Content-type: text/html Man page of monitor


Section: Standard C Library Functions (3C)
Updated: 29 Dec 1996
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monitor - prepare process execution profile  


#include <mon.h>

void monitor(int (*lowpc(), int (*highpc)(), WORD *buffer, size_t bufsize, size_t nfunc);  


The monitor() function is an interface to the profil(2) function and is called automatically with default parameters by any program created by the cc(1B) utility with the -p option specified. Except to establish further control over profiling activity, it is not necessary to explicitly call monitor().

When used, monitor() is called at least at the beginning and the end of a program. The first call to monitor() initiates the recording of two different kinds of execution-profile information: execution-time distribution and function call count. Execution-time distribution data is generated by profil() and the function call counts are generated by code supplied to the object file (or files) by cc(1B) -p. Both types of information are collected as a program executes. The last call to monitor() writes this collected data to the output file mon.out.

The name of the file written by monitor() is controlled by the environment variable PROFDIR. If PROFDIR does not exist, the file mon.out is created in the current directory. If PROFDIR exists but has no value, monitor() does no profiling and creates no output file. If PROFDIR is dirname, and monitor() is called automatically by compilation with cc -p, the file created is dirname/pid.progname where progname is the name of the program.

The lowpc and highpc arguments are the beginning and ending addresses of the region to be profiled.

The buffer argument is the address of a user-supplied array of WORD (defined in the header <mon.h>). The buffer argument is used by monitor() to store the histogram generated by profil() and the call counts.

The bufsize argument identifies the number of array elements in buffer.

The nfunc argument is the number of call count cells that have been reserved in buffer. Additional call count cells will be allocated automatically as they are needed.

The bufsize argument should be computed using the following formula:

size_of_buffer =
        sizeof(struct hdr) +
        nfunc * sizeof(struct cnt) +
        ((highpc-lowpc)/BARSIZE) * sizeof(WORD) +
        sizeof(WORD) - 1 ;
bufsize = (size_of_buffer / sizeof(WORD));


lowpc, highpc, nfunc are the same as the arguments to monitor();

BARSIZE is the number of program bytes that correspond to each histogram bar, or cell, of the profil() buffer;

• the hdr and cnt structures and the type WORD are defined in the header <mon.h>.

The default call to monitor() is as follows:

monitor (&eprol, &etext, wbuf, wbufsz, 600);


eprol is the beginning of the user's program when linked with cc -p (see end(3C));

etext is the end of the user's program (see end(3C));

wbuf is an array of WORD with wbufsz elements;

wbufsz is computed using the bufsize formula shown above with BARSIZE of 8;

600 is the number of call count cells that have been reserved in buffer.

These parameter settings establish the computation of an execution-time distribution histogram that uses profil() for the entire program, initially reserves room for 600 call count cells in buffer, and provides for enough histogram cells to generate significant distribution-measurement results. For more information on the effects of bufsize on execution-distribution measurements, see profil(2).  


Example 1: Example to stop execution monitoring and write the results to a file.

To stop execution monitoring and write the results to a file, use the following:

monitor((int (*)())0, (int (*)())0, (WORD *)0, 0, 0);

Use prof to examine the results.  


Additional calls to monitor() after main() has been called and before exit() has been called will add to the function-call count capacity, but such calls will also replace and restart the profil() histogram computation.  


See attributes(5) for descriptions of the following attributes:




cc(1B), profil(2), end(3C), attributes(5), prof(5)




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Time: 02:37:26 GMT, October 02, 2010