pmReconnectContext(3) — Linux manual page



NAME         top

       pmReconnectContext - reconnect to a PMAPI context

C SYNOPSIS         top

       #include <pcp/pmapi.h>

       int pmReconnectContext(int handle);

       cc ... -lpcp

DESCRIPTION         top

       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

       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.

ENVIRONMENT         top

              Timeout period (in seconds) for pmcd(1) connection attempts.

              Redefines the back-off intervals - refer to PMAPI(3).

SEE ALSO         top

       pmcd(1), PMAPI(3), pmLoadDerivedConfig(3), pmNewContext(3),
       pmRegisterDerived(3), pmRegisterDerivedMetric(3) and pmUseContext(3).

DIAGNOSTICS         top


              handle does not identify a valid PMAPI context


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

CAVEAT         top

       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.

COLOPHON         top

       This page is part of the PCP (Performance Co-Pilot) project.
       Information about the project can be found at ⟨⟩.
       If you have a bug report for this manual page, send it to  This page was obtained from the project's upstream
       Git repository ⟨⟩ on
       2020-09-18.  (At that time, the date of the most recent commit that
       was found in the repository was 2020-09-18.)  If you discover any
       rendering problems in this HTML version of the page, or you believe
       there is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to

Performance Co-Pilot                 PCP               PMRECONNECTCONTEXT(3)

Pages that refer to this page: pmnewcontext(3)pmNewContext(3)pmreconnectcontext(3)pmReconnectContext(3)pmregisterderived(3)pmRegisterDerived(3)pmRegisterDerivedMetric(3)