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Problem Report 1615 Details

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Report 1615 Actions

    Problem Report Number 1615
    Submitter's Classification Specification problem
    State Resolved
    Resolution Permanent Interpretation (PIN)
    Problem Resolution ID PIN.X.0172
    Raised 1996-10-29 08:00
    Updated 2003-03-13 08:00
    Published 1996-11-14 08:00
    Product Standard Internationalised System Calls and Libraries Extended (UNIX 95)
    Certification Program The Open Brand certification program
    Test Suite VSU version 4.1.0
    Test Identification CAPI.os/procprim/sigaction 13,25,26,27,39
    Specification System Interfaces and Libraries Issue 4 Version 2
    Location in Spec See Problem Text
    Problem Summary PIN4U.00038 This request claims SIGCHLD need not be generated when SA_NOCLDWAIT is used.
    Problem Text
    The question of if a SIGCHLD should be generated when the parent sets up
    a signal handler with SA_NOCLDWAIT set is unspecified in the X/Open
    specification.

    All of the failed tests setup a handler to catch SIGCHLD, similar to:

    struct sigaction act;
    act.sa_flags |= SA_NOCLDWAIT;
    act.sa_sigaction = test_sig_handler;
    sigaction(SIGCHLD, &act, 0);

    These tests all fork a child, and the child process terminates, either
    by calling exit() or sending itself a signal via kill(). The parent then
    expects to see the handler called for SIGCHLD.

    The XSH4v2 specification does not specify when a SIGCHLD signal is to be
    generated. Our implementation generates a SIGCHLD when a process becomes
    a zombie. The sigaction() description of the SA_NOCLDWAIT flag says that
    zombies will not be formed. We therefore believe these tests are testing
    beyond the specification.

    Further comment appealing against initial refusal
    ------------------------------------------------
    We would like to appeal against the decision to refuse req.4.U.00331 against
    VSU CAPIbase/sigaction tests 13, 25-27, and 39.

    The consultant claims that the specification states that a SIGCHLD is
    generated whenever a child process is terminated or stopped and that
    the discussion of the SA_NOCLDWAIT flag is solely in terms of whether
    or not zombie processes are generated. We disagree based on the
    following additional information contained in the XSH4.2 specification
    for exit():

    "If the parent process has set its SA_NOCLDWAIT flag,
    or set SIGCHLD to SIG_IGN, the status will be discarded,
    and the lifetime of the calling process will end
    immediately."

    Given this, we would not expect a SIGCHLD to be generated when the
    SA_NOCLDWAIT flag is set as it is for the tests in question.

    Can you please give this waiver further consideration?
    Test Output
    TEST CASE: sigaction

    TEST PURPOSE #13
    After a call to int sigaction(int sig, const struct
    sigaction *act, struct sigaction *oact) when
    SA_NOCLDWAIT is set in the sa_flags member of the
    structure pointed to by act and sig is SIGCHLD, child
    processes of the calling process shall not be
    transformed into zombie processes when they terminate.
    PREP: Set up action for SIGCHLD
    PREP: fork() a child that does nothing but exit
    ERROR: Timed out waiting for signal
    13 FAIL

    TEST PURPOSE #25
    After a call to int sigaction(int sig, const struct
    sigaction *act, struct sigaction *oact) with
    SA_SIGINFO set in the sa_flags member of the sigaction
    structure pointed to by act and sig equal to SIGCHLD,
    on entry to the signal catching function specified by
    the sa_sigaction member when the child exited the
    si_code member of the structure pointed to by the
    siginfo argument shall contain CLD_EXITED, the si_pid
    member shall contain the child process ID, the
    si_status member shall contain the child's exit value
    and the si_uid member shall contain the real
    user ID of the process that sent the signal.
    PREP: Set up action for SIGCHLD
    PREP: fork() a child that exits normally
    ERROR: Timed out waiting for signal
    25 FAIL

    TEST PURPOSE #26
    After a call to int sigaction(int sig, const struct
    sigaction *act, struct sigaction *oact) with
    SA_SIGINFO set in the sa_flags member of the sigaction
    structure pointed to by act and sig equal to SIGCHLD,
    on entry to the signal catching function specified by
    the sa_sigaction member when the child was killed the
    si_code member of the structure pointed to by the
    siginfo argument shall contain CLD_KILLED, the si_pid
    member shall contain the child process ID, the
    si_status member shall contain the child's
    signal, the si_uid member shall contain the real
    user ID of the process that sent the signal and no
    core file shall be present.
    PREP: Set up action for SIGCHLD
    PREP: fork() a child that kills itself
    PREP: Generate SIGUSR1 from child
    ERROR: Timed out waiting for signal
    26 FAIL

    TEST PURPOSE #27
    If the implementation supports a signal which causes
    abnormal process termination and the generation of a core
    file:
    After a call to int sigaction(int sig, const struct
    sigaction *act, struct sigaction *oact) with
    SA_SIGINFO set in the sa_flags member of the sigaction
    structure pointed to by act and sig equal to SIGCHLD,
    on entry to the signal catching function specified by
    the sa_sigaction member when the child terminated
    abnormally with a signal that causes generation of a core
    file the si_code member of the structure pointed
    to by the siginfo argument shall contain CLD_DUMPED,
    the si_pid member shall contain the child process ID,
    the si_status member shall contain the child's
    signal, the si_uid member shall contain the
    real user ID of the process that sent the signal and a
    core file shall be present.
    PREP: Obtain the configuration parameter
    VSU_SIGNAL_GENERATING_CORE
    PREP: Set up action for SIGCHLD
    PREP: fork() a child that dumps itself
    PREP: generate SIGILL from child
    ERROR: Timed out waiting for signal
    27 FAIL

    TEST PURPOSE #39
    If the implementation supports a signal which causes
    abnormal process termination but does not cause the
    generation of a core file:
    After a call to int sigaction(int sig, const struct
    sigaction *act, struct sigaction *oact) with
    SA_SIGINFO set in the sa_flags member of the sigaction
    structure pointed to by act and sig equal to SIGCHLD,
    on entry to the signal catching function specified by
    the sa_sigaction member when the child terminated
    abnormally with a signal does not cause generation of a core
    file the si_code member of the structure pointed
    to by the siginfo argument shall contain CLD_KILLED,
    the si_pid member shall contain the child process ID,
    the si_status member shall contain the child's
    signal, the si_uid member shall contain the
    real user ID of the process that sent the signal and a
    core file shall not be present.
    PREP: Set up action for SIGCHLD
    PREP: fork() a child that ends abnormally
    PREP: generate SIGALRM from child
    ERROR: Timed out waiting for signal
    39 FAIL

    Review Information

    Review Type TSMA Review
    Start Date null
    Completed null
    Status Complete
    Review Recommendation No Resolution Given
    Review Response
    We recommend this request be refused.

    We believe these tests are correct as written.

    The specification states that a SIGCHLD is generated when a child
    process is terminated or stopped. We believe the spec's
    discussion of SA_NOCLDWAIT is solely in terms of whether zombie
    processes are generated, with no mention of any delta to the need
    to generate the signal.

    Further response
    ----------------
    As written the spec defines two separate mechanisms for controlling
    the consequences of child termination:

    SIGCHLD set to SIG_IGN - do not create zombies, do not signal

    SA_NOCLDWAIT - do not create zombies, do signal

    To our understanding it is existing practice that these mechanisms are
    used by applications to achieve one of these effects and changing
    the semantics of SA_NOCLDWAIT will thus break application portability.
    An application programmer would set SIGCHLD to SIG_IGN if they did not
    wish to receive a signal, and would be rather surprised if SA_NOCLDWAIT
    suddenly starts having that consequence.

    We also don't see the exit() specification text quoted says anything about
    not signalling. From the other bullets in the list that discuss SA_NOCLDWAIT
    what is being referred to here is the impact on wait() and its friends,
    with SIGCHLD generation mentioned. Further, the bullet in that same
    list vis SIGCHLD generation contains no caveat about SA_NOCLDWAIT,

    o If the implementation supports the SIGCHLD
    signal, a SIGCHLD will be sent to the parent process.

    And one final citation, the spec defines SA_NOCLDWAIT (in signal.h) as:

    SA_NOCLDWAIT Causes implementations not to
    create zombie processes on child
    death.

    Again there is no discussion of SIGCHLD here. All in all we see a clear
    black and white distinction between the two mechanisms, and application
    portability significance, and thus no basis for a grey area waiver.

    Review Type Expert Group Review
    Start Date null
    Completed null
    Status Complete
    Review Resolution No Resolution Given
    Review Conclusion
    We agree with the originator that it is a grey area.
    Two statements are in conflict on the exit() page. In a future direction
    these two statements will be moved together, and a note added
    about the generation of SIGCHLD being implementation defined.

    o If the implementation supports the SIGCHLD
    signal, a SIGCHLD will be sent to the parent
    process.
    o If the parent process has set its SA_NOCLDWAIT flag, or
    set SIGCHLD to SIG_IGN, the status will be discarded
    and the lifetime of the calling process will end immediately.
    If SA_NOCLDWAIT is set, it is implementation defined whether
    a SIGCHLD signal will be sent to the parent process.

    Review Type SA Review
    Start Date null
    Completed null
    Status Complete
    Review Resolution Permanent Interpretation (PIN)
    Review Conclusion
    A Permanent Interpretation is granted.

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