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 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.
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
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
attempted and fails.
- PMCD_CONNECT_TIMEOUT
- Timeout period (in seconds) for pmcd(1) connection
attempts.
- 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).