int pmNewContext(int type , const char * name );
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 a comma-separated list of names referring to a set of archive logs ( type is PM_CONTEXT_ARCHIVE ). Each element of the list may either be the base name common to all of the physical files of an archive log or the name of a directory containing archive logs.
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, email@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 , each element of the list of names in 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.
If more than one archive is specified for a type of PM_CONTEXT_ARCHIVE , there are some restrictions on the archives within the set:
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 ). Both the PM_CTXFLAG_SHALLOW and PM_CTXFLAG_EXCLUSIVE 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 a set of archives, 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 set of archives.
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.
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 (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.