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MaxScale/include/maxscale/monitor.hh

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/*
* Copyright (c) 2018 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: 2022-01-01
*
* 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.
*/
#pragma once
/**
* @file include/maxscale/monitor.hh - The public monitor interface
*/
#include <maxscale/ccdefs.hh>
#include <atomic>
#include <mutex>
#include <openssl/sha.h>
#include <maxbase/semaphore.hh>
#include <maxbase/worker.hh>
#include <maxbase/iterator.hh>
#include <maxscale/config.hh>
#include <maxscale/server.hh>
#include <maxscale/protocol/mysql.hh>
class Monitor;
struct DCB;
struct json_t;
struct EXTERNCMD;
/**
* @verbatim
* The "module object" structure for a backend monitor module
*
* Monitor modules monitor the backend databases that MaxScale connects to.
* The information provided by a monitor is used in routing decisions.
* @endverbatim
*
* @see load_module
*/
struct MXS_MONITOR_API
{
/**
* @brief Create the monitor.
*
* This entry point is called once when MaxScale is started, for creating the monitor.
* If the function fails, MaxScale will not start. The returned object must inherit from
* the abstract base monitor class and implement the missing methods.
*
* @param name Configuration name of the monitor
* @param module Module name of the monitor
* @return Monitor object
*/
Monitor* (* createInstance)(const std::string& name, const std::string& module);
};
/**
* The monitor API version number. Any change to the monitor module API
* must change these versions using the rules defined in modinfo.h
*/
#define MXS_MONITOR_VERSION {5, 0, 0}
/**
* Specifies capabilities specific for monitor.
*
* @see enum routing_capability
*
* @note The values of the capabilities here *must* be between 0x0001 0000 0000 0000
* and 0x0080 0000 0000 0000, that is, bits 48 to 55.
*/
enum monitor_capability_t
{
MCAP_TYPE_NONE = 0x0 // TODO: remove once monitor capabilities are defined
};
// Monitor state enum
enum monitor_state_t
{
MONITOR_STATE_STOPPED,
MONITOR_STATE_RUNNING,
};
/* Return type of mon_ping_or_connect_to_db(). */
enum mxs_connect_result_t
{
MONITOR_CONN_EXISTING_OK, /* Existing connection was ok and server replied to ping. */
MONITOR_CONN_NEWCONN_OK, /* No existing connection or no ping reply. New connection created
* successfully. */
MONITOR_CONN_REFUSED, /* No existing connection or no ping reply. Server refused new connection. */
MONITOR_CONN_TIMEOUT /* No existing connection or no ping reply. Timeout on new connection. */
};
/** Monitor events */
enum mxs_monitor_event_t
{
UNDEFINED_EVENT = 0,
MASTER_DOWN_EVENT = (1 << 0), /**< master_down */
MASTER_UP_EVENT = (1 << 1), /**< master_up */
SLAVE_DOWN_EVENT = (1 << 2), /**< slave_down */
SLAVE_UP_EVENT = (1 << 3), /**< slave_up */
SERVER_DOWN_EVENT = (1 << 4), /**< server_down */
SERVER_UP_EVENT = (1 << 5), /**< server_up */
SYNCED_DOWN_EVENT = (1 << 6), /**< synced_down */
SYNCED_UP_EVENT = (1 << 7), /**< synced_up */
DONOR_DOWN_EVENT = (1 << 8), /**< donor_down */
DONOR_UP_EVENT = (1 << 9), /**< donor_up */
NDB_DOWN_EVENT = (1 << 10), /**< ndb_down */
NDB_UP_EVENT = (1 << 11), /**< ndb_up */
LOST_MASTER_EVENT = (1 << 12), /**< lost_master */
LOST_SLAVE_EVENT = (1 << 13), /**< lost_slave */
LOST_SYNCED_EVENT = (1 << 14), /**< lost_synced */
LOST_DONOR_EVENT = (1 << 15), /**< lost_donor */
LOST_NDB_EVENT = (1 << 16), /**< lost_ndb */
NEW_MASTER_EVENT = (1 << 17), /**< new_master */
NEW_SLAVE_EVENT = (1 << 18), /**< new_slave */
NEW_SYNCED_EVENT = (1 << 19), /**< new_synced */
NEW_DONOR_EVENT = (1 << 20), /**< new_donor */
NEW_NDB_EVENT = (1 << 21), /**< new_ndb */
};
enum credentials_approach_t
{
CREDENTIALS_INCLUDE,
CREDENTIALS_EXCLUDE,
};
/**
* The linked list of servers that are being monitored by the monitor module.
*/
class MXS_MONITORED_SERVER
{
public:
class ConnectionSettings
{
public:
std::string username; /**< Monitor username */
std::string password; /**< Monitor password */
int connect_timeout {1}; /**< Connect timeout in seconds for mysql_real_connect */
int write_timeout {1}; /**< Timeout in seconds for each attempt to write to the server.
* There are retries and the total effective timeout value is two
* times the option value. */
int read_timeout {1}; /**< Timeout in seconds to read from the server. There are retries
* and the total effective timeout value is three times the
* option value. */
int connect_attempts {1}; /**< How many times a connection is attempted */
};
MXS_MONITORED_SERVER(SERVER* server);
/**
* Maintenance mode request constants.
*/
static const int NO_CHANGE = 0;
static const int MAINT_OFF = 1;
static const int MAINT_ON = 2;
static const int BEING_DRAINED_OFF = 3;
static const int BEING_DRAINED_ON = 4;
/**
* Ping or connect to a database. If connection does not exist or ping fails, a new connection is created.
* This will always leave a valid database handle in the database->con pointer, allowing the user to call
* MySQL C API functions to find out the reason of the failure.
*
* @param settings Connection settings
* @return Connection status.
*/
mxs_connect_result_t ping_or_connect(const ConnectionSettings& settings);
SERVER* server = nullptr; /**< The server being monitored */
MYSQL* con = nullptr; /**< The MySQL connection */
bool log_version_err = true;
int mon_err_count = 0;
uint64_t mon_prev_status = -1; /**< Status before starting the current monitor loop */
uint64_t pending_status = 0; /**< Status during current monitor loop */
int64_t disk_space_checked = 0; /**< When was the disk space checked the last time */
int status_request = NO_CHANGE; /**< Is admin requesting Maintenance=ON/OFF on the
* server? */
};
#define MAX_MONITOR_USER_LEN 512
#define MAX_MONITOR_PASSWORD_LEN 512
/**
* Representation of the running monitor.
*/
class Monitor
{
public:
Monitor(const std::string& name, const std::string& module);
virtual ~Monitor();
virtual bool configure(const MXS_CONFIG_PARAMETER* params) = 0;
static const int STATUS_FLAG_NOCHECK = 0;
static const int STATUS_FLAG_CHECK = -1;
virtual monitor_state_t state() const = 0;
/**
* Starts the monitor. If the monitor requires polling of the servers, it should create
* a separate monitoring thread.
*
* @param params Parameters for this monitor
*
* @return True, if the monitor could be started, false otherwise.
*/
virtual bool start(const MXS_CONFIG_PARAMETER* params) = 0;
/**
* Stops the monitor.
*/
void stop();
/**
* Write diagnostic information to a DCB.
*
* @param dcb The dcb to write to.
*/
virtual void diagnostics(DCB* dcb) const = 0;
/**
* Return diagnostic information about the monitor
*
* @return A JSON object representing the state of the monitor
* @see jansson.h
*/
virtual json_t* diagnostics_json() const = 0;
/**
* Set disk space threshold setting.
*
* @param dst_setting The disk space threshold as specified in the config file.
* @return True, if the provided string is valid and the threshold could be set.
*/
bool set_disk_space_threshold(const std::string& dst_setting);
void set_interval(int64_t interval);
/**
* Set status of monitored server.
*
* @param srv Server, must be monitored by this monitor.
* @param bit The server status bit to be sent.
* @errmsg_out If the setting of the bit fails, on return the human readable
* reason why it could not be set.
*
* @return True, if the bit could be set.
*/
bool set_server_status(SERVER* srv, int bit, std::string* errmsg_out);
/**
* Clear status of monitored server.
*
* @param srv Server, must be monitored by this monitor.
* @param bit The server status bit to be cleared.
* @errmsg_out If the clearing of the bit fails, on return the human readable
* reason why it could not be cleared.
*
* @return True, if the bit could be cleared.
*/
bool clear_server_status(SERVER* srv, int bit, std::string* errmsg_out);
/**
* Set Monitor timeouts for connect/read/write
*
* @param type The timeout handling type
* @param value The timeout to set
* @param key Timeout setting name
*/
bool set_network_timeout(int, int, const char*);
/**
* Set username used to connect to backends.
*
* @param user The default username to use when connecting
*/
void set_user(const std::string& user);
/**
* Set password used to connect to backends.
*
* @param passwd The password in encrypted form
*/
void set_password(const std::string& passwd);
void set_script_timeout(int value);
void monitor_set_journal_max_age(time_t value);
/**
* Create a list of running servers
*
* @param dest Destination where the string is appended, must be null terminated
* @param len Length of @c dest
* @param approach Whether credentials should be included or not.
*/
void append_node_names(char* dest, int len, int status,
credentials_approach_t approach = CREDENTIALS_EXCLUDE);
void show(DCB* dcb);
const char* const m_name; /**< Monitor instance name. TODO: change to string */
const std::string m_module; /**< Name of the monitor module */
bool m_active {true}; /**< True if monitor exists and has not been "destroyed". */
mutable std::mutex m_lock;
/** Set when admin requests a maintenance status change. */
int check_status_flag = STATUS_FLAG_NOCHECK;
uint64_t m_ticks {0}; /**< Number of performed monitoring intervals */
uint8_t m_journal_hash[SHA_DIGEST_LENGTH]; /**< SHA1 hash of the latest written journal */
MXS_CONFIG_PARAMETER parameters; /**< Configuration parameters */
std::vector<MXS_MONITORED_SERVER*> m_servers; /**< Monitored servers */
protected:
/**
* Stop the monitor. If the monitor uses a polling thread, the thread should be stopped.
*/
virtual void do_stop() = 0;
/**
* Check if the monitor user can execute a query. The query should be such that it only succeeds if
* the monitor user has all required permissions. Servers which are down are skipped.
*
* @param query Query to test with
* @return True on success, false if monitor credentials lack permissions
*/
bool test_permissions(const std::string& query);
/**
* Detect and handle state change events. This function should be called by all monitors at the end
* of each monitoring cycle. The function logs state changes and executes the monitor script on
* servers whose status changed.
*/
void detect_handle_state_changes();
/**
* Is the journal stale?
*
* @return True, if the journal is stale, false otherwise.
*/
bool journal_is_stale() const;
/**
* @brief Called when a server has been added to the monitor.
*
* The default implementation will add the server to associated
* services.
*
* @param server A server.
*/
virtual void server_added(SERVER* server);
/**
* @brief Called when a server has been removed from the monitor.
*
* The default implementation will remove the server from associated
* services.
*
* @param server A server.
*/
virtual void server_removed(SERVER* server);
/**
* Contains monitor base class settings. Since monitors are stopped before a setting change,
* the items cannot be modified while a monitor is running. No locking required.
*/
class Settings
{
public:
int64_t interval {0}; /**< Monitor interval in milliseconds */
std::string script; /**< Script triggered by events */
int script_timeout {0}; /**< Timeout in seconds for the monitor scripts */
uint64_t events {0}; /**< Bitfield of events which trigger the script */
time_t journal_max_age {0}; /**< Maximum age of journal file */
SERVER::DiskSpaceLimits disk_space_limits; /**< Disk space thresholds */
/**
* How often should a disk space check be made at most, in milliseconds. Negative values imply
* disabling. */
int64_t disk_space_check_interval = -1;
MXS_MONITORED_SERVER::ConnectionSettings conn_settings;
};
Settings m_settings;
private:
void add_server(SERVER* server);
void remove_server(SERVER* server);
private:
friend class MonitorManager;
/**
* Configure base class. Called by monitor creation code.
*
* @param params Config parameters
* @return True on success
*/
bool configure_base(const MXS_CONFIG_PARAMETER* params);
/**
* Launch a script
*
* @param ptr The server which has changed state
* @return Return value of the executed script or -1 on error
*/
int launch_script(MXS_MONITORED_SERVER* ptr);
/**
* Launch a command
*
* @param ptr The server which has changed state
* @param cmd The command to execute.
*
* @note All default script variables will be replaced.
*
* @return Return value of the executed script or -1 on error.
*/
int launch_command(MXS_MONITORED_SERVER* ptr, EXTERNCMD* cmd);
/**
* @brief Add a server to a monitor.
*
* Add a server to a monitor, provided the server is not currently
* being monitored by any monitor. Before adding the server to the
* monitor, the monitor is stopped if it is running and after the
* addition it is restarted if it was running.
*
* @param monitor A monitor.
* @param server A server.
*
* @return True, if the monitor was added, false otherwise.
*/
static bool add_server(Monitor* mon, SERVER* server);
/**
* @brief Remove a server from a monitor.
*
* If the server is being monitored by the server, remove it.
* Before removing, the monitor is stopped if it is running and after
* the removal it is restarted if it was running.
*
* @param monitor A monitor.
* @param server A server.
*/
static void remove_server(Monitor* mon, SERVER* server);
/**
* @brief The monitor should populate associated services.
*/
virtual void populate_services();
};
/**
* Monitor configuration parameters names
*/
extern const char CN_BACKEND_CONNECT_ATTEMPTS[];
extern const char CN_BACKEND_CONNECT_TIMEOUT[];
extern const char CN_BACKEND_READ_TIMEOUT[];
extern const char CN_BACKEND_WRITE_TIMEOUT[];
extern const char CN_DISK_SPACE_CHECK_INTERVAL[];
extern const char CN_EVENTS[];
extern const char CN_JOURNAL_MAX_AGE[];
extern const char CN_MONITOR_INTERVAL[];
extern const char CN_SCRIPT[];
extern const char CN_SCRIPT_TIMEOUT[];
/**
* Store the current server status to the previous and pending status
* fields of the monitored server.
*
* @param mserver The monitored server to update
*/
void monitor_stash_current_status(MXS_MONITORED_SERVER* ptr);
/**
* Clear pending status bits in the monitor server
*
* @param mserver The monitored server to update
* @param bit The bits to clear for the server
*/
void monitor_clear_pending_status(MXS_MONITORED_SERVER* mserver, uint64_t bit);
/**
* Set pending status bits in the monitor server
*
* @param mserver The monitored server to update
* @param bit The bits to set for the server
*/
void monitor_set_pending_status(MXS_MONITORED_SERVER* mserver, uint64_t bit);
void monitor_check_maintenance_requests(Monitor* monitor);
bool mon_status_changed(MXS_MONITORED_SERVER* mon_srv);
bool mon_print_fail_status(MXS_MONITORED_SERVER* mon_srv);
/**
* Ping or connect to a database. If connection does not exist or ping fails, a new connection
* is created. This will always leave a valid database handle in @c *ppCon, allowing the user
* to call MySQL C API functions to find out the reason of the failure.
*
* @param sett Connection settings
* @param pServer A server
* @param ppConn Address of pointer to a MYSQL instance. The instance should either be
* valid or NULL.
* @return Connection status.
*/
mxs_connect_result_t mon_ping_or_connect_to_db(const MXS_MONITORED_SERVER::ConnectionSettings& sett,
SERVER& server, MYSQL** ppConn);
bool mon_connection_is_ok(mxs_connect_result_t connect_result);
void mon_log_connect_error(MXS_MONITORED_SERVER* database, mxs_connect_result_t rval);
const char* mon_get_event_name(mxs_monitor_event_t event);
/**
* @brief Hangup connections to failed servers
*
* Injects hangup events for DCB that are connected to servers that are down.
*
* @param monitor Monitor object
*/
void mon_hangup_failed_servers(Monitor* monitor);
/**
* @brief Report query errors
*
* @param db Database where the query failed
*/
void mon_report_query_error(MXS_MONITORED_SERVER* db);
/**
* @brief Convert monitor to JSON
*
* @param monitor Monitor to convert
* @param host Hostname of this server
*
* @return JSON representation of the monitor
*/
json_t* monitor_to_json(const Monitor* monitor, const char* host);
/**
* @brief Convert all monitors to JSON
*
* @param host Hostname of this server
*
* @return JSON array containing all monitors
*/
json_t* monitor_list_to_json(const char* host);
/**
* @brief Get links to monitors that relate to a server
*
* @param server Server to inspect
* @param host Hostname of this server
*
* @return Array of monitor links or NULL if no relations exist
*/
json_t* monitor_relations_to_server(const SERVER* server, const char* host);
/**
* @brief Store a journal of server states
*
* @param monitor Monitor to journal
* @param master The current master server or NULL if no master exists
*/
void store_server_journal(Monitor* monitor, MXS_MONITORED_SERVER* master);
/**
* @brief Load a journal of server states
*
* @param monitor Monitor where journal is loaded
* @param master Set to point to the current master
*/
void load_server_journal(Monitor* monitor, MXS_MONITORED_SERVER** master);
/**
* Find the monitored server representing the server.
*
* @param mon Cluster monitor
* @param search_server Server to search for
* @return Found monitored server or NULL if not found
*/
MXS_MONITORED_SERVER* mon_get_monitored_server(const Monitor* mon, SERVER* search_server);
/**
* Get an array of monitored servers. If a server defined in the config setting is not monitored by
* the given monitor, the returned array will be empty.
*
* @param params Config parameters
* @param key Setting name
* @param mon Monitor which should monitor the servers
* @param error_out Set to true if an error occurs
* @return Output array
*/
std::vector<MXS_MONITORED_SERVER*> mon_config_get_servers(const MXS_CONFIG_PARAMETER* params,
const char* key, const Monitor* mon,
bool* error_out);
// Function for waiting one monitor interval
void monitor_debug_wait();
namespace maxscale
{
/**
* An abstract class which helps implement a monitor based on a maxbase::Worker thread.
*/
class MonitorWorker : public Monitor
, protected maxbase::Worker
{
public:
MonitorWorker(const MonitorWorker&) = delete;
MonitorWorker& operator=(const MonitorWorker&) = delete;
virtual ~MonitorWorker();
/**
* @brief Current state of the monitor.
*
* Since the state is written to by the admin thread, the value returned in other threads cannot be fully
* trusted. The state should only be read in the admin thread or operations launched by the admin thread.
*
* @return @c MONITOR_STATE_RUNNING if the monitor is running,
* @c MONITOR_STATE_STOPPED if the monitor is stopped.
*/
monitor_state_t state() const override final;
/**
* @brief Find out whether the monitor is running.
*
* @return True, if the monitor is running, false otherwise.
*
* @see state().
*/
bool is_running() const
{
return state() == MONITOR_STATE_RUNNING;
}
/**
* @brief Starts the monitor.
*
* - Calls @c has_sufficient_permissions(), if it has not been done earlier.
* - Updates the 'script' and 'events' configuration paramameters.
* - Calls @c configure().
* - Starts the monitor thread.
*
* - Once the monitor thread starts, it will
* - Load the server journal and update @c m_master.
* - Call @c pre_loop().
* - Enter a loop where it, until told to shut down, will
* - Check whether there are maintenance requests.
* - Call @c tick().
* - Call @c process_state_changes()
* - Hang up failed servers.
* - Store the server journal (@c m_master assumed to reflect the current situation).
* - Sleep until time for next @c tick().
* - Call @c post_loop().
*
* @param param The parameters of the monitor.
*
* @return True, if the monitor started, false otherwise.
*/
bool start(const MXS_CONFIG_PARAMETER* params) final;
/**
* @brief Write diagnostics
*
* The implementation should write diagnostic information to the
* provided dcb. The default implementation writes nothing.
*
* @param dcb The dcb to write to.
*/
virtual void diagnostics(DCB* dcb) const;
/**
* @brief Obtain diagnostics
*
* The implementation should create a JSON object and fill it with diagnostics
* information. The default implementation returns an object that is populated
* with the keys 'script' and 'events' if they have been set, otherwise the
* object is empty.
*
* @return An object, if there is information to return, NULL otherwise.
*/
virtual json_t* diagnostics_json() const;
/**
* Get current time from the monotonic clock.
*
* @return Current time
*/
static int64_t get_time_ms();
protected:
MonitorWorker(const std::string& name, const std::string& module);
void do_stop() final;
/**
* @brief Should the monitor shut down?
*
* @return True, if the monitor should shut down, false otherwise.
*/
bool should_shutdown() const
{
return atomic_load_int32(&m_shutdown) != 0;
}
/**
* @brief Should the disk space status be updated.
*
* @param pMonitored_server The monitored server in question.
*
* @return True, if the disk space should be checked, false otherwise.
*/
bool should_update_disk_space_status(const MXS_MONITORED_SERVER* pMonitored_server) const;
/**
* @brief Update the disk space status of a server.
*
* After the call, the bit @c SERVER_DISK_SPACE_EXHAUSTED will be set on
* @c pMonitored_server->pending_status if the disk space is exhausted
* or cleared if it is not.
*/
void update_disk_space_status(MXS_MONITORED_SERVER* pMonitored_server);
/**
* @brief Configure the monitor.
*
* When the monitor is started, this function will be called in order
* to allow the concrete implementation to configure itself from
* configuration parameters. The default implementation returns true.
*
* @return True, if the monitor could be configured, false otherwise.
*
* @note If false is returned, then the monitor will not be started.
*/
virtual bool configure(const MXS_CONFIG_PARAMETER* pParams);
/**
* @brief Check whether the monitor has sufficient rights
*
* The implementation should check whether the monitor user has sufficient
* rights to access the servers. The default implementation returns True.
*
* @return True, if the monitor user has sufficient rights, false otherwise.
*/
virtual bool has_sufficient_permissions();
/**
* @brief Flush pending server status to each server.
*
* This function is expected to flush the pending status to each server.
* The default implementation simply copies monitored_server->pending_status
* to server->status.
*/
virtual void flush_server_status();
/**
* @brief Monitor the servers
*
* This function is called once per monitor round, and the concrete
* implementation should probe all servers and set server status bits.
*/
virtual void tick() = 0;
/**
* @brief Called before the monitor loop is started
*
* The default implementation does nothing.
*/
virtual void pre_loop();
/**
* @brief Called after the monitor loop has ended.
*
* The default implementation does nothing.
*/
virtual void post_loop();
/**
* @brief Called after tick returns
*
* The default implementation will call @Monitor::detect_state_changes. Overriding functions
* should do the same before proceeding with their own processing.
*/
virtual void process_state_changes();
/**
* Should a monitor tick be ran immediately? The base class version always returns false. A monitor can
* override this to add specific conditions. This function is called every MXS_MON_BASE_INTERVAL_MS
* (100 ms) by the monitor worker thread, which then runs a monitor tick if true is returned.
*
* @return True if tick should be ran
*/
virtual bool immediate_tick_required() const;
Monitor* m_monitor; /**< The generic monitor structure. */
MXS_MONITORED_SERVER* m_master; /**< Master server */
private:
std::atomic<bool> m_thread_running; /**< Thread state. Only visible inside MonitorInstance. */
int32_t m_shutdown; /**< Non-zero if the monitor should shut down. */
bool m_checked; /**< Whether server access has been checked. */
mxb::Semaphore m_semaphore; /**< Semaphore for synchronizing with monitor thread. */
int64_t m_loop_called; /**< When was the loop called the last time. */
bool pre_run() final;
void post_run() final;
bool call_run_one_tick(Worker::Call::action_t action);
void run_one_tick();
};
class MonitorWorkerSimple : public MonitorWorker
{
public:
MonitorWorkerSimple(const MonitorWorkerSimple&) = delete;
MonitorWorkerSimple& operator=(const MonitorWorkerSimple&) = delete;
protected:
MonitorWorkerSimple(const std::string& name, const std::string& module)
: MonitorWorker(name, module)
{
}
/**
* @brief Update server information
*
* The implementation should probe the server in question and update
* the server status bits.
*/
virtual void update_server_status(MXS_MONITORED_SERVER* pMonitored_server) = 0;
/**
* @brief Called right at the beginning of @c tick().
*
* The default implementation does nothing.
*/
virtual void pre_tick();
/**
* @brief Called right before the end of @c tick().
*
* The default implementation does nothing.
*/
virtual void post_tick();
private:
/**
* @brief Monitor the servers
*
* This function is called once per monitor round and will for each server:
*
* - Do nothing, if the server is in maintenance.
* - Store the previous status of the server.
* - Set the pending status of the monitored server object
* to the status of the corresponding server object.
* - Ensure that there is a connection to the server.
* If there is, @c update_server_status() is called.
* If there is not, the pending status will be updated accordingly and
* @c update_server_status() will *not* be called.
* - After the call, update the error count of the server if it is down.
*/
void tick(); // final
};
/**
* The purpose of the template MonitorApi is to provide an implementation
* of the monitor C-API. The template is instantiated with a class that
* provides the actual behaviour of a monitor.
*/
template<class MonitorInstance>
class MonitorApi
{
public:
MonitorApi() = delete;
MonitorApi(const MonitorApi&) = delete;
MonitorApi& operator=(const MonitorApi&) = delete;
static Monitor* createInstance(const std::string& name, const std::string& module)
{
MonitorInstance* pInstance = NULL;
MXS_EXCEPTION_GUARD(pInstance = MonitorInstance::create(name, module));
return pInstance;
}
static MXS_MONITOR_API s_api;
};
template<class MonitorInstance>
MXS_MONITOR_API MonitorApi<MonitorInstance>::s_api =
{
&MonitorApi<MonitorInstance>::createInstance,
};
}
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