Provided by: libpcp3-dev_3.8.12ubuntu1_amd64 
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 (type is PM_CONTEXT_HOST), or the base
name common to all of the physical files of an archive log (type is PM_CONTEXT_ARCHIVE).
For a type of PM_CONTEXT_HOST, in addition to identifying a host the name may also be used
to encode additional optional information in the form of a pmcd(1) port number, a
pmproxy(1) hostname and a proxy port number. For example the name
"app23:14321,4321@firewall.example.com:11111" specifies a connection on port 14321 (or
port 4321 if 14321 is unavailable) to pmcd(1) on the host app23 via port 11111 to
pmproxy(1) on the host firewall.example.com.
For a type of PM_CONTEXT_ARCHIVE, name may also be the name of any of the physical files
of an archive, e.g. myarchive.meta (the metadata file) or myarchive.index (the temporal
index) or myarchive.0 (the first data volume of the archive) or myarchive.0.bz2 or
myarchive.0.bz (the first data volume compressed with bzip2(1)) or myarchive.0.gz or
myarchive.0.Z or myarchive.0.z (the first data volume compressed with gzip(1)),
myarchive.1 or myarchive.3.bz2 or myarchive.42.gz 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'', ``sample'' and ``ib'' 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 encrypted (PM_CTXFLAG_SECURE), deferred
(PM_CTXFLAG_SHALLOW) and if the file descriptor used to communicate with pmcd(1), should
not be shared across contexts (PM_CTXFLAG_EXCLUSIVE). These final two context flags are
now deprecated and ignored.
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_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 kernel.
In addition, applications using a PM_CONTEXT_LOCAL context must be single-threaded because
the various DSO PMDAs may not be thread-safe. This restriction is enforced at the
PMAPI(3), where routines may return the error code PM_ERR_THREAD if the library detects
calls from more than one thread.
Applications that use gethostbyname(3N) 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(3N) internally.
SEE ALSO
pmcd(1), pmproxy(1), pmAddProfile(3), PMAPI(3), pmDelProfile(3), pmDestroyContext(3),
pmDupContext(3), pmGetConfig(3), pmReconnectContext(3), pmSetMode(3), pmUseContext(3),
pmWhichContext(3), pcp.conf(5) and pcp.env(5).
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.