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Problem Report 0200 Details

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    Problem Report Number 0200
    Submitter's Classification Test Suite problem
    State Resolved
    Resolution Test Suite Deficiency (TSD)
    Problem Resolution ID TSD.X.0200
    Raised 1995-01-05 08:00
    Updated 2003-03-13 08:00
    Published 1995-01-18 08:00
    Product Standard Internationalised System Calls and Libraries (XPG4)
    Certification Program The Open Brand certification program
    Test Suite VSX4 version 4.3.4
    Test Identification XOPEN.os/time/clock 1
    Problem Summary TSD4.200 The VSX4 test suite is using clock() in a nonportable manner. Here is a section of code from XOPEN.os/time/clock/clock.c: private void prepare_tests() { . . . (void) clock(); /* when clock is called, ...
    Problem Text
    The VSX4 test suite is using clock() in a nonportable manner.
    Here is a section of code from XOPEN.os/time/clock/clock.c:

    private void
    prepare_tests()
    {
    .
    .
    .
    (void) clock(); /* when clock is called, the value returned is the
    * CPU time used since the last call. This call
    * is initialisation.
    */
    .
    .
    .
    /* waste some user time */

    for (count = 0; count < COUNT_UT; count++)
    {
    PATH_TRACE;
    use_time();
    }
    .
    .
    .
    clock1 = clock();
    .
    .
    .

    The initial invocation of the function (note especially the comment)
    is clearly in conflict with the XPG4 standard:

    "DESCRIPTION

    The {clock()} function returns the implementation's best
    approximation to the processor time used by the process since the
    beginning of an implementation-dependent time related only to the
    process invocation."

    and:

    "APPLICATION USAGE

    In order to measure time spent in a program, the {clock()} function
    should be called at the start of the program and its return value
    subtracted from the value returned by subsequent calls. ..."

    In the test suite results above, we claim that the difference between
    the times is a result of the clock() function being used incorrectly.
    If the test is changed to calculate the value of clock1 by
    subtracting the value returned by clock() prior to the loop from the
    value returned after the loop, the test is successful. Here is
    an example of how the code should be written:

    private void
    prepare_tests()
    {
    .
    .
    .
    clock1 = clock(); /* obtain CPU time before loop */
    .
    .
    .
    /* waste some user time */

    for (count = 0; count < COUNT_UT; count++)
    {
    PATH_TRACE;
    use_time();
    }
    .
    .
    .
    clock1 = clock() - clock1; /* calculate change in CPU time */
    .
    .
    .
    Test Output
    /tset/XOPEN.os/time/clock/T.clock 1 Failed

    Test Description:
    clock() returns the amount of CPU time (in microseconds) used since
    the first call to clock().
    (See PARAMETERS : VSX_CLOCK_ERR below)

    Test Strategy:
    CALL clock() and times(), saving CPU times given by times()
    EXECUTE user and system code, using use_time() and sys_call()
    VERIFY that the value returned by clock() agrees with the increase in
    CPU times given by times() to within VSX_CLOCK_ERR percent

    Test Information:
    CPU time used as given by clock() does not correspond to value given by
    times() within tolerance limits
    CPU time as given by times is 50000 microseconds
    CPU time as given by clock is 90998 microseconds

    Review Information

    Review Type TSMA Review
    Start Date null
    Completed null
    Status Complete
    Review Recommendation No Resolution Given
    Review Response
    The test suite aligns with the statements in XPG3 rather than those
    in XSH4. The CHANGE HISTORY section of XSH4 states that the changes
    made in the Issue 4 update are "functionally equivalent to Issue 3".

    This statement seems to be misleading since in XPG3 it states that:

    "The clock() function returns the amount of CPU time used since the
    first call to clock()"

    and in XSH4 it states that:

    "The clock() function returns .... the processor time used since the
    beginning of ...... time related only to the process invocation."

    The current code follows the strategy defined for XPG3 and needs to be
    aligned with the XSH4 description.

    A permanent waiver is recommended on the basis of a test suite deficiency.

    Review Type SA Review
    Start Date null
    Completed null
    Status Complete
    Review Resolution Test Suite Deficiency (TSD)
    Review Conclusion
    This is an agreed Test Suite Deficiency.

    Problem Reporting System Options:

     

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