0000153: waitid() return of 0 is ambiguous - Austin Group Defect Tracker

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Category

Severity

Type

Date Submitted

Last Update

0000153

[1003.1(2008)/Issue 7] System Interfaces

Objection

Omission

2009-09-22 09:29

2009-12-07 16:56

Reporter

geoffclare

View Status

public

Assigned To

ajosey

Priority

normal

Resolution

Accepted

Status

Interpretation Required

Name

Geoff Clare

Organization

The Open Group

User Reference

Section

waitid

Page Number

2190

Line Number

69084

Interp Status

Approved

Final Accepted Text

Note: 0000291

Summary

0000153: waitid() return of 0 is ambiguous

Description

The description of waitid() states:

    "If waitid() returns because a child process was found that
    satisfied the conditions indicated by the arguments idtype and
    options, then the structure pointed to by infop shall be filled in
    by the system with the status of the process. The si_signo member
    shall always be equal to SIGCHLD."

However, it does not state what happens to the structure pointed to
by infop when waitid() returns because WNOHANG was specified and
status is not available for any process specified by idtype and id.

Since the return value is zero in both cases, applications need to
examine at least one field of the structure in order to distinguish
between the cases.

Readers might assume that since the standard only says the structure is
filled in for one case, it is left unchanged for the other. However,
existing practice seems to be to zero out the structure (or, at least
the fields I examined - si_signo, si_pid, si_code and si_status).

Since zero is a special value for signal numbers and process IDs, I
propose that the standard should require the si_signo and si_pid fields
to be set to zero.

The word "always" in the last sentence of the above quote is also
a problem: from the context, the intention appears to be that this
statement only applies when waitid() fills in the structure with the
status of a child process, but it could be taken to mean si_signo is
set to SIGCHLD for the no-status-available case as well.

Desired Action

Change

    "... with the status of the process. The si_signo member shall
    always be equal to SIGCHLD."

to

    "... with the status of the process; the si_signo member shall be
    set equal to SIGCHLD. If waitid() returns because WNOHANG was
    specified and status is not available for any process specified by
    idtype and id, then the si_signo and si_pid members of the
    structure pointed to by infop shall be set to zero and the values
    of other members of the structure are unspecified."

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Notes
(0000239) msbrown (manager) 2009-09-24 15:52	"The standard is unclear on this issue, and no conformance distinction can be made between alternative implementations based on this. This is being referred to the sponsor."

(0000291) ajosey (manager) 2009-11-07 07:30	Interpretation response ------------------------ The standard is unclear on this issue, and no conformance distinction can be made between alternative implementations based on this. This is being referred to the sponsor. Rationale: ------------- None. Notes to the Editor (not part of this interpretation): ------------------------------------------------------- Make the change suggested by the submitter

Issue History
Date Modified	Username	Field	Change
2009-09-22 09:29	geoffclare	New Issue
2009-09-22 09:29	geoffclare	Status	New => Under Review
2009-09-22 09:29	geoffclare	Assigned To	=> ajosey
2009-09-22 09:29	geoffclare	Name	=> Geoff Clare
2009-09-22 09:29	geoffclare	Organization	=> The Open Group
2009-09-22 09:29	geoffclare	Section	=> waitid
2009-09-22 09:29	geoffclare	Page Number	=> 2190
2009-09-22 09:29	geoffclare	Line Number	=> 69084
2009-09-22 09:29	geoffclare	Interp Status	=> ---
2009-09-24 15:52	msbrown	Interp Status	--- => Pending
2009-09-24 15:52	msbrown	Note Added: 0000239
2009-09-24 15:52	msbrown	Status	Under Review => Interpretation Required
2009-09-24 15:53	msbrown	Resolution	Open => Accepted
2009-11-07 07:30	ajosey	Note Added: 0000291
2009-11-07 07:30	ajosey	Interp Status	Pending => Proposed
2009-11-07 07:30	ajosey	Final Accepted Text	=> Note: 0000291
2009-12-07 16:56	ajosey	Interp Status	Proposed => Approved

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