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 applications 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 PMCD is accessible.
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).
If the reconnection succeeds,
pmReconnectContext returns
handle.
If
handle identifies a context associated with an archive source of
metrics,
pmReconnectContext does nothing and returns
handle.
Calling
pmReconnectContext with a handle identifying a currently
connected context will cause the connection to be broken before any
reconnection is attempted.
Note that even in the case of a successful reconnection,
pmReconnectContext does not change the current Performance Metrics
Application Programming Interface (PMAPI) context.
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¶
- PMCD_CONNECT_TIMEOUT
- Timeout period (in seconds) for pmcd(1) connection attempts.
- PMCD_RECONNECT_TIMEOUT
- Redefines the back-off intervals - refer to PMAPI(3).
SEE ALSO¶
pmcd(1),
PMAPI(3),
pmNewContext(3) and
pmUseContext(3).
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.
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.