Provided by: libpcp3-dev_3.10.8build1_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.