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pmNewContext

NAME

pmNewContext - establish a new PMAPI context

C SYNOPSIS

#include <pcp/pmapi.h>

int pmNewContext(int type, const char *name)

cc ... -lpcp

DESCRIPTION

An application using the Performance Metrics Application Programming Interface (PMAPI) may manipulate several concurrent contexts, each associated with a source of performance metrics, e.g. pmcd(1) on some host, or an archive log of performance metrics as created by pmlogger(1), or a standalone connection on the local host that does not involve pmcd(1).

pmNewContext may be used to establish a new context. The source of the metrics is identified by name, and may be either a host name (typeis PM_CONTEXT_HOST), or the base name for the files of an archive log (typeis PM_CONTEXT_ARCHIVE). In the latter case, name may also be the name of any component file of an archive, e.g. the base name with the suffix .index, .meta, .0, etc.

In the case where type is PM_CONTEXT_LOCAL, name is ignored, and the context uses a standalone connection to the PMDA methods used by pmcd(1). When this type of context is used, the range of accessible performance metrics is constrained to those from the operating system, and optionally the ``proc'' and ``sample'' PMDAs.

In the case where type is PM_CONTEXT_HOST, additional flags can be added to the type to indicate if the connection to pmcd(1) should be deferred (PM_CTXFLAG_SHALLOW) and if the file descriptor, used to communicate with pmcd(1), should not be shared across contexts (PM_CTXFLAG_EXCLUSIVE).

The initial instance profile is set up to select all instances in all instance domains. In the case of an archive, the initial collection time is also set to zero, so that an initial pmFetch(3) will result in the earliest set of metrics being returned from the archive.

Once established, the association between a context and a source of metrics is fixed for the life of the context, however routines are provided to independently manipulate both the instance profile (see pmAddProfile(3) and pmDelProfile(3)) and the collection time for archives (see pmSetMode(3)).

pmNewContext returns a handle that may be used with subsequent calls to pmUseContext(3).

The new context remains the current PMAPI context for all subsequent calls across the PMAPI, until another call to pmNewContext(3) is made, or the context is explicitly changed with a call to pmDupContext(3) or pmUseContext(3), or destroyed using pmDestroyContext(3).

When attempting to connect to a remote pmcd(1) on a machine that is booting, pmNewContext could potentially block for a long time until the remote machine finishes its initialization. pmNewContext 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_PORT

TCP/IP port(s) for connecting to pmcd(1), historically was 4321 and more recently the officially registered port 44321; in the current release, pmcd listens on both these ports as a transitional arrangement. If used, should be set to a comma-separated list of numerical port numbers.

PMDA_LOCAL_PROC

If set, then a context established with the type of PM_CONTEXT_LOCAL will have access to the ``proc'' PMDA to retrieve performance metrics about individual processes.

PMDA_LOCAL_SAMPLE

If set, then a context established with the type of PM_CONTEXT_LOCAL will have access to the ``sample'' PMDA if this optional PMDA has been installed locally.

PMDA_PATH

When searching for PMDAs to be loaded when type is PM_CONTEXT_LOCAL, the PMDA_PATH environment variable may be used to define a search path of directories to be used to locate the PMDA executables. The default search path is $PCP_SHARE_DIR/lib:/usr/pcp/lib.

CAVEATS

When using a type of PM_CONTEXT_LOCAL, the operating system PMDA may export data structures directly from the kernel, which means that the pmNewContext caller should be an executable program compiled for the same object code format as the booted IRIX kernel.

Applications that use gethostbyname(3N) should exercise caution because the static fields in struct hostent may not be preserved across some PMAPI(4) calls. In particular, pmNewContext(3) and pmReconnectContext(3) both may call gethostbyname(3N) internally.

SEE ALSO

pmAddProfile(3), PMAPI(3), pmDelProfile(3), pmDestroyContext(3), pmDupContext(3), pmGetConfig(3), pmReconnectContext(3), pmSetMode(3), pmUseContext(3), pmWhichContext(3), pcp.conf(4) and pcp.env(4).

DIAGNOSTICS

PM_ERR_PERMISSION

No permission to perform requested operation

PM_ERR_CONNLIMIT

PMCD connection limit for this host exceeded

PM_ERR_NOCONTEXT

Requested context type was not PM_CONTEXT_LOCAL, PM_CONTEXT_HOST or PM_CONTEXT_ARCHIVE.