Ubuntu Manpage: pmReconnectContext - reconnect to a PMAPI context

NAME

       pmReconnectContext - reconnect to a PMAPI context

C SYNOPSIS

       #include <pcp/pmapi.h>

       int pmReconnectContext(int handle);

       cc ... -lpcp

DESCRIPTION

As a consequence of network, host or Performance Metrics Collector Daemon (PMCD) failures,
an application's connection to a PMCD may be established and then subsequently lost.

The routine pmReconnectContext allows an application to request that the context
identified by handle should be re-established, provided the associated metrics source is
accessible.

When the source of metrics associated with the context handle is pmcd(1), then to avoid
flooding the system with reconnect requests, pmReconnectContext will only attempt a
reconnection after a suitable delay from the previous unsuccessful attempt to reconnect
this context. This imposed restriction on the reconnect re-try time interval uses an
exponential back-off so that the initial delay is 5 seconds after the first unsuccessful
attempt, then 10 seconds, then 20 seconds, then 40 seconds and then 80 seconds thereafter.

The environment variable PMCD_RECONNECT_TIMEOUT may be used to redefine the back-off
intervals, see PMAPI(3).

Calling pmReconnectContext with a handle identifying a currently connected pmcd(1) context
will cause the connection to be broken before any reconnection is attempted.

If handle identifies a context associated with an archive source of metrics,
pmReconnectContext returns without delay.

If the reconnection succeeds, pmReconnectContext returns handle.

As a side-effect of reconnecting, any derived metrics that have previously been defined
using pmRegisterDerived(3), pmRegisterDerivedMetric(3) or pmLoadDerivedConfig(3) will be
re-processed and re-bound to the available metrics from the reconnected source. The
support of dynamic definition for derived metrics provides one use case where
pmReconnectContext may be called even if the connection to the metrics source has not been
lost.

Note that even in the case of a successful reconnection, pmReconnectContext does not
change the current Performance Metrics Application Programming Interface (PMAPI) context,
so handle remains valid.

When attempting to connect to a remote pmcd(1) on a machine that is booting,
pmReconnectContext could potentially block for a long time until the remote machine
finishes its initialization. pmReconnectContext will abort and return an error if the
connection has not been established after some specified interval has elapsed. The
default interval is 5 seconds. This may be modified by setting PMCD_CONNECT_TIMEOUT in
the environment to a real number of seconds for the desired timeout. This is most useful
in cases where the remote host is at the end of a slow network, requiring longer latencies
to establish the connection correctly.

CAVEAT

       Applications that use gethostbyname(3) should exercise caution because the  static  fields
       in  struct  hostent  may  not  be  preserved  across  some PMAPI(3) calls.  In particular,
       pmNewContext(3) and pmReconnectContext(3) both may call gethostbyname(3) internally.

DIAGNOSTICS

       PM_ERR_NOCONTEXT

              handle does not identify a valid PMAPI context

       -ETIMEDOUT

              The re-try time has not elapsed, or the reconnection is attempted and fails.

ENVIRONMENT