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NAME | C SYNOPSIS | DESCRIPTION | CAVEAT | DIAGNOSTICS | ENVIRONMENT | SEE ALSO | COLOPHON |
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PMRECONNECTCONTEXT(3) Library Functions Manual PMRECONNECTCONTEXT(3)
pmReconnectContext - reconnect to a PMAPI context
#include <pcp/pmapi.h>
int pmReconnectContext(int handle);
cc ... -lpcp
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 re‐
quests, pmReconnectContext will only attempt a reconnection after
a suitable delay from the previous unsuccessful attempt to recon‐
nect 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 re‐
define 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 recon‐
nected source. The support of dynamic definition for derived met‐
rics 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, pmRecon‐
nectContext does not change the current Performance Metrics Appli‐
cation 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. pmRe‐
connectContext 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 num‐
ber of seconds for the desired timeout. This is most useful in
cases where the remote host is at the end of a slow network, re‐
quiring longer latencies to establish the connection correctly.
Applications that use gethostbyname(3) should exercise caution be‐
cause 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.
PM_ERR_NOCONTEXT
handle does not identify a valid PMAPI context
-ETIMEDOUT
The re-try time has not elapsed, or the reconnection is at‐
tempted and fails.
PMCD_CONNECT_TIMEOUT
Timeout period (in seconds) for pmcd(1) connection at‐
tempts.
PMCD_RECONNECT_TIMEOUT
Redefines the back-off intervals - refer to PMAPI(3).
pmcd(1), PMAPI(3), pmLoadDerivedConfig(3), pmNewContext(3),
pmRegisterDerived(3), pmRegisterDerivedMetric(3) and
pmUseContext(3).
This page is part of the PCP (Performance Co-Pilot) project. In‐
formation about the project can be found at ⟨http://www.pcp.io/⟩.
If you have a bug report for this manual page, send it to
pcp@groups.io. This page was obtained from the project's upstream
Git repository ⟨https://github.com/performancecopilot/pcp.git⟩ on
2025-08-11. (At that time, the date of the most recent commit
that was found in the repository was 2025-08-11.) 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 man-pages@man7.org
Performance Co-Pilot PCP PMRECONNECTCONTEXT(3)
Pages that refer to this page: pmnewcontext(3), pmreconnectcontext(3), pmregisterderived(3)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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