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MXS-1840 Compile all routers as C++

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Minimal changes, only what is needed in order to make it compile.
This commit is contained in:
Johan Wikman
2018-05-03 15:53:17 +03:00
parent 10b2b4ac37
commit 1f6cc6db8a
39 changed files with 476 additions and 427 deletions
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server/modules/routing/readconnroute/readconnroute.cc Normal file
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/*
* Copyright (c) 2016 MariaDB Corporation Ab
*
* Use of this software is governed by the Business Source License included
* in the LICENSE.TXT file and at www.mariadb.com/bsl11.
*
* Change Date: 2020-01-01
*
* On the date above, in accordance with the Business Source License, use
* of this software will be governed by version 2 or later of the General
* Public License.
*/
/**
* @file readconnroute.c - Read Connection Load Balancing Query Router
*
* This is the implementation of a simple query router that balances
* read connections. It assumes the service is configured with a set
* of slaves and that the application clients already split read and write
* queries. It offers a service to balance the client read connections
* over this set of slave servers. It does this once only, at the time
* the connection is made. It chooses the server that currently has the least
* number of connections by keeping a count for each server of how
* many connections the query router has made to the server.
*
* When two servers have the same number of current connections the one with
* the least number of connections since startup will be used.
*
* The router may also have options associated to it that will limit the
* choice of backend server. Currently two options are supported, the "master"
* option will cause the router to only connect to servers marked as masters
* and the "slave" option will limit connections to routers that are marked
* as slaves. If neither option is specified the router will connect to either
* masters or slaves.
*
* @verbatim
* Revision History
*
* Date Who Description
* 14/06/2013 Mark Riddoch Initial implementation
* 25/06/2013 Mark Riddoch Addition of checks for current server state
* 26/06/2013 Mark Riddoch Use server with least connections since
* startup if the number of current
* connections is the same for two servers
* Addition of master and slave options
* 27/06/2013 Vilho Raatikka Added skygw_log_write command as an example
* and necessary headers.
* 17/07/2013 Massimiliano Pinto Added clientReply routine:
* called by backend server to send data to client
* Included maxscale/protocol/mysql.h
* with macros and MySQL commands with MYSQL_ prefix
* avoiding any conflict with the standard ones
* in mysql.h
* 22/07/2013 Mark Riddoch Addition of joined router option for Galera
* clusters
* 31/07/2013 Massimiliano Pinto Added a check for candidate server, if NULL return
* 12/08/2013 Mark Riddoch Log unsupported router options
* 04/09/2013 Massimiliano Pinto Added client NULL check in clientReply
* 22/10/2013 Massimiliano Pinto errorReply called from backend, for client error reply
* or take different actions such as open a new backend connection
* 20/02/2014 Massimiliano Pinto If router_options=slave, route traffic to master if no slaves available
* 06/03/2014 Massimiliano Pinto Server connection counter is now updated in closeSession
* 24/06/2014 Massimiliano Pinto New rules for selecting the Master server
* 27/06/2014 Mark Riddoch Addition of server weighting
* 11/06/2015 Martin Brampton Remove decrement n_current (moved to dcb.c)
* 09/09/2015 Martin Brampton Modify error handler
* 25/09/2015 Martin Brampton Block callback processing when no router session in the DCB
* 09/11/2015 Martin Brampton Modified routeQuery - must free "queue" regardless of outcome
*
* @endverbatim
*/
#include "readconnection.h"
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <signal.h>
#include <maxscale/alloc.h>
#include <maxscale/server.h>
#include <maxscale/router.h>
#include <maxscale/atomic.h>
#include <maxscale/spinlock.h>
#include <maxscale/dcb.h>
#include <maxscale/modinfo.h>
#include <maxscale/log_manager.h>
#include <maxscale/protocol/mysql.h>
#include <maxscale/modutil.h>
/* The router entry points */
static MXS_ROUTER *createInstance(SERVICE *service, char **options);
static MXS_ROUTER_SESSION *newSession(MXS_ROUTER *instance, MXS_SESSION *session);
static void closeSession(MXS_ROUTER *instance, MXS_ROUTER_SESSION *router_session);
static void freeSession(MXS_ROUTER *instance, MXS_ROUTER_SESSION *router_session);
static int routeQuery(MXS_ROUTER *instance, MXS_ROUTER_SESSION *router_session, GWBUF *queue);
static void diagnostics(MXS_ROUTER *instance, DCB *dcb);
static json_t* diagnostics_json(const MXS_ROUTER *instance);
static void clientReply(MXS_ROUTER *instance, MXS_ROUTER_SESSION *router_session, GWBUF *queue,
DCB *backend_dcb);
static void handleError(MXS_ROUTER *instance, MXS_ROUTER_SESSION *router_session, GWBUF *errbuf,
DCB *problem_dcb, mxs_error_action_t action, bool *succp);
static uint64_t getCapabilities(MXS_ROUTER* instance);
static bool rses_begin_locked_router_action(ROUTER_CLIENT_SES* rses);
static void rses_end_locked_router_action(ROUTER_CLIENT_SES* rses);
static SERVER_REF *get_root_master(SERVER_REF *servers);
/**
* The module entry point routine. It is this routine that
* must populate the structure that is referred to as the
* "module object", this is a structure with the set of
* external entry points for this module.
*
* @return The module object
*/
extern "C" MXS_MODULE* MXS_CREATE_MODULE()
{
MXS_NOTICE("Initialise readconnroute router module.");
static MXS_ROUTER_OBJECT MyObject =
{
createInstance,
newSession,
closeSession,
freeSession,
routeQuery,
diagnostics,
diagnostics_json,
clientReply,
handleError,
getCapabilities,
NULL
};
static MXS_MODULE info =
{
MXS_MODULE_API_ROUTER,
MXS_MODULE_GA,
MXS_ROUTER_VERSION,
"A connection based router to load balance based on connections",
"V1.1.0",
MXS_NO_MODULE_CAPABILITIES,
&MyObject,
NULL, /* Process init. */
NULL, /* Process finish. */
NULL, /* Thread init. */
NULL, /* Thread finish. */
{
{MXS_END_MODULE_PARAMS}
}
};
return &info;
}
static inline void free_readconn_instance(ROUTER_INSTANCE *router)
{
if (router)
{
MXS_FREE(router);
}
}
/**
* Create an instance of the router for a particular service
* within the gateway.
*
* @param service The service this router is being create for
* @param options An array of options for this query router
*
* @return The instance data for this new instance
*/
static MXS_ROUTER *
createInstance(SERVICE *service, char **options)
{
ROUTER_INSTANCE *inst;
SERVER_REF *sref;
int i, n;
if ((inst = static_cast<ROUTER_INSTANCE*>(MXS_CALLOC(1, sizeof(ROUTER_INSTANCE)))) == NULL)
{
return NULL;
}
inst->service = service;
spinlock_init(&inst->lock);
/*
* Process the options
*/
bool error = false;
inst->bitmask = 0;
inst->bitvalue = 0;
if (options)
{
for (i = 0; options[i]; i++)
{
if (!strcasecmp(options[i], "master"))
{
inst->bitmask |= (SERVER_MASTER | SERVER_SLAVE);
inst->bitvalue |= SERVER_MASTER;
}
else if (!strcasecmp(options[i], "slave"))
{
inst->bitmask |= (SERVER_MASTER | SERVER_SLAVE);
inst->bitvalue |= SERVER_SLAVE;
}
else if (!strcasecmp(options[i], "running"))
{
inst->bitmask |= (SERVER_RUNNING);
inst->bitvalue |= SERVER_RUNNING;
}
else if (!strcasecmp(options[i], "synced"))
{
inst->bitmask |= (SERVER_JOINED);
inst->bitvalue |= SERVER_JOINED;
}
else if (!strcasecmp(options[i], "ndb"))
{
inst->bitmask |= (SERVER_NDB);
inst->bitvalue |= SERVER_NDB;
}
else
{
MXS_WARNING("Unsupported router "
"option \'%s\' for readconnroute. "
"Expected router options are "
"[slave|master|synced|ndb|running]",
options[i]);
error = true;
}
}
}
if (error)
{
free_readconn_instance(inst);
return NULL;
}
if (inst->bitmask == 0 && inst->bitvalue == 0)
{
/** No parameters given, use RUNNING as a valid server */
inst->bitmask |= (SERVER_RUNNING);
inst->bitvalue |= SERVER_RUNNING;
}
/*
* We have completed the creation of the instance data, so now
* insert this router instance into the linked list of routers
* that have been created with this module.
*/
return (MXS_ROUTER *) inst;
}
/**
* Associate a new session with this instance of the router.
*
* @param instance The router instance data
* @param session The session itself
* @return Session specific data for this session
*/
static MXS_ROUTER_SESSION *
newSession(MXS_ROUTER *instance, MXS_SESSION *session)
{
ROUTER_INSTANCE *inst = (ROUTER_INSTANCE *) instance;
ROUTER_CLIENT_SES *client_rses;
SERVER_REF *candidate = NULL;
int i;
SERVER_REF *master_host = NULL;
MXS_DEBUG("%lu [newSession] new router session with session "
"%p, and inst %p.",
pthread_self(),
session,
inst);
client_rses = (ROUTER_CLIENT_SES *) MXS_CALLOC(1, sizeof(ROUTER_CLIENT_SES));
if (client_rses == NULL)
{
return NULL;
}
#if defined(SS_DEBUG)
client_rses->rses_chk_top = CHK_NUM_ROUTER_SES;
client_rses->rses_chk_tail = CHK_NUM_ROUTER_SES;
#endif
client_rses->client_dcb = session->client_dcb;
/**
* Find the Master host from available servers
*/
master_host = get_root_master(inst->service->dbref);
/**
* Find a backend server to connect to. This is the extent of the
* load balancing algorithm we need to implement for this simple
* connection router.
*/
/*
* Loop over all the servers and find any that have fewer connections
* than the candidate server.
*
* If a server has less connections than the current candidate we mark this
* as the new candidate to connect to.
*
* If a server has the same number of connections currently as the candidate
* and has had less connections over time than the candidate it will also
* become the new candidate. This has the effect of spreading the
* connections over different servers during periods of very low load.
*/
for (SERVER_REF *ref = inst->service->dbref; ref; ref = ref->next)
{
if (!SERVER_REF_IS_ACTIVE(ref) || SERVER_IN_MAINT(ref->server))
{
continue;
}
else
{
MXS_DEBUG("%lu [newSession] Examine server in port %d with "
"%d connections. Status is %s, "
"inst->bitvalue is %d",
pthread_self(),
ref->server->port,
ref->connections,
STRSRVSTATUS(ref->server),
inst->bitmask);
}
/* Check server status bits against bitvalue from router_options */
if (ref && SERVER_IS_RUNNING(ref->server) &&
(ref->server->status & inst->bitmask & inst->bitvalue))
{
if (master_host)
{
if (ref == master_host && (inst->bitvalue & (SERVER_SLAVE | SERVER_MASTER)) == SERVER_SLAVE)
{
/* Skip root master here, as it could also be slave of an external server that
* is not in the configuration. Intermediate masters (Relay Servers) are also
* slave and will be selected as Slave(s)
*/
continue;
}
if (ref == master_host && (inst->bitvalue & SERVER_MASTER))
{
/* If option is "master" return only the root Master as there could be
* intermediate masters (Relay Servers) and they must not be selected.
*/
candidate = master_host;
break;
}
}
else if (inst->bitvalue == SERVER_MASTER)
{
/* Master_host is NULL, no master server. If requested router_option is 'master'
* candidate will be NULL.
*/
candidate = NULL;
break;
}
/* If no candidate set, set first running server as our initial candidate server */
if (candidate == NULL)
{
candidate = ref;
}
else if (ref->weight == 0 || candidate->weight == 0)
{
candidate = ref->weight ? ref : candidate;
}
else if (((ref->connections + 1) * 1000) / ref->weight <
((candidate->connections + 1) * 1000) / candidate->weight)
{
/* This running server has fewer connections, set it as a new candidate */
candidate = ref;
}
else if (((ref->connections + 1) * 1000) / ref->weight ==
((candidate->connections + 1) * 1000) / candidate->weight &&
ref->server->stats.n_connections < candidate->server->stats.n_connections)
{
/* This running server has the same number of connections currently as the candidate
but has had fewer connections over time than candidate, set this server to
candidate*/
candidate = ref;
}
}
}
/* If we haven't found a proper candidate yet but a master server is available, we'll pick that
* with the assumption that it is "better" than a slave.
*/
if (!candidate)
{
if (master_host)
{
candidate = master_host;
}
else
{
MXS_ERROR("Failed to create new routing session. Couldn't find eligible"
" candidate server. Freeing allocated resources.");
MXS_FREE(client_rses);
return NULL;
}
}
/*
* We now have the server with the least connections.
* Bump the connection count for this server
*/
client_rses->backend = candidate;
/** Open the backend connection */
client_rses->backend_dcb = dcb_connect(candidate->server, session,
candidate->server->protocol);
if (client_rses->backend_dcb == NULL)
{
/** The failure is reported in dcb_connect() */
MXS_FREE(client_rses);
return NULL;
}
atomic_add(&candidate->connections, 1);
inst->stats.n_sessions++;
CHK_CLIENT_RSES(client_rses);
MXS_INFO("New session for server %s. Connections : %d",
candidate->server->name, candidate->connections);
return reinterpret_cast<MXS_ROUTER_SESSION*>(client_rses);
}
/**
* @node Unlink from backend server, unlink from router's connection list,
* and free memory of a router client session.
*
* Parameters:
* @param router - <usage>
* <description>
*
* @param router_cli_ses - <usage>
* <description>
*
* @return void
*
*
* @details (write detailed description here)
*
*/
static void freeSession(MXS_ROUTER* router_instance, MXS_ROUTER_SESSION* router_client_ses)
{
ROUTER_INSTANCE* router = (ROUTER_INSTANCE *) router_instance;
ROUTER_CLIENT_SES* router_cli_ses = (ROUTER_CLIENT_SES *) router_client_ses;
ss_debug(int prev_val = ) atomic_add(&router_cli_ses->backend->connections, -1);
ss_dassert(prev_val > 0);
MXS_FREE(router_cli_ses);
}
/**
* Close a session with the router, this is the mechanism
* by which a router may cleanup data structure etc.
*
* @param instance The router instance data
* @param router_session The session being closed
*/
static void
closeSession(MXS_ROUTER *instance, MXS_ROUTER_SESSION *router_session)
{
ROUTER_CLIENT_SES *router_cli_ses = (ROUTER_CLIENT_SES *) router_session;
DCB* backend_dcb;
CHK_CLIENT_RSES(router_cli_ses);
/**
* Lock router client session for secure read and update.
*/
if (rses_begin_locked_router_action(router_cli_ses))
{
/* decrease server current connection counter */
backend_dcb = router_cli_ses->backend_dcb;
router_cli_ses->backend_dcb = NULL;
router_cli_ses->rses_closed = true;
/** Unlock */
rses_end_locked_router_action(router_cli_ses);
/**
* Close the backend server connection
*/
if (backend_dcb != NULL)
{
CHK_DCB(backend_dcb);
dcb_close(backend_dcb);
}
}
}
/** Log routing failure due to closed session */
static void log_closed_session(mxs_mysql_cmd_t mysql_command, bool is_closed,
SERVER_REF *ref, bool valid)
{
char msg[MAX_SERVER_ADDRESS_LEN + 200] = ""; // Extra space for message
if (is_closed)
{
sprintf(msg, "Session is closed.");
}
else if (SERVER_IS_DOWN(ref->server))
{
sprintf(msg, "Server '%s' is down.", ref->server->name);
}
else if (SERVER_IN_MAINT(ref->server))
{
sprintf(msg, "Server '%s' is in maintenance.", ref->server->name);
}
else if (!valid)
{
sprintf(msg, "Server '%s' no longer qualifies as a target server.",
ref->server->name);
}
MXS_ERROR("Failed to route MySQL command %d to backend server. %s",
mysql_command, msg);
}
/**
* Check if the server we're connected to is still valid
*
* @param inst Router instance
* @param router_cli_ses Router session
*
* @return True if the backend connection is still valid
*/
static inline bool connection_is_valid(ROUTER_INSTANCE* inst, ROUTER_CLIENT_SES* router_cli_ses)
{
bool rval = false;
if (SERVER_IS_RUNNING(router_cli_ses->backend->server) &&
(router_cli_ses->backend->server->status & inst->bitmask & inst->bitvalue))
{
if ((inst->bitvalue == SERVER_MASTER) && router_cli_ses->backend->active)
{
// If we're using an active master server, verify that it is still a master
rval = router_cli_ses->backend == get_root_master(inst->service->dbref);
}
else
{
/**
* Either we don't use master type servers or the server reference
* is deactivated. We let deactivated connection close gracefully
* so we simply assume it is OK. This allows a server to be taken
* out of use in a manner that won't cause errors to the connected
* clients.
*/
rval = true;
}
}
return rval;
}
/**
* We have data from the client, we must route it to the backend.
* This is simply a case of sending it to the connection that was
* chosen when we started the client session.
*
* @param instance The router instance
* @param router_session The router session returned from the newSession call
* @param queue The queue of data buffers to route
* @return if succeed 1, otherwise 0
*/
static int
routeQuery(MXS_ROUTER *instance, MXS_ROUTER_SESSION *router_session, GWBUF *queue)
{
ROUTER_INSTANCE *inst = (ROUTER_INSTANCE *) instance;
ROUTER_CLIENT_SES *router_cli_ses = (ROUTER_CLIENT_SES *) router_session;
int rc = 0;
DCB* backend_dcb;
MySQLProtocol *proto = (MySQLProtocol*)router_cli_ses->client_dcb->protocol;
mxs_mysql_cmd_t mysql_command = proto->current_command;
bool rses_is_closed;
inst->stats.n_queries++;
// Due to the streaming nature of readconnroute, this is not accurate
atomic_add_uint64(&router_cli_ses->backend->server->stats.packets, 1);
/** Dirty read for quick check if router is closed. */
if (router_cli_ses->rses_closed)
{
rses_is_closed = true;
}
else
{
/**
* Lock router client session for secure read of DCBs
*/
rses_is_closed = !(rses_begin_locked_router_action(router_cli_ses));
}
if (!rses_is_closed)
{
backend_dcb = router_cli_ses->backend_dcb;
/** unlock */
rses_end_locked_router_action(router_cli_ses);
}
bool valid;
char* trc = NULL;
if (rses_is_closed || backend_dcb == NULL ||
(valid = !connection_is_valid(inst, router_cli_ses)))
{
log_closed_session(mysql_command, rses_is_closed, router_cli_ses->backend, valid);
gwbuf_free(queue);
goto return_rc;
}
switch (mysql_command)
{
case MXS_COM_CHANGE_USER:
rc = backend_dcb->func.auth(backend_dcb, NULL, backend_dcb->session,
queue);
break;
case MXS_COM_QUERY:
if (MXS_LOG_PRIORITY_IS_ENABLED(LOG_INFO))
{
trc = modutil_get_SQL(queue);
}
default:
rc = backend_dcb->func.write(backend_dcb, queue);
break;
}
MXS_INFO("Routed [%s] to '%s'%s%s",
STRPACKETTYPE(mysql_command),
backend_dcb->server->name,
trc ? ": " : ".",
trc ? trc : "");
MXS_FREE(trc);
return_rc:
return rc;
}
/**
* Display router diagnostics
*
* @param instance Instance of the router
* @param dcb DCB to send diagnostics to
*/
static void
diagnostics(MXS_ROUTER *router, DCB *dcb)
{
ROUTER_INSTANCE *router_inst = (ROUTER_INSTANCE *) router;
const char *weightby = serviceGetWeightingParameter(router_inst->service);
dcb_printf(dcb, "\tNumber of router sessions: %d\n",
router_inst->stats.n_sessions);
dcb_printf(dcb, "\tCurrent no. of router sessions: %d\n",
router_inst->service->stats.n_current);
dcb_printf(dcb, "\tNumber of queries forwarded: %d\n",
router_inst->stats.n_queries);
if (*weightby)
{
dcb_printf(dcb, "\tConnection distribution based on %s "
"server parameter.\n",
weightby);
dcb_printf(dcb,
"\t\tServer Target %% Connections\n");
for (SERVER_REF *ref = router_inst->service->dbref; ref; ref = ref->next)
{
dcb_printf(dcb, "\t\t%-20s %3.1f%% %d\n",
ref->server->name,
(float) ref->weight / 10,
ref->connections);
}
}
}
/**
* Display router diagnostics
*
* @param instance Instance of the router
* @param dcb DCB to send diagnostics to
*/
static json_t* diagnostics_json(const MXS_ROUTER *router)
{
ROUTER_INSTANCE *router_inst = (ROUTER_INSTANCE *)router;
json_t* rval = json_object();
json_object_set_new(rval, "connections", json_integer(router_inst->stats.n_sessions));
json_object_set_new(rval, "current_connections", json_integer(router_inst->service->stats.n_current));
json_object_set_new(rval, "queries", json_integer(router_inst->stats.n_queries));
const char *weightby = serviceGetWeightingParameter(router_inst->service);
if (*weightby)
{
json_object_set_new(rval, "weightby", json_string(weightby));
}
return rval;
}
/**
* Client Reply routine
*
* The routine will reply to client data from backend server
*
* @param instance The router instance
* @param router_session The router session
* @param backend_dcb The backend DCB
* @param queue The GWBUF with reply data
*/
static void
clientReply(MXS_ROUTER *instance, MXS_ROUTER_SESSION *router_session, GWBUF *queue, DCB *backend_dcb)
{
ss_dassert(backend_dcb->session->client_dcb != NULL);
MXS_SESSION_ROUTE_REPLY(backend_dcb->session, queue);
}
/**
* Error Handler routine
*
* The routine will handle errors that occurred in writes.
*
* @param instance The router instance
* @param router_session The router session
* @param message The error message to reply
* @param problem_dcb The DCB related to the error
* @param action The action: ERRACT_NEW_CONNECTION or ERRACT_REPLY_CLIENT
* @param succp Result of action: true if router can continue
*
*/
static void handleError(MXS_ROUTER *instance, MXS_ROUTER_SESSION *router_session, GWBUF *errbuf,
DCB *problem_dcb, mxs_error_action_t action, bool *succp)
{
ss_dassert(problem_dcb->dcb_role == DCB_ROLE_BACKEND_HANDLER);
DCB *client_dcb;
MXS_SESSION *session = problem_dcb->session;
mxs_session_state_t sesstate;
ROUTER_CLIENT_SES *router_cli_ses = (ROUTER_CLIENT_SES *) router_session;
sesstate = session->state;
client_dcb = session->client_dcb;
if (sesstate == SESSION_STATE_ROUTER_READY)
{
CHK_DCB(client_dcb);
client_dcb->func.write(client_dcb, gwbuf_clone(errbuf));
}
if (router_cli_ses && problem_dcb == router_cli_ses->backend_dcb)
{
router_cli_ses->backend_dcb = NULL;
dcb_close(problem_dcb);
}
/** false because connection is not available anymore */
*succp = false;
}
/** to be inline'd */
/**
* @node Acquires lock to router client session if it is not closed.
*
* Parameters:
* @param rses - in, use
*
*
* @return true if router session was not closed. If return value is true
* it means that router is locked, and must be unlocked later. False, if
* router was closed before lock was acquired.
*
*
* @details (write detailed description here)
*
*/
static bool rses_begin_locked_router_action(ROUTER_CLIENT_SES* rses)
{
bool succp = false;
CHK_CLIENT_RSES(rses);
if (rses->rses_closed)
{
goto return_succp;
}
spinlock_acquire(&rses->rses_lock);
if (rses->rses_closed)
{
spinlock_release(&rses->rses_lock);
goto return_succp;
}
succp = true;
return_succp:
return succp;
}
/** to be inline'd */
/**
* @node Releases router client session lock.
*
* Parameters:
* @param rses - <usage>
* <description>
*
* @return void
*
*
* @details (write detailed description here)
*
*/
static void rses_end_locked_router_action(ROUTER_CLIENT_SES* rses)
{
CHK_CLIENT_RSES(rses);
spinlock_release(&rses->rses_lock);
}
static uint64_t getCapabilities(MXS_ROUTER* instance)
{
return RCAP_TYPE_NONE;
}
/********************************
* This routine returns the root master server from MySQL replication tree
* Get the root Master rule:
*
* find server with the lowest replication depth level
* and the SERVER_MASTER bitval
* Servers are checked even if they are in 'maintenance'
*
* @param servers The list of servers
* @return The Master found
*
*/
static SERVER_REF *get_root_master(SERVER_REF *servers)
{
int i = 0;
SERVER_REF *master_host = NULL;
for (SERVER_REF *ref = servers; ref; ref = ref->next)
{
if (ref->active && SERVER_IS_MASTER(ref->server))
{
if (master_host == NULL)
{
master_host = ref;
}
else if (ref->server->depth < master_host->server->depth ||
(ref->server->depth == master_host->server->depth &&
ref->weight > master_host->weight))
{
/**
* This master has a lower depth than the candidate master or
* the depths are equal but this master has a higher weight
*/
master_host = ref;
}
}
}
return master_host;
}