mungedb-aggregate/lib/query/Runner.js

"use strict";

/**
 * This class is an implementation of the base class for runners used in MongoDB
 *
 * Note that a lot of stuff here is not used by our code yet.  Check the existing implementations
 * for what we currently use
 *
 **/
var klass = module.exports = function Runner(){

}, proto = klass.prototype;

klass.RunnerState = {
	// We successfully populated the out parameter.
	RUNNER_ADVANCED: "RUNNER_ADVANCED",

	// We're EOF.  We won't return any more results (edge case exception: capped+tailable).
	RUNNER_EOF: "RUNNER_EOF",

	// We were killed or had an error.
	RUNNER_DEAD: "RUNNER_DEAD",

	// getNext was asked for data it cannot provide, or the underlying PlanStage had an
	// unrecoverable error.
	// If the underlying PlanStage has any information on the error, it will be available in
	// the objOut parameter. Call WorkingSetCommon::toStatusString() to retrieve the error
	// details from the output BSON object.
	RUNNER_ERROR: "RUNNER_ERROR"
};

klass.YieldPolicy = {
	// Any call to getNext() may yield.  In particular, the runner may be killed during any
	// call to getNext().  If this occurs, getNext() will return RUNNER_DEAD.
	//
	// If you are enabling autoyield, you must register the Runner with ClientCursor via
	// ClientCursor::registerRunner and deregister via ClientCursor::deregisterRunnerwhen
	// done.  Registered runners are informed about DiskLoc deletions and Namespace
	// invalidations and other important events.
	//
	// Exception: This is not required if the Runner is cached inside of a ClientCursor.
	// This is only done if the Runner is cached and can be referred to by a cursor id.
	// This is not a popular thing to do.
	YIELD_AUTO: "YIELD_AUTO",

	// Owner must yield manually if yields are requested.  How to yield yourself:
	//
	// 0. Let's say you have Runner* runner.
	//
	// 1. Register your runner with ClientCursor.  Registered runners are informed about
	// DiskLoc deletions and Namespace invalidation and other important events.  Do this by
	// calling ClientCursor::registerRunner(runner).  This could be done once when you get
	// your runner, or per-yield.
	//
	// 2. Call runner->saveState() before you yield.
	//
	// 3. Call RunnerYieldPolicy::staticYield(runner->ns(), NULL) to yield.  Any state that
	// may change between yields must be checked by you.  (For example, DiskLocs may not be
	// valid across yielding, indices may be dropped, etc.)
	//
	// 4. Call runner->restoreState() before using the runner again.
	//
	// 5. Your runner's next call to getNext may return RUNNER_DEAD.
	//
	// 6. When you're done with your runner, deregister it from ClientCursor via
	// ClientCursor::deregister(runner).
	YIELD_MANUAL: "YIELD_MANUAL"
};


/**
 * Set the yielding policy of the underlying runner.  See the RunnerYieldPolicy enum above.
 *
 * @method setYieldPolicy
 * @param [policy]
 */
proto.setYieldPolicy = function setYieldPolicy(policy) {
	throw new Error("Not implemented");
};

/**
 * Get the next result from the query.
 *
 * If objOut is not NULL, only results that have a BSONObj are returned.  The BSONObj may
 * point to on-disk data (isOwned will be false) and must be copied by the caller before
 * yielding.
 *
 * If dlOut is not NULL, only results that have a valid DiskLoc are returned.
 *
 * If both objOut and dlOut are not NULL, only results with both a valid BSONObj and DiskLoc
 * will be returned.  The BSONObj is the object located at the DiskLoc provided.
 *
 * If the underlying query machinery produces a result that does not have the data requested
 * by the user, it will be silently dropped.
 *
 * If the caller is running a query, they probably only care about the object.
 * If the caller is an internal client, they may only care about DiskLocs (index scan), or
 * about object + DiskLocs (collection scan).
 *
 * Some notes on objOut and ownership:
 *
 * objOut may be an owned object in certain cases: invalidation of the underlying DiskLoc,
 * the object is created from covered index key data, the object is projected or otherwise
 * the result of a computation.
 *
 * objOut will also be owned when the underlying PlanStage has provided error details in the
 * event of a RUNNER_ERROR. Call WorkingSetCommon::toStatusString() to convert the object
 * to a loggable format.
 *
 * objOut will be unowned if it's the result of a fetch or a collection scan.
 *
 * @method getNext
 * @param [callback] {Function}
 */
proto.getNext = function getNext(callback) {
	throw new Error("Not implemented");
};


/**
 * Will the next call to getNext() return EOF?  It's useful to know if the runner is done
 * without having to take responsibility for a result.
 *
 * @method isEOF
 */
proto.isEOF = function isEOF(){
	throw new Error("Not implemented");
};

/**
 * Inform the runner about changes to DiskLoc(s) that occur while the runner is yielded.
 * The runner must take any actions required to continue operating correctly, including
 * broadcasting the invalidation request to the PlanStage tree being run.
 *
 * Called from CollectionCursorCache::invalidateDocument.
 *
 * See db/invalidation_type.h for InvalidationType.
 *
 * @method invalidate
 * @param [dl]
 * @param [type]
 */
proto.invalidate = function invalidate(dl, type) {
	throw new Error("Not implemented");
};

/**
 * Mark the Runner as no longer valid.  Can happen when a runner yields and the underlying
 * database is dropped/indexes removed/etc.  All future to calls to getNext return
 * RUNNER_DEAD. Every other call is a NOOP.
 *
 * The runner must guarantee as a postcondition that future calls to collection() will
 * return NULL.
 *
 * @method kill
 */
proto.kill = function kill() {
	throw new Error("Not implemented");
};

/**
 * Save any state required to yield.
 *
 * @method saveState
 */
proto.saveState = function saveState() {
	throw new Error("Not implemented");
};

/**
 * Restore saved state, possibly after a yield.  Return true if the runner is OK, false if
 * it was killed.
 *
 * @method restoreState
 */
proto.restoreState = function restoreState() {
	throw new Error("Not implemented");
};

/**
 * Return the NS that the query is running over.
 *
 * @method ns
 */
proto.ns = function ns() {
	throw new Error("Not implemented");
};

/**
 * Return the Collection that the query is running over.
 *
 * @method collection
 */
proto.collection = function collection() {
	throw new Error("Not implemented");
};

/**
 * Returns OK, allocating and filling "*explain" or "*planInfo" with a description of the
 * chosen plan, depending on which is non-NULL (one of the two should be NULL). Caller
 * takes onwership of either "*explain" and "*planInfo". Otherwise, returns false
 * a detailed error status.
 *
 * If "explain" is NULL, then this out-parameter is ignored. Similarly, if "staticInfo"
 * is NULL, then no static debug information is produced.
 *
 * @method getInfo
 * @param [explain]
 * @param [planInfo]
 */
proto.getInfo = function getInfo(explain, planInfo) {
	throw new Error("Not implemented");
};