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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.
*/
#include "mongo/platform/basic.h"
#include "mongo/db/query/find_common.h"
#include "mongo/db/session_catalog_mongod.h"
#include "mongo/db/transaction_participant.h"
#include "mongo/s/query/blocking_results_merger.h"
namespace mongo {
BlockingResultsMerger::BlockingResultsMerger(OperationContext* opCtx,
AsyncResultsMergerParams&& armParams,
executor::TaskExecutor* executor,
std::unique_ptr<ResourceYielder> resourceYielder)
: _tailableMode(armParams.getTailableMode().value_or(TailableModeEnum::kNormal)),
_executor(executor),
_arm(opCtx, executor, std::move(armParams)),
_resourceYielder(std::move(resourceYielder)) {}
StatusWith<stdx::cv_status> BlockingResultsMerger::doWaiting(
OperationContext* opCtx, const std::function<StatusWith<stdx::cv_status>()>& waitFn) noexcept {
if (_resourceYielder) {
try {
// The BRM interface returns Statuses. Be sure we respect that here.
_resourceYielder->yield(opCtx);
} catch (const DBException& e) {
return e.toStatus();
}
}
boost::optional<StatusWith<stdx::cv_status>> result;
try {
// This shouldn't throw, but we cannot enforce that.
result = waitFn();
} catch (const DBException&) {
MONGO_UNREACHABLE;
}
if (_resourceYielder) {
try {
_resourceYielder->unyield(opCtx);
} catch (const DBException& e) {
return e.toStatus();
}
}
return *result;
}
StatusWith<ClusterQueryResult> BlockingResultsMerger::awaitNextWithTimeout(
OperationContext* opCtx, RouterExecStage::ExecContext execCtx) {
invariant(_tailableMode == TailableModeEnum::kTailableAndAwaitData);
// If we are in kInitialFind or kGetMoreWithAtLeastOneResultInBatch context and the ARM is not
// ready, we don't block. Fall straight through to the return statement.
while (!_arm.ready() && execCtx == RouterExecStage::ExecContext::kGetMoreNoResultsYet) {
auto nextEventStatus = getNextEvent();
if (!nextEventStatus.isOK()) {
return nextEventStatus.getStatus();
}
auto event = nextEventStatus.getValue();
const auto waitStatus = doWaiting(opCtx, [this, opCtx, &event]() {
return _executor->waitForEvent(
opCtx, event, awaitDataState(opCtx).waitForInsertsDeadline);
});
if (!waitStatus.isOK()) {
return waitStatus.getStatus();
}
// Swallow timeout errors for tailable awaitData cursors, stash the event that we were
// waiting on, and return EOF.
if (waitStatus == stdx::cv_status::timeout) {
_leftoverEventFromLastTimeout = std::move(event);
return ClusterQueryResult{};
}
}
// We reach this point either if the ARM is ready, or if the ARM is !ready and we are in
// kInitialFind or kGetMoreWithAtLeastOneResultInBatch ExecContext. In the latter case, we
// return EOF immediately rather than blocking for further results.
return _arm.ready() ? _arm.nextReady() : ClusterQueryResult{};
}
StatusWith<ClusterQueryResult> BlockingResultsMerger::blockUntilNext(OperationContext* opCtx) {
while (!_arm.ready()) {
auto nextEventStatus = _arm.nextEvent();
if (!nextEventStatus.isOK()) {
return nextEventStatus.getStatus();
}
auto event = nextEventStatus.getValue();
// Block until there are further results to return.
auto status = doWaiting(
opCtx, [this, opCtx, &event]() { return _executor->waitForEvent(opCtx, event); });
if (!status.isOK()) {
return status.getStatus();
}
// We have not provided a deadline, so if the wait returns without interruption, we do not
// expect to have timed out.
invariant(status.getValue() == stdx::cv_status::no_timeout);
}
return _arm.nextReady();
}
StatusWith<ClusterQueryResult> BlockingResultsMerger::next(OperationContext* opCtx,
RouterExecStage::ExecContext execCtx) {
// Non-tailable and tailable non-awaitData cursors always block until ready(). AwaitData
// cursors wait for ready() only until a specified time limit is exceeded.
return (_tailableMode == TailableModeEnum::kTailableAndAwaitData
? awaitNextWithTimeout(opCtx, execCtx)
: blockUntilNext(opCtx));
}
StatusWith<executor::TaskExecutor::EventHandle> BlockingResultsMerger::getNextEvent() {
// If we abandoned a previous event due to a mongoS-side timeout, wait for it first.
if (_leftoverEventFromLastTimeout) {
invariant(_tailableMode == TailableModeEnum::kTailableAndAwaitData);
// If we have an outstanding event from last time, then we might have to manually schedule
// some getMores for the cursors. If a remote response came back while we were between
// getMores (from the user to mongos), the response may have been an empty batch, and the
// ARM would not be able to ask for the next batch immediately since it is not attached to
// an OperationContext. Now that we have a valid OperationContext, we schedule the getMores
// ourselves.
Status getMoreStatus = _arm.scheduleGetMores();
if (!getMoreStatus.isOK()) {
return getMoreStatus;
}
// Return the leftover event and clear '_leftoverEventFromLastTimeout'.
auto event = _leftoverEventFromLastTimeout;
_leftoverEventFromLastTimeout = executor::TaskExecutor::EventHandle();
return event;
}
return _arm.nextEvent();
}
void BlockingResultsMerger::kill(OperationContext* opCtx) {
auto killEvent = _arm.kill(opCtx);
if (!killEvent) {
// We are shutting down.
return;
}
_executor->waitForEvent(killEvent);
}
} // namespace mongo
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