SERVER-28173 create a component that sends requests in parallel to multiple hosts over ASIO

1 files changed, 283 insertions, 0 deletions

diff --git a/src/mongo/s/async_requests_sender.h b/src/mongo/s/async_requests_sender.h
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+/**
+ *    Copyright (C) 2017 MongoDB Inc.
+ *
+ *    This program is free software: you can redistribute it and/or  modify
+ *    it under the terms of the GNU Affero General Public License, version 3,
+ *    as published by the Free Software Foundation.
+ *
+ *    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
+ *    GNU Affero General Public License for more details.
+ *
+ *    You should have received a copy of the GNU Affero General Public License
+ *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *    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 GNU Affero General 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 <boost/optional.hpp>
+#include <vector>
+
+#include "mongo/base/disallow_copying.h"
+#include "mongo/base/status_with.h"
+#include "mongo/bson/bsonobj.h"
+#include "mongo/client/read_preference.h"
+#include "mongo/executor/remote_command_response.h"
+#include "mongo/executor/task_executor.h"
+#include "mongo/s/client/shard.h"
+#include "mongo/s/shard_id.h"
+#include "mongo/stdx/mutex.h"
+#include "mongo/util/concurrency/notification.h"
+#include "mongo/util/net/hostandport.h"
+#include "mongo/util/time_support.h"
+
+namespace mongo {
+
+/**
+ * The AsyncRequestsSender allows for sending requests to a set of remote shards in parallel and
+ * automatically retrying on retriable errors according to a RetryPolicy. It can also allow for
+ * retrieving partial results by ignoring shards that return errors.
+ *
+ * Work on remote nodes is accomplished by scheduling remote work in a TaskExecutor's event loop.
+ *
+ * Typical usage is:
+ *
+ * AsyncRequestsSender ars(txn, executor, db, requests, readPrefSetting);  // schedule the requests
+ * auto responses = ars.waitForResponses(txn);  // wait for responses; retries on retriable erors
+ *
+ * Additionally, you can interrupt() (if you want waitForResponses() to wait for responses for
+ * outstanding requests but stop scheduling retries) or kill() (if you want to cancel outstanding
+ * requests) the ARS from another thread.
+ *
+ * Does not throw exceptions.
+ */
+class AsyncRequestsSender {
+    MONGO_DISALLOW_COPYING(AsyncRequestsSender);
+
+public:
+    /**
+     * Defines a request to a remote shard that can be run by the ARS.
+     */
+    struct Request {
+        Request(ShardId shardId, BSONObj cmdObj);
+
+        // ShardId of the shard to which the command will be sent.
+        const ShardId shardId;
+
+        // The command object to send to the remote host.
+        const BSONObj cmdObj;
+    };
+
+    /**
+     * Defines a response for a request to a remote shard.
+     */
+    struct Response {
+        // Constructor for a response that was successfully received.
+        Response(executor::RemoteCommandResponse response, HostAndPort hp);
+
+        // Constructor that specifies the reason the response was not successfully received.
+        Response(Status status);
+
+        // The response or error from the remote.
+        StatusWith<executor::RemoteCommandResponse> swResponse;
+
+        // The exact host on which the remote command was run. Is unset if swResponse has a non-OK
+        // status.
+        boost::optional<HostAndPort> shardHostAndPort;
+    };
+
+    /**
+     * Constructs a new AsyncRequestsSender. The TaskExecutor* must remain valid for the lifetime of
+     * the ARS.
+     */
+    AsyncRequestsSender(OperationContext* txn,
+                        executor::TaskExecutor* executor,
+                        std::string db,
+                        const std::vector<AsyncRequestsSender::Request>& requests,
+                        const ReadPreferenceSetting& readPreference,
+                        bool allowPartialResults = false);
+
+    ~AsyncRequestsSender();
+
+    /**
+     * Returns a vector containing the responses or errors for each remote in the same order as the
+     * input vector that was passed in the constructor.
+     *
+     * If we were killed, returns immediately.
+     * If we were interrupted, returns when any outstanding requests have completed.
+     * Otherwise, returns when each remote has received a response or error.
+     */
+    std::vector<Response> waitForResponses(OperationContext* txn);
+
+    /**
+     * Stops the ARS from retrying requests. Causes waitForResponses() to wait until any outstanding
+     * requests have received a response or error.
+     *
+     * Use this if you no longer care about getting success responses, but need to do cleanup based
+     * on responses for requests that have already been dispatched.
+     */
+    void interrupt();
+
+    /**
+     * Cancels all outstanding requests and makes waitForResponses() return immediately.
+     *
+     * Use this if you no longer care about getting success responses, and don't need to process
+     * responses for outstanding requests.
+     */
+    void kill();
+
+private:
+    /**
+     * Returns true if each remote has received a response or error. (If kill() has been called,
+     * the error is the error assigned by the TaskExecutor when a callback is canceled).
+     */
+    bool _done();
+
+    /**
+     * Executes the logic of _done().
+     */
+    bool _done_inlock();
+
+    /**
+     * Replaces _notification with a new notification.
+     *
+     * If _stopRetrying is false, for each remote that does not have a response or outstanding
+     * request, schedules work to send the command to the remote.
+     *
+     * Invalid to call if there is an existing Notification and it has not yet been signaled.
+     */
+    void _scheduleRequestsIfNeeded(OperationContext* txn);
+
+    /**
+     * Helper to schedule a command to a remote.
+     *
+     * The 'remoteIndex' gives the position of the remote node from which we are retrieving the
+     * batch in '_remotes'.
+     *
+     * Returns success if the command to retrieve the next batch was scheduled successfully.
+     */
+    Status _scheduleRequest_inlock(OperationContext* txn, size_t remoteIndex);
+
+    /**
+     * The callback for a remote command.
+     *
+     * 'remoteIndex' is the position of the relevant remote node in '_remotes', and therefore
+     * indicates which node the response came from and where the response should be buffered.
+     *
+     * On a retriable error, unless _stopRetrying is true, signals the notification so that the
+     * request can be immediately retried.
+     *
+     * On a non-retriable error, if allowPartialResults is false, sets _stopRetrying to true.
+     */
+    void _handleResponse(const executor::TaskExecutor::RemoteCommandCallbackArgs& cbData,
+                         OperationContext* txn,
+                         size_t remoteIndex);
+
+    /**
+     * If the existing notification has not yet been signaled, signals it and marks it as signaled.
+     */
+    void _signalCurrentNotification_inlock();
+
+    /**
+     * Wrapper around signalCurrentNotification_inlock(); only signals the notification if _done()
+     * is true.
+     */
+    void _signalCurrentNotificationIfDone_inlock();
+
+    /**
+     * We instantiate one of these per remote host.
+     */
+    struct RemoteData {
+        /**
+         * Creates a new uninitialized remote state with a command to send.
+         */
+        RemoteData(ShardId shardId, BSONObj cmdObj);
+
+        /**
+         * Returns the resolved host and port on which the remote command was or will be run.
+         */
+        const HostAndPort& getTargetHost() const;
+
+        /**
+         * Given a read preference, selects a host on which the command should be run.
+         */
+        Status resolveShardIdToHostAndPort(const ReadPreferenceSetting& readPref);
+
+        /**
+         * Returns the Shard object associated with this remote.
+         */
+        std::shared_ptr<Shard> getShard();
+
+        // ShardId of the shard to which the command will be sent.
+        const ShardId shardId;
+
+        // The command object to send to the remote host.
+        BSONObj cmdObj;
+
+        // The response or error from the remote. Is unset until a response or error has been
+        // received.
+        boost::optional<StatusWith<executor::RemoteCommandResponse>> swResponse;
+
+        // The exact host on which the remote command was run. Is unset until a request has been
+        // sent.
+        boost::optional<HostAndPort> shardHostAndPort;
+
+        // The number of times we've retried sending the command to this remote.
+        int retryCount = 0;
+
+        // The callback handle to an outstanding request for this remote.
+        executor::TaskExecutor::CallbackHandle cbHandle;
+    };
+
+    /**
+     * Used internally to determine if the ARS should attempt to retry any requests. Is set to true
+     * when:
+     * - interrupt() or kill() is called
+     * - allowPartialResults is false and some remote has a non-retriable error (or exhausts its
+     *  retries for a retriable error).
+     */
+    bool _stopRetrying = false;
+
+    // Not owned here.
+    executor::TaskExecutor* _executor;
+
+    // The metadata obj to pass along with the command remote. Used to indicate that the command is
+    // ok to run on secondaries.
+    BSONObj _metadataObj;
+
+    // The database against which the commands are run.
+    const std::string _db;
+
+    // The readPreference to use for all requests.
+    ReadPreferenceSetting _readPreference;
+
+    // If set to true, allows for skipping over hosts that have non-retriable errors or exhaust
+    // their retries.
+    bool _allowPartialResults = false;
+
+    // Must be acquired before accessing any data members.
+    // Must also be held when calling any of the '_inlock()' helper functions.
+    stdx::mutex _mutex;
+
+    // Data tracking the state of our communication with each of the remote nodes.
+    std::vector<RemoteData> _remotes;
+
+    // A notification that gets signaled when a remote has a retriable error or the last outstanding
+    // response is received.
+    boost::optional<Notification<void>> _notification;
+};
+
+}  // namespace mongo