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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 <functional>
#include "mongo/base/status.h"
#include "mongo/bson/bsonobjbuilder.h"
#include "mongo/db/client.h"
#include "mongo/db/service_context.h"
#include "mongo/platform/bitwise_enum_operators.h"
#include "mongo/transport/service_entry_point.h"
#include "mongo/transport/session.h"
#include "mongo/transport/transport_mode.h"
#include "mongo/util/duration.h"
#include "mongo/util/functional.h"
#include "mongo/util/out_of_line_executor.h"
namespace mongo {
namespace transport {
/*
* This is the interface for all ServiceExecutors.
*/
class ServiceExecutor : public OutOfLineExecutor {
public:
virtual ~ServiceExecutor() = default;
using Task = unique_function<void()>;
enum ScheduleFlags {
// No flags (kEmptyFlags) specifies that this is a normal task and that the executor should
// launch new threads as needed to run the task.
kEmptyFlags = 1 << 0,
// Deferred tasks will never get a new thread launched to run them.
kDeferredTask = 1 << 1,
// MayRecurse indicates that a task may be run recursively.
kMayRecurse = 1 << 2,
// MayYieldBeforeSchedule indicates that the executor may yield on the current thread before
// scheduling the task.
kMayYieldBeforeSchedule = 1 << 3,
};
/*
* Starts the ServiceExecutor. This may create threads even if no tasks are scheduled.
*/
virtual Status start() = 0;
/*
* Schedules a task with the ServiceExecutor and returns immediately.
*
* This is guaranteed to unwind the stack before running the task, although the task may be
* run later in the same thread.
*
* If defer is true, then the executor may defer execution of this Task until an available
* thread is available.
*/
virtual Status scheduleTask(Task task, ScheduleFlags flags) = 0;
/*
* Provides an executor-friendly wrapper for "scheduleTask". Internally, it wraps instance of
* "OutOfLineExecutor::Task" inside "ServiceExecutor::Task" objects, which are then scheduled
* for execution on the service executor. May throw if "scheduleTask" returns a non-okay status.
*/
void schedule(OutOfLineExecutor::Task func) override {
internalAssert(scheduleTask([task = std::move(func)]() mutable { task(Status::OK()); },
ScheduleFlags::kEmptyFlags));
}
/*
* Awaits the availability of incoming data for the specified session. On success, it will
* schedule the callback on current executor. Otherwise, it will invoke the callback with a
* non-okay status on the caller thread.
*/
virtual void runOnDataAvailable(Session* session,
OutOfLineExecutor::Task onCompletionCallback) = 0;
/*
* Stops and joins the ServiceExecutor. Any outstanding tasks will not be executed, and any
* associated callbacks waiting on I/O may get called with an error code.
*
* This should only be called during server shutdown to gracefully destroy the ServiceExecutor
*/
virtual Status shutdown(Milliseconds timeout) = 0;
/*
* Returns if this service executor is using asynchronous or synchronous networking.
*/
virtual Mode transportMode() const = 0;
/*
* Appends statistics about task scheduling to a BSONObjBuilder for serverStatus output.
*/
virtual void appendStats(BSONObjBuilder* bob) const = 0;
};
/**
* ServiceExecutorContext determines which ServiceExecutor is used for each Client.
*/
class ServiceExecutorContext {
public:
enum ThreadingModel {
kBorrowed,
kDedicated,
};
/**
* Get a pointer to the ServiceExecutorContext for a given client.
*
* This function is valid to invoke either on the Client thread or with the Client lock.
*/
static ServiceExecutorContext* get(Client* client) noexcept;
/**
* Set the ServiceExecutorContext for a given client.
*
* This function may only be invoked once and only while under the Client lock.
*/
static void set(Client* client, ServiceExecutorContext seCtx) noexcept;
/**
* Reset the ServiceExecutorContext for a given client.
*
* This function may only be invoked once and only while under the Client lock.
*/
static void reset(Client* client) noexcept;
ServiceExecutorContext() = default;
ServiceExecutorContext(const ServiceExecutorContext&) = delete;
ServiceExecutorContext& operator=(const ServiceExecutorContext&) = delete;
ServiceExecutorContext(ServiceExecutorContext&& seCtx)
: _client{std::exchange(seCtx._client, nullptr)},
_sep{std::exchange(seCtx._sep, nullptr)},
_threadingModel{seCtx._threadingModel},
_canUseReserved{seCtx._canUseReserved} {}
ServiceExecutorContext& operator=(ServiceExecutorContext&& seCtx) {
_client = std::exchange(seCtx._client, nullptr);
_sep = std::exchange(seCtx._sep, nullptr);
_threadingModel = seCtx._threadingModel;
_canUseReserved = seCtx._canUseReserved;
return *this;
}
/**
* Set the ThreadingModel for the associated Client's service execution.
*
* This function is only valid to invoke with the Client lock or before the Client is set.
*/
void setThreadingModel(ThreadingModel threadingModel) noexcept;
/**
* Set if reserved resources are available for the associated Client's service execution.
*
* This function is only valid to invoke with the Client lock or before the Client is set.
*/
void setCanUseReserved(bool canUseReserved) noexcept;
/**
* Get the ThreadingModel for the associated Client.
*
* This function is valid to invoke either on the Client thread or with the Client lock.
*/
auto getThreadingModel() const noexcept {
return _threadingModel;
}
/**
* Get an appropriate ServiceExecutor given the current parameters.
*
* This function is only valid to invoke from the associated Client thread. This function does
* not require the Client lock since all writes must also happen from that thread.
*/
ServiceExecutor* getServiceExecutor() noexcept;
private:
friend StringData toString(ThreadingModel threadingModel);
Client* _client = nullptr;
ServiceEntryPoint* _sep = nullptr;
ThreadingModel _threadingModel = ThreadingModel::kDedicated;
bool _canUseReserved = false;
bool _hasUsedSynchronous = false;
};
/**
* A small statlet for tracking which executors may be in use.
*/
class ServiceExecutorStats {
public:
/**
* Get the current value of ServiceExecutorStats for the given ServiceContext.
*
* Note that this value is intended for statistics and logging. It is unsynchronized and
* unsuitable for informing decisions in runtime.
*/
static ServiceExecutorStats get(ServiceContext* ctx) noexcept;
// The number of Clients who use the dedicated executors.
size_t usesDedicated = 0;
// The number of Clients who use the borrowed executors.
size_t usesBorrowed = 0;
// The number of Clients that are allowed to ignore maxConns and use reserved resources.
size_t limitExempt = 0;
};
} // namespace transport
ENABLE_BITMASK_OPERATORS(transport::ServiceExecutor::ScheduleFlags)
} // namespace mongo
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