illumos: manual page: pctx

PCTX_CAPTURE(3CPC) CPU Performance Counters Library Functions

NAME

pctx_capture, pctx_create, pctx_run, pctx_release - process context
library

SYNOPSIS

cc [ flag... ] file... -lpctx [ library... ]
#include <libpctx.h>

typedef void (pctx_errfn_t)(const char *fn, const char *fmt, va_list ap);

pctx_t *pctx_create(const char *filename, char *const *argv, void *arg,
int verbose, pctx_errfn_t *errfn);

pctx_t *pctx_capture(pid_t pid, void *arg, int verbose,
pctx_errfn_t *errfn);

int pctx_run(pctx_t *pctx, uint_t sample, uint_t nsamples,
int (*tick)(pctx *, pid_t, id_t, void *));

void pctx_release(pctx_t *pctx);

DESCRIPTION

This family of functions allows a controlling process (the process that
invokes them) to create or capture controlled processes. The functions
allow the occurrence of various events of interest in the controlled
process to cause the controlled process to be stopped, and to cause
callback routines to be invoked in the controlling process.

pctx_create() and pctx_capture()
There are two ways a process can be acquired by the process context
functions. First, a named application can be invoked with the usual
argv[] array using pctx_create(), which forks the caller and execs the
application in the child. Alternatively, an existing process can be
captured by its process ID using pctx_capture().

Both functions accept a pointer to an opaque handle, arg; this is saved
and treated as a caller-private handle that is passed to the other
functions in the library. Both functions accept a pointer to a
printf(3C)-like error routine errfn; a default version is provided if
NULL is specified.

A freshly-created process is created stopped; similarly, a process that
has been successfully captured is stopped by the act of capturing it,
thereby allowing the caller to specify the handlers that should be called
when various events occur in the controlled process. The set of handlers
is listed on the pctx_set_events(3CPC) manual page.

pctx_run()
Once the callback handlers have been set with pctx_set_events(), the
application can be set running using pctx_run(). This function starts the
event handling loop; it returns only when either the process has exited,
the number of time samples has expired, or an error has occurred (for
example, if the controlling process is not privileged, and the controlled
process has exec-ed a setuid program).

Every sample milliseconds the process is stopped and the tick() routine
is called so that, for example, the performance counters can be sampled
by the caller. No periodic sampling is performed if sample is 0.

pctx_release()
Once pctx_run() has returned, the process can be released and the
underlying storage freed using pctx_release(). Releasing the process will
either allow the controlled process to continue (in the case of an
existing captured process and its children) or kill the process (if it
and its children were created using pctx_create()).

RETURN VALUES

Upon successful completion, pctx_capture() and pctx_create() return a
valid handle. Otherwise, the functions print a diagnostic message and
return NULL.

Upon successful completion, pctx_run() returns 0 with the controlled
process either stopped or exited (if the controlled process has invoked
exit(2).) If an error has occurred (for example, if the controlled
process has exec-ed a set-ID executable, if certain callbacks have
returned error indications, or if the process was unable to respond to
proc(5) requests) an error message is printed and the function returns
-1.

USAGE

Within an event handler in the controlling process, the controlled
process can be made to perform various system calls on its behalf. No
system calls are directly supported in this version of the API, though
system calls are executed by the cpc_pctx family of interfaces in libcpc
such as cpc_pctx_bind_event(3CPC). A specially created agent LWP is used
to execute these system calls in the controlled process. See proc(5) for
more details.

While executing the event handler functions, the library arranges for the
signals SIGTERM, SIGQUIT, SIGABRT, and SIGINT to be blocked to reduce the
likelihood of a keyboard signal killing the controlling process
prematurely, thereby leaving the controlled process permanently stopped
while the agent LWP is still alive inside the controlled process.