sam_hc_callback_register(3) [centos man page]

SAM_HC_CALLBACK_REGISTER(3)			    Corosync Cluster Engine Programmer's Manual 		       SAM_HC_CALLBACK_REGISTER(3)

NAME

       sam_hc_callback_register - Register health check callback

SYNOPSIS

       #include <corosync/sam.h>

       cs_error_t sam_hc_callback_register (sam_hc_callback_t cb);

DESCRIPTION

       The sam_hc_callback_register function is used to register a user provided healthcheck callback.	After calling of this function, the SAM is
       switched from application driven healthchecking to event driven healthchecking.	In this mode, sam_hc_send(3) does not need to be executed.

       The parameter cb is callback function of type sam_hc_callback_t defined as:

	 typedef int (*sam_hc_callback_t)(void);

       This function will be regulargly called and must return 0 if the process is functioning normally, or -1 if the process is executing  abnor-
       mally.  When -1 is returned, the SAM server execute the registered recovery policy.

       A value of NULL can be passed into this function to switch into application driven healthchecking.  cb to NULL.

RETURN VALUE

       This call return CS_OK value if successful, otherwise and error is returned.

ERRORS

       CS_ERR_BAD_HANDLE
	      SAM was not initialized and registered or health checking is in running state

       CS_ERR_LIBRARY
	      internal	library  call  failed. This can occur during fork() or pipe () system calls and the errno variable can be read to retrieve
	      more information.

SEE ALSO

       sam_start(3), sam_stop(3), sam_hc_send(3), sam_register(3),

       CS_ERR_TRY_AGAIN Resource temporarily unavailable

       CS_ERR_INVALID_PARAM Invalid argument

       CS_ERR_ACCESS Permission denied

       CS_ERR_LIBRARY The connection failed

       CS_ERR_INTERRUPT System call inturrupted by a signal

       CS_ERR_NOT_SUPPORTED The requested protocol/functuality not supported

       CS_ERR_MESSAGE_ERROR Incorrect auth message received

       CS_ERR_NO_MEMORY Not enough memory to completed the requested task

corosync Man Page						    12/01/2009					       SAM_HC_CALLBACK_REGISTER(3)

SAM_OVERVIEW(8) 				    Corosync Cluster Engine Programmer's Manual 				   SAM_OVERVIEW(8)

NAME

       sam_overview - Overview of the Simple Availability Manager

OVERVIEW

       The  SAM library provide a tool to check the health of an application.  The main purpose of SAM is to restart a local process when it fails
       to respond to a healthcheck request in a configured time interval.

       During sam_initialize(3), a duplicate copy of the process is created using the fork(3) system call.  This duplicate process  copy  contains
       the logic for executing the SAM server.	The SAM server is responsible for requesting healthchecks from the active process, and controlling
       the lifecycle of the active process when it fails.  If the active process fails to respond to the  healthcheck  request	sent  by  the  SAM
       server,	it  will  be  sent  a  user configurable signal (default SIGTERM) to request shutdown of the application.  After a configured time
       interval, the process will be forcibly killed by being sent a SIGKILL signal.  Once the active process terminates, the SAM server will cre-
       ate a new active process.

       The  Simple  Availability  Manager is meant to be used in conjunction with the cpg service.  Used together, it is possible to restart a cpg
       process that fails healthchecking during operation.

       The main features of SAM include:

	      o  A configurable recovery policy.

	      o  A configurable time interval for health check operations.

	      o  A notification via signal before recovery action is taken.

	      o  A mechanism to indicate to the application the number of times an active process has been created by the SAM server.

	      o  Both application driven health checking and event driven health checking.

Initializing SAM
       The SAM library is initialized by sam_initialize(3).  sam_initalize(3) may only be called once per process.  Calling it more then once  has
       undefined results and is not recommended or tested.

Setting warning callback
       User  configurable signal (default SIGTERM) is sent to the application when a recovery action is planned.  The application can use the sig-
       nal(3) system call to monitor for this signal.

       There are no special constraints on what SAM apis may be called in a warning callback.  After time_interval expires, a  SIGKILL	signal	is
       sent to the active process to force its termination.

Registering the active process
       The  active process is registered with SAM by calling sam_register(3).  This function should only be called one time in a process.  After a
       recovery action is taken, the new active process will begin execution at the next line of code in a user process after sam_register(3).

Enabling event driven healthchecking
       Two types of healthchecking are available to the user.  The first model is one where the user application healthchecks  during  its  normal
       operation.   It	is  never requested to healtcheck, and if the active process doesn't respond within the time interval, the process will be
       restarted.

       A more useful mechanism for healthchecking is event driven healthchecking.  Because this model is directed by the SAM server, It isn't nec-
       essary  to  guess or add timers to the active process to signal a healthcheck operation is successful.  To use event driven healthchecking,
       the sam_hc_callback_register(3) function should be executed.

BUGS

SEE ALSO

       sam_initialize(3),  sam_finalize(3),  sam_start(3),  sam_stop(3),  sam_register(3),  sam_warn_signal_set(3),  sam_hc_send(3),  sam_hc_call-
       back_register(3)

corosync Man Page						    12/01/2009							   SAM_OVERVIEW(8)