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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 "mongo/base/status.h"
#include "mongo/util/functional.h"
namespace mongo {
/**
* Provides the minimal api for a simple out of line executor that can run non-cancellable
* callbacks.
*
* The contract for scheduling work on an executor is that it never blocks the caller. It doesn't
* necessarily need to offer forward progress guarantees, but actual calls to schedule() should not
* deadlock.
*
* If you manage the lifetime of your executor using a shared_ptr, you can begin a chain of
* execution like this:
* ExecutorFuture(myExec)
* .then([] { return doThing1(); })
* .then([] { return doThing2(); })
* ...
*/
class OutOfLineExecutor {
public:
using Task = unique_function<void(Status)>;
public:
/**
* Delegates invocation of the Task to this executor
*
* Execution of the Task can happen in one of three contexts:
* * By default, on an execution context maintained by the OutOfLineExecutor (i.e. a thread).
* * During shutdown, on the execution context of shutdown/join/dtor for the OutOfLineExecutor.
* * Post-shutdown, on the execution context of the calling code.
*
* The Task will be passed a Status schedStatus that is either:
* * schedStatus.isOK() if the function is run in an out-of-line context
* * isCancelationError(schedStatus.code()) if the function is run in an inline context
*
* All of this is to say: CHECK YOUR STATUS.
*/
virtual void schedule(Task func) = 0;
virtual ~OutOfLineExecutor() = default;
};
using ExecutorPtr = std::shared_ptr<OutOfLineExecutor>;
} // namespace mongo
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