The following issue has been SUBMITTED.
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http://austingroupbugs.net/view.php?id=1216
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Reported By: mikecrowe
Assigned To: ajosey
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Project: 1003.1(2008)/Issue 7
Issue ID: 1216
Category: System Interfaces
Type: Enhancement Request
Severity: Comment
Priority: normal
Status: Under Review
Name: Mike Crowe
Organization:
User Reference:
Section: pthread
Page Number: 0
Line Number: 0
Interp Status: ---
Final Accepted Text:
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Date Submitted: 2018-11-26 18:53 UTC
Last Modified: 2018-11-26 18:53 UTC
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Summary: Adding clockid parameter to functions that accept
absolute struct timespec timeouts
Description:
POSIX contains several functions that support waiting with an absolute
timeout passed as a struct timespec. This time must almost always be
measured against CLOCK_REALTIME. (pthread_cond_timedwait also supports a
single alternative clock specified at construction time via
pthread_condattr_setclock.)
Embedded systems and desktop computers may not have a good source of
accurate time, particularly at boot. This can result in CLOCK_REALTIME
warping by a large amount when the real time is known. In such situations,
CLOCK_REALTIME is not a good choice for expressing timeouts. A member of
the Android libc team has reported[1] that this has been the cause of real
world bugs in Android applications. I've worked on software at different
companies where we had to work around this problem.
The C++ standard provides std::condition_variable::wait_until and
std::timed_mutex::try_lock_until methods which support arbitrary clocks.
Current implementations that build upon POSIX convert these clocks to
CLOCK_REALTIME, which can cause race conditions when CLOCK_REALTIME is
warped. The C++ standard requires the clock to be specified at the time of
the wait, which means that pthread_condattr_setclock isn't useful.
The above problems can be solved by adding variants of the affected
functions that take an extra clockid_t parameter to indicate the clock
that
should be used. Initially, implementations would be required to only
support passing CLOCK_REALTIME which would make adding support
straightforward. Support for CLOCK_MONOTONIC would be suggested, and
implementations would be free to support other clocks if they wished.
This proposal is the result of a thread[2] on the mailing list and my
original defect report[3] only covering pthread_cond_timedwait.
Various naming options for the new functions were discussed[4] and the
following names are based on one of the more popular options. In all cases
the clock immediately precedes the timespec timeout.
int
pthread_mutex_clocklock(
pthread_mutex_t *restrict mutex,
clockid_t clock,
const struct timespec *restrict abstime)
int
pthread_rwlock_clockrdlock(
pthread_rwlock_t *restrict rwlock,
clockid_t clock,
const struct timespec *restrict abstime)
int
pthread_rwlock_clockwrlock(
pthread_rwlock_t *restrict rwlock,
clockid_t clock,
const struct timespec *restrict abstime)
int
pthread_cond_clockwait(
pthread_cond_t *restrict cond,
pthread_mutex_t *restrict mutex,
clockid_t clock,
const struct timespec *restrict abstime)
int
sem_clockwait(
sem_t *restrict sem,
clockid_t clock,
const struct timespec *restrict abstime)
ssize_t
mq_clockreceive(
mqd_t mqdes, char *restrict msg_ptr,
size_t msg_len,
unsigned int *restrict msg_prio,
clockid_t clock,
const struct timespec *restrict abs_timeout)
int
mq_clocksend(
mqd_t mqdes, const char *restrict msg_ptr,
size_t msg_len, unsigned int msg_prio,
clockid_t clock,
const struct timespec *restrict abs_timeout)
These functions all behave the same as their "timed" equivalents, but
measure the timeout against the specified clock rather than
CLOCK_REALTIME.
If passed an unsupported clock, these functions indicate failure in the
same way as their "timed" equivalents and return/set errno to ENOTSUP as
required.
Support for a clock by one function does not require that the clock be
supported by any of the others.
[1]
https://www.mail-archive.com/austin-group-l@opengroup.org/msg02902.html
[2]
https://www.mail-archive.com/austin-group-l@opengroup.org/msg02813.html
[3] http://austingroupbugs.net/view.php?id=1164
[4]
https://www.mail-archive.com/austin-group-l@opengroup.org/msg03034.html
Desired Action:
The addition of the above functions, or ones that provide equivalent
functionality.
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Issue History
Date Modified Username Field Change
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2018-11-26 18:53 mikecrowe New Issue
2018-11-26 18:53 mikecrowe Status New => Under Review
2018-11-26 18:53 mikecrowe Assigned To => ajosey
2018-11-26 18:53 mikecrowe Name => Mike Crowe
2018-11-26 18:53 mikecrowe Section => pthread
2018-11-26 18:53 mikecrowe Page Number => 0
2018-11-26 18:53 mikecrowe Line Number => 0
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