MAKE_LATCH("SharedBlock::mutex");
// If any response returns an error prior to a response setting shouldStopIteration to
// ShouldStopIteration::kYes, the promise will be set with that error rather than the global
// result.
Status status{Status::OK()};
// If the combiner returns kYes after processing any response, the combiner will not be
// applied to any further responses.
ShouldStopIteration shouldStopIteration{ShouldStopIteration::kNo};
/*****************************************************
* The below have initial values based on user input.*
******************************************************/
// The number of input futures that have not yet been resolved and processed.
size_t numOutstandingResponses;
// The variable where the intermediate results and final result is stored.
GlobalResult globalResult;
// The promise to be fulfilled when the result is ready.
Promise<GlobalResult> resultPromise;
// The input combiner function.
Callable combiner;
};
// Create the promise and future used to fulfill the result.
auto resultPromiseAndFuture = makePromiseFuture<GlobalResult>();
// Create the shared context used by all continuations
auto sharedBlock = std::make_shared<SharedBlock>(futures.size(),
std::move(initValue),
std::move(resultPromiseAndFuture.promise),
std::move(combiner));
// For every input future, add a continuation that will asynchronously update the
// SharedBlock upon completion of the input future.
for (auto&& localFut : futures) {
std::move(localFut)
.then([sharedBlock](IndividualResult res) {
stdx::unique_lock<Latch> lk(sharedBlock->mutex);
if (sharedBlock->shouldStopIteration == ShouldStopIteration::kNo &&
sharedBlock->status.isOK()) {
sharedBlock->shouldStopIteration =
sharedBlock->combiner(sharedBlock->globalResult, std::move(res));
}
})
.onError([sharedBlock](Status s) {
stdx::unique_lock<Latch> lk(sharedBlock->mutex);
if (sharedBlock->shouldStopIteration == ShouldStopIteration::kNo &&
sharedBlock->status.isOK()) {
sharedBlock->status = s;
}
})
.getAsync([sharedBlock](Status s) {
stdx::unique_lock<Latch> lk(sharedBlock->mutex);
sharedBlock->numOutstandingResponses--;
if (sharedBlock->numOutstandingResponses == 0) {
// Unlock before emplacing the result in case any continuations do expensive
// work.
lk.unlock();
if (sharedBlock->status.isOK()) {
sharedBlock->resultPromise.emplaceValue(sharedBlock->globalResult);
} else {
sharedBlock->resultPromise.setError(sharedBlock->status);
}
}
});
}
return std::move(resultPromiseAndFuture.future);
}
/**
* Returns a future that will be resolved when all of the input futures have resolved, or rejected
* when any of the futures is rejected.
*/
Future<void> whenAll(std::vector<Future<void>>& futures);
/**
* Executes a function returning a Future until the function does not return an error status or
* until one of the provided error codes is returned.
*/
template <class LoopBodyFn, class ShouldRetryFn>
Future<FutureContinuationResult<LoopBodyFn>> doWhile(AsyncWorkScheduler& scheduler,
boost::optional<Backoff> backoff,
ShouldRetryFn&& shouldRetryFn,
LoopBodyFn&& f) {
using ReturnType = typename decltype(f())::value_type;
auto future = f();
return std::move(future).onCompletion(
[&scheduler,
backoff = std::move(backoff),
shouldRetryFn = std::forward<ShouldRetryFn>(shouldRetryFn),
f = std::forward<LoopBodyFn>(f)](StatusOrStatusWith<ReturnType> s) mutable {
if (!shouldRetryFn(s))
return Future<ReturnType>(std::move(s));
// Retry after a delay.
const auto delayMillis = (backoff ? backoff->nextSleep() : Milliseconds(0));
return scheduler.scheduleWorkIn(delayMillis, [](OperationContext* opCtx) {})
.then([&scheduler,
backoff = std::move(backoff),
shouldRetryFn = std::move(shouldRetryFn),
f = std::move(f)]() mutable {
return doWhile(
scheduler, std::move(backoff), std::move(shouldRetryFn), std::move(f));
});
});
}
} // namespace txn
} // namespace mongo
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