переподключиться к контексту PMAPI (reconnect to a PMAPI context)
Имя (Name)
pmReconnectContext - reconnect to a PMAPI context
Синопсис C (C Synopsis)
#include <pcp/pmapi.h>
int pmReconnectContext(int handle);
cc ... -lpcp
Описание (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.
Предостережение (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.
Диагностика (Diagnostic)
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.
Окружение (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).
Смотри также (See also)
pmcd(1), PMAPI(3), pmLoadDerivedConfig(3), pmNewContext(3),
pmRegisterDerived(3), pmRegisterDerivedMetric(3) and
pmUseContext(3).
