NAME
pmtracebegin, pmtraceend, pmtraceabort, pmtracepoint, pmtraceobs,
pmtracecounter, pmtracestate, pmtraceerrstr - application-level
performance instrumentation services
C SYNOPSIS
#include <pcp/trace.h>
int pmtracebegin(const char *tag);
int pmtraceend(const char *tag);
int pmtraceabort(const char *tag);
int pmtracepoint(const char *tag);
int pmtraceobs(const char *tag, double value);
int pmtracecounter(const char *tag, double value);
char *pmtraceerrstr(int code);
int pmtracestate(int flags);
cc ... -lpcp_trace
FORTRAN SYNOPSIS
character*(*) tag
integer code
integer flags
integer state
character*(*) estr
real*8 value
code = pmtracebegin(tag)
code = pmtraceend(tag)
code = pmtraceabort(tag)
code = pmtracepoint(tag)
code = pmtraceobs(tag, value)
code = pmtracecounter(tag, value)
pmtraceerrstr(code, estr)
state = pmtracestate(flags)
f77 ... -lpcp_trace or f90 ... -lpcp_trace
JAVA SYNOPSIS
import sgi.pcp.trace;
int trace.pmtracebegin(String tag);
int trace.pmtraceend(String tag);
int trace.pmtraceabort(String tag);
int trace.pmtracepoint(String tag);
int trace.pmtraceobs(String tag, double value);
int trace.pmtracecounter(String tag, double value);
String trace.pmtraceerrstr(int code);
int trace.pmtracestate(int flags);
DESCRIPTION
The pcp_trace library functions provide a mechanism for identifying
sections of a program as transactions or events for use by the trace
Performance Metrics Domain Agent (refer to pmdatrace(1) and PMDA(3)).
The monitoring of transactions using the Performance Co-Pilot (PCP)
infrastructure is initiated through a call to pmtracebegin. Time will
be recorded from the end of each pmtracebegin call to the start of the
following call to pmtraceend, where the same tag identifier is used in
both calls. Following from this, no visible recording will occur until
at least one call to pmtraceend is made referencing a tag previously
used in a call to pmtracebegin.
A transaction which is currently in progress can be cancelled by
calling pmtraceabort. No transaction data gathered for that particular
transaction will be exported, although data from previous and
subsequent successful transactions with that tag name are still
exported. This is most useful when an error condition arises during
transaction processing and the transaction does not run to completion.
The tag argument to pmtracebegin, pmtraceend and pmtraceabort is used
to uniquely identify each transaction within the pcp_trace library and
later by the trace PMDA as the instance domain identifiers for the
transaction performance metrics which it exports. These routines are
most useful when used around blocks of code which are likely to be
executed a number of times over some relatively long time period (in a
daemon process, for example).
pmtracebegin has two distinct roles - firstly as the initiator of a new
transaction, and secondly as a mechanism for setting a new start time.
Similarly, pmtraceend is used to register a new tag and its initial
state with the trace PMDA, or alternatively to update the statistics
which the PMDA currently associates with the given tag.
A second form of program instrumentation can be obtained from
pmtracepoint. This is a simpler form of monitoring as it exports only
the number of times that a particular point in a program has been
passed. This differs to the transaction monitoring offered by
pmtracebegin and pmtraceend, which exports a running count of
successful transaction completions as well as statistics on the time
interval between the start and end points of each transaction. This
function is most useful when start and end points are not well defined.
Examples of this would be when the code branches in such a way that a
transaction cannot be clearly identified, or when processing does not
follow a transactional model, or the desired instrumentation is akin to
event rates rather than event service times.
The pmtraceobs and pmtracecounter functions have similar semantics to
pmtracepoint, but also allow an arbitrary numeric value to be passed to
the trace PMDA. The most recent value for each tag is then immediately
available from the PMDA. The only difference between pmtraceobs and
pmtracecounter is that the value exported via pmtracecounter is assumed
to be a monotonically increasing counter value (e.g. the number of
bytes read from a socket), whereas the value exported via pmtraceobs
can be any value at all.
pmtracestate allows the application to set state flags which are
honoured by subsequent calls to the pcp_trace library routines. There
are currently two types of flag - debugging flags and the asynchronous
protocol flag. A single call may specify a number of flags together,
combined using a (bitwise) logical OR operation, and overrides the
previous state setting.
The debugging flags to pmtracestate cause pcp_trace to print diagnostic
messages on the standard output stream at important processing points.
The default protocol used between the trace PMDA and individual
pcp_trace client applications is a synchronous protocol, which allows
for dropped connections to be reestablished at a later stage should
this become possible. An asynchronous protocol is also available which
does not provide the reconnection capability, but which does away with
much of the overhead inherent in synchronous communication. This
behaviour can be toggled using the pmtracestate call, but must be
called before other calls to the library. This differs to the
debugging state behaviour, which can be altered at any time.
pmtracestate returns the previous state (setting prior to being
called).
The following table describes each of the pmtracestate flags - examples
of the use of these flags in each supported language are given in the
demo applications (refer to the ‘‘FILES’’ section below).
+------------+-----------------------------------------------+
|State Flags | Semantics |
+------------+-----------------------------------------------+
|0 NONE | Synchronous PDUs and no diagnostics (default) |
|1 API | Shows processing just below the API (debug) |
|2 COMMS | Shows network-related activity (debug) |
|4 PDU | Shows app<->PMDA IPC traffic (debug) |
|8 PDUBUF | Shows internal IPC buffer management (debug) |
|16 NOAGENT | No PMDA communications at all (debug) |
|32 ASYNC | Use the asynchronous PDU protocol (control) |
+------------+-----------------------------------------------+
Should any of the pcp_trace library functions return a negative value,
an error has occured. This can be diagnosed further using the
pmtraceerrstr routine, which takes the negative return value as its
code argument, and in the C-callable interface returns a pointer to the
associated error message. This points into a static error table, and
should therefore not be passed to free(3). The Fortran-callable
interface has a slightly different syntax, requiring the destination
character array to be passed in as the second argument. The Java-
callable interface returns a UTF-8 string, created using the JNI (Java
Native Interface) routine NewStringUTF.
ENVIRONMENT
The pcp_trace routines communicate with the trace PMDA via a socket
connection, which by default uses TCP/IP port number 4323. This can be
over-ridden by setting PCP_TRACE_PORT to a different port number when
the application is started. The host where the trace PMDA is running
is by default the localhost, but this can be changed using
PCP_TRACE_HOST. When attempting to connect to a remote trace PMDA,
after some specified time interval has elapsed, the connection attempt
will be aborted and an error status will be returned. The default
timeout interval is 3 seconds, and this can be modified by setting
PCP_TRACE_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.
NOTES
The pcp_trace Java class interface has been developed and verified
using version 1.1 of the Java Native Interface (JNI) specification.
FILES
$PCP_DEMOS_DIR/trace/*.c
Sample C programs and source for pmtrace(1). Use make(1) to
build these programs.
$PCP_DEMOS_DIR/trace/fapp1.f
Sample Fortran program. Call ‘make fortran77’ or ‘make
fortran90’ to build this program.
$PCP_DEMOS_DIR/trace/japp1.java
Sample Java program. ‘make java’ builds the java class file.
/usr/java/classes/sgi/pcp/trace.java
Java trace class definition.
PCP ENVIRONMENT
Environment variables with the prefix PCP_ are used to parameterize the
file and directory names used by PCP. On each installation, the file
/etc/pcp.conf contains the local values for these variables. The
$PCP_CONF variable may be used to specify an alternative configuration
file, as described in pcp.conf(4). Values for these variables may be
obtained programatically using the pmGetConfig(3) function.
SEE ALSO
file:$PCP_DOC_DIR/Tutorial/trace.html, pcp.man.tutorial, Provided the,
make(1), pmcd(1), pmdatrace(1), pmprobe(1), pmtrace(1), Relevant
information is also available from the on-line PCP Tutorial, subsystem
from the PCP images has been installed, access the URL and from your
web browser.
DIAGNOSTICS
A negative return value from a pcp_trace function indicates that an
error has occured - if this is the case, the return value can be passed
to pmtraceerrstr to obtain the associated error message.
Success is indicated by a return value of zero.
pmtracestate also returns an integer representing the state flags which
were set prior to the call.
CAVEAT
Applications that use gethostbyname(3N) should exercise caution because
the static fields in struct hostent may not be preserved across some
pcp_trace calls. In particular, pmtracebegin, pmtraceend,
pmtracepoint, pmtracecounter, and pmtraceobs may all call
gethostbyname(3N) internally.