View Issue Details
| ID | Project | Category | View Status | Date Submitted | Last Update |
|---|---|---|---|---|---|
| 0000599 | 1003.1(2008)/Issue 7 | System Interfaces | public | 2012-08-08 22:39 | 2024-06-11 08:52 |
| Reporter | mdempsky | Assigned To | ajosey | ||
| Priority | normal | Severity | Comment | Type | Enhancement Request |
| Status | Closed | Resolution | Accepted As Marked | ||
| Name | Matthew Dempsky | ||||
| Organization | OpenBSD | ||||
| User Reference | |||||
| Section | pthread.h, pthread_equal | ||||
| Page Number | N/A | ||||
| Line Number | N/A | ||||
| Interp Status | --- | ||||
| Final Accepted Text | 0000599:0001334 | ||||
| Summary | 0000599: Reserved "no thread" value for pthread_t | ||||
| Description | Some software currently non-portably assumes pthread_t is an int or pointer type and also that they can use "0" to represent an illegal thread value (similar to how -1 is used for an illegal file descriptor value). E.g., from the Chromium code base: #elif defined(OS_POSIX) typedef pthread_t PlatformThreadHandle; const PlatformThreadHandle kNullThreadHandle = 0; typedef pid_t PlatformThreadId; #endif It would be convenient if POSIX were to add a macro or function that could return a pthread_t value that was guaranteed to compare unequal by pthread_equal() to any valid thread ID. | ||||
| Desired Action | Change <pthread.h> to define a constant expression PTHREAD_NULL of type pthread_t. Change pthread_equal() to return true if t1 and t2 are the same thread ID or are both PTHREAD_NULL; it's behavior is undefined if either t1 or t2 are neither a valid thread ID or PTHREAD_NULL. (My intent here is to allow PTHREAD_NULL to be defined simply as "#define PTHREAD_NULL NULL" on systems where pthread_t is a pointer type, but to allow something like "extern const pthread_t PTHREAD_NULL;" on systems where pthread_t is a struct.) | ||||
| Tags | issue8 | ||||
|
|
The proposed text will need to be tightened up a little. Pedantically speaking, "extern const pthread_t PTHREAD_NULL;" does not make PTHREAD_NULL a constant expression -- just because an expression has a const-qualified type doesn't make it a constant expression in C. Also, "#define PTHREAD_NULL NULL" doesn't make PTHREAD_NULL an expression of type pthread_t. The type of NULL is either void* or an integer in C. |
|
|
Good point. So conforming definitions would have to be something like (just examples): #define PTHREAD_NULL ((pthread_t)NULL) // pointer type #define PTHREAD_NULL ((pthread_t)-42) // int type #define PTHREAD_NULL ((pthread_t){ .foo = -1 }) // struct type to ensure proper types and that they can be used in all const expression contexts. |
|
|
Oh, correction, it would need to be #define PTHREAD_NULL ((const pthread_t){ .foo = -1 }) for the struct-typed pthread_t to allow it in static initialization contexts. |
|
|
Does '(locale_t)0' deserve similar treatment? |
|
|
IMO, I don't think (locale_t)0 *needs* such a treatment because (locale_t)0 is already reserved as a distinct value separate from anything duplocale() or newlocale() might return. Adding a define might still be nice though for consistency or for allowing future standards revisions to allow locale_t to be a struct type. |
|
|
The equivalent for locale_t would not have the value 0, since that already has a special meaning. It would be a value that is guaranteed not to compare equal to any valid locale handle (including LC_GLOBAL_LOCALE) nor to (locale_t)0. A suitable name might be LC_INVALID_LOCALE. |
|
|
After line 10403 on page 311 of Issue 7 append: The <pthread.h> header shall define the following compile-time constant expression, valid as an initializer for pthread_t, representing a value that shall not compare equal to the thread ID of any existing thread: PTHREAD_NULL On page 314 line 10548 replace "None." with: Since pthread_t is an opaque type, a definition of PTHREAD_NULL was added to allow for a null value of that type. Some conforming definitions of PTHREAD_NULL could be: For a pointer type: #define PTHREAD_NULL ((pthread_t)NULL) For an integer type: #define PTHREAD_NULL ((pthread_t)-42) For a struct type: #define PTHREAD_NULL ((const pthread_t){ .foo = -1 }) On line 51624 on page 1606 of Issue 7 replace: If either t1 or t2 are not valid thread IDs, the behavior is undefined. with If either t1 or t2 is not a valid thread ID and is not equal to PTHREAD_NULL, the behavior is undefined. |
|
|
When applying this bug I changed foo to __foo as suggested by Rich Felker on the mailing list on 2020-02-26. In my view this is a minor editorial matter that did not warrant reopening the bug. |
| Date Modified | Username | Field | Change |
|---|---|---|---|
| 2012-08-08 22:39 | mdempsky | New Issue | |
| 2012-08-08 22:39 | mdempsky | Status | New => Under Review |
| 2012-08-08 22:39 | mdempsky | Assigned To | => ajosey |
| 2012-08-08 22:39 | mdempsky | Name | => Matthew Dempsky |
| 2012-08-08 22:39 | mdempsky | Organization | => OpenBSD |
| 2012-08-08 22:39 | mdempsky | Section | => pthread.h, pthread_equal |
| 2012-08-08 22:39 | mdempsky | Page Number | => N/A |
| 2012-08-08 22:39 | mdempsky | Line Number | => N/A |
| 2012-08-09 14:25 | wlerch | Note Added: 0001323 | |
| 2012-08-10 18:12 | mdempsky | Note Added: 0001324 | |
| 2012-08-10 18:23 | mdempsky | Note Added: 0001325 | |
| 2012-08-15 16:28 | eblake | Note Added: 0001326 | |
| 2012-08-16 15:15 | mdempsky | Note Added: 0001328 | |
| 2012-08-16 16:09 | geoffclare | Note Added: 0001329 | |
| 2012-08-29 15:58 | msbrown | Note Added: 0001334 | |
| 2012-08-29 15:59 | msbrown | Tag Attached: issue8 | |
| 2012-08-29 16:01 | msbrown | Note Edited: 0001334 | |
| 2012-08-29 16:03 | msbrown | Interp Status | => --- |
| 2012-08-29 16:03 | msbrown | Final Accepted Text | => 0000599:0001334 |
| 2012-08-29 16:03 | msbrown | Status | Under Review => Resolved |
| 2012-08-29 16:03 | msbrown | Resolution | Open => Accepted As Marked |
| 2020-03-20 10:04 | geoffclare | Note Added: 0004799 | |
| 2020-03-20 10:04 | geoffclare | Status | Resolved => Applied |
| 2024-06-11 08:52 | agadmin | Status | Applied => Closed |
