From: Joao Eduardo Luis Date: Wed, 23 May 2012 01:32:04 +0000 (-0700) Subject: mon: add doxygen-format comments to the Elector class. X-Git-Tag: v0.48argonaut~151^2~3 X-Git-Url: http://git-server-git.apps.pok.os.sepia.ceph.com/?a=commitdiff_plain;h=8c95e8bc38acb3c25199f5365635753f92ee9487;p=ceph.git mon: add doxygen-format comments to the Elector class. Signed-off-by: Joao Eduardo Luis --- diff --git a/src/mon/Elector.h b/src/mon/Elector.h index c4e0f5cad6b7..3f3b508f45b6 100644 --- a/src/mon/Elector.h +++ b/src/mon/Elector.h @@ -28,31 +28,141 @@ using namespace std; class Monitor; - +/** + * This class is responsible for maintaining the local state when electing + * a new Leader. We may win or we may lose. If we win, it means we became the + * Leader; if we lose, it means we are a Peon. + */ class Elector { + /** + * @defgroup Elector_h_class Elector + * @{ + */ private: + /** + * The Monitor instance associated with this class. + */ Monitor *mon; + /** + * Event callback responsible for dealing with an expired election once a + * timer runs out and fires up. + */ Context *expire_event; + /** + * Resets the expire_event timer, by cancelling any existing one and + * scheduling a new one. + * + * @remarks This function assumes as a default firing value the duration of + * the monitor's lease interval, and adds to it the value specified + * in @plus + * + * @post expire_event is set + * + * @param plus The amount of time to be added to the default firing value. + */ void reset_timer(double plus=0.0); + /** + * Cancel the expire_event timer, if it is defined. + * + * @post expire_event is not set + */ void cancel_timer(); - epoch_t epoch; // latest epoch we've seen. odd == election, even == stable, + /** + * Latest epoch we've seen. + * + * @remarks if its value is odd, we're electing; if it's even, then we're + * stable. + */ + epoch_t epoch; + /** + * Indicates if we are participating in the quorum. + * + * @remarks By default, we are created as participating. We may stop + * participating if the Monitor explicitely calls + * Elector::stop_participating though. If that happens, it will + * have to call Elector::start_participating for us to resume + * participating in the quorum. + */ bool participating; // electing me + /** + * @defgroup Elector_h_electing_me_vars We are being elected + * @{ + */ + /** + * Indicates if we are the ones being elected. + * + * We always attempt to be the one being elected if we are the ones starting + * the election. If we are not the ones that started it, we will only attempt + * to be elected if we think we might have a chance (i.e., the other guy's + * rank is lower than ours). + */ bool electing_me; + /** + * Holds the time at which we started the election. + */ utime_t start_stamp; + /** + * Set containing all those that acked our proposal to become the Leader. + * + * If we are acked by everyone in the MonMap, we will declare victory. + */ set acked_me; + /** + * @} + */ + /** + * @defgroup Elector_h_electing_them_vars We are electing another guy + * @{ + */ + /** + * Indicates who we have acked + */ + int leader_acked; + /** + * Indicates when we have acked him + */ + utime_t ack_stamp; + /** + * @} + */ + + /** + * Update our epoch. + * + * If we come across a higher epoch, we simply update ours, also making + * sure we are no longer being elected (even though we could have been, + * we no longer are since we no longer are on that old epoch). + * + * @pre Our epoch is lower than @p e + * @post Our epoch equals @p e + * + * @param e Epoch to which we will update our epoch + */ + void bump_epoch(epoch_t e=0); - // electing them - int leader_acked; // who i've acked - utime_t ack_stamp; // and when - - void bump_epoch(epoch_t e=0); // i just saw a larger epoch - + /** + * @defgroup Elector_h_callbacks Callbacks + * @{ + */ + /** + * This class is used as the callback when the expire_event timer fires up. + * + * If the expire_event is fired, then it means that we had an election going, + * either started by us or by some other participant, but it took too long, + * thus expiring. + * + * When the election expires, we will check if we were the ones who won, and + * if so we will declare victory. If that is not the case, then we assume + * that the one we defered to didn't declare victory quickly enough (in fact, + * as far as we know, we may even be dead); so, just propose ourselves as the + * Leader. + */ class C_ElectionExpire : public Context { Elector *elector; public: @@ -61,17 +171,155 @@ class Elector { elector->expire(); } }; + /** + * @} + */ - void start(); // start an electing me + /** + * Start new elections by proposing ourselves as the new Leader. + * + * Basically, send propose messages to all the monitors in the MonMap and + * then reset the expire_event timer so we can limit the amount of time we + * will be going at it. + * + * @pre participating is true + * @post epoch is an odd value + * @post electing_me is true + * @post we sent propose messages to all the monitors in the MonMap + * @post we reset the expire_event timer + */ + void start(); + /** + * Defer the current election to some other monitor. + * + * This means that we will ack some other monitor and drop out from the run + * to become the Leader. We will only defer an election if the monitor we + * are deferring to outranks us. + * + * @pre @p who outranks us (i.e., who < our rank) + * @pre @p who outranks any other monitor we have deferred to in the past + * @post electing_me is false + * @post leader_acked equals @p who + * @post we sent an ack message to @p who + * @post we reset the expire_event timer + * + * @param who Some other monitor's numeric identifier. + */ void defer(int who); - void expire(); // timer goes off + /** + * The election has taken too long and has expired. + * + * This will happen when no one declared victory or started a new election + * during the time span allowed by the expire_event timer. + * + * When the election expires, we will check if we were the ones who won, and + * if so we will declare victory. If that is not the case, then we assume + * that the one we defered to didn't declare victory quickly enough (in fact, + * as far as we know, we may even be dead); so, just propose ourselves as the + * Leader. + */ + void expire(); + /** + * Declare Victory. + * + * We won. Or at least we believe we won, but for all intentions and purposes + * that does not matter. What matters is that we Won. + * + * That said, we must now bump our epoch to reflect that the election is over + * and then we must let everybody in the quorum know we are their brand new + * Leader. And we will also cancel our expire_event timer. + * + * Actually, the quorum will be now defined as the group of monitors that + * acked us during the election process. + * + * @pre Election is on-going + * @pre electing_me is true + * @post electing_me is false + * @post epoch is bumped up into an even value + * @post Election is not on-going + * @post We have a quorum, composed of the monitors that acked us + * @post We sent a message of type OP_VICTORY to each quorum member. + */ void victory(); - + + /** + * Handle a message from some other node proposing himself to become him + * the Leader. + * + * If the message appears to be old (i.e., its epoch is lower than our epoch), + * then we may take one of two actions: + * + * @li Ignore it because it's nothing more than an old proposal + * @li Start new elections if we verify that it was sent by a monitor from + * outside the quorum; given its old state, it's fair to assume he just + * started, so we should start new elections so he may rejoin + * + * If we did not ignore the received message, then we know that this message + * was sent by some other node proposing himself to become the Leader. So, we + * will take one of the following actions: + * + * @li Ignore him because we already acked another node with higher rank + * @li Ignore him and start a new election because we outrank him + * @li Defer to him because he outranks us and the node we previously + * acked, if any + * + * + * @invariant The received message is an operation of type OP_PROPOSE + * + * @param m A message sent by another participant in the quorum. + */ void handle_propose(class MMonElection *m); + /** + * Handle a message from some other participant Acking us as the Leader. + * + * When we receive such a message, one of three thing may be happening: + * @li We received a message with a newer epoch, which means we must have + * somehow lost track of what was going on (maybe we rebooted), thus we + * will start a new election + * @li We consider ourselves in the run for the Leader (i.e., @p electing_me + * is true), and we are actually being Acked by someone; thus simply add + * the one acking us to the @p acked_me set. If we do now have acks from + * all the participants, then we can declare victory + * @li We already deferred the election to somebody else, so we will just + * ignore this message + * + * @pre Election is on-going + * @post Election is on-going if we deferred to somebody else + * @post Election is on-going if we are still waiting for further Acks + * @post Election is not on-going if we are victorious + * @post Election is not on-going if we must start a new one + * + * @param m A message with an operation type of OP_ACK + */ void handle_ack(class MMonElection *m); + /** + * Handle a message from some other participant declaring Victory. + * + * We just got a message from someone declaring themselves Victorious, thus + * the new Leader. + * + * However, if the message's epoch happens to be different from our epoch+1, + * then it means we lost track of something and we must start a new election. + * + * If that is not the case, then we will simply update our epoch to the one + * in the message, cancel our @p expire_event timer and inform our Monitor + * that we lost the election and provide it with the new quorum. + * + * @pre Election in on-going + * @post Election is not on-going + * @post Updated @p epoch + * @post We have a new quorum if we lost the election + * + * @param m A message with an operation type of OP_VICTORY + */ void handle_victory(class MMonElection *m); - public: + public: + /** + * Create an Elector class + * + * @param m A Monitor instance + */ Elector(Monitor *m) : mon(m), expire_event(0), epoch(0), @@ -79,20 +327,74 @@ class Elector { electing_me(false), leader_acked(-1) { } + /** + * Initiate the Elector class. + * + * Basically, we will simply read whatever epoch value we have in our stable + * storage, or consider it to be 1 if none is read. + * + * @post @p epoch is set to 1 or higher. + */ void init(); + /** + * Inform this class it is supposed to shutdown. + * + * We will simply cancel the @p expire_event if any exists. + * + * @post @p expire_event is cancelled + */ void shutdown(); + /** + * Obtain our epoch + * + * @returns Our current epoch number + */ epoch_t get_epoch() { return epoch; } + /** + * Handle received messages. + * + * We will ignore all messages that are not of type @p MSG_MON_ELECTION + * (i.e., messages whose interface is not of type @p MMonElection). All of + * those that are will then be dispatched to their operation-specific + * functions. + * + * @param m A received message + */ void dispatch(Message *m); + /** + * Call an election. + * + * This function simply calls Elector::start. + */ void call_election() { start(); } + /** + * Stop participating in subsequent Elections. + * + * @post @p participating is false + */ void stop_participating() { participating = false; } + /** + * Start participating in Elections. + * + * If we are already participating (i.e., @p participating is true), then + * calling this function is moot. + * + * However, if we are not participating (i.e., @p participating is false), + * then we will start participating by setting @p participating to true and + * we will call for an Election. + * + * @post @p participating is true + */ void start_participating(); + /** + * @} + */ }; - #endif