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Diffstat (limited to 'ChangeLog')
| -rw-r--r-- | ChangeLog | 69 |
1 files changed, 12 insertions, 57 deletions
@@ -1,65 +1,20 @@ 2005-03-14 Ross Johnson <ross at callisto.canberra.edu.au> - * pthread_once.c (pthread_once): Downgrade interlocked operations to simple - memory operations where these are protected by the critical section; edit - comments. - -2005-03-13 Ross Johnson <rpj at callisto.canberra.edu.au> - - * pthread_once.c (pthread_once): Completely redesigned; a change was - required to the ABI (pthread_once_t_), and resulting in a version - compatibility index increment. - - NOTES: - The design (based on pseudo code contributed by Gottlob Frege) avoids - creating a kernel object if there is no contention. See URL for details:- - http://sources.redhat.com/ml/pthreads-win32/2005/msg00029.html - This uses late initialisation similar to the technique already used for - pthreads-win32 mutexes and semaphores (from Alexander Terekhov). - - The subsequent cancelation cleanup additions (by rpj) could not be implemented - without sacrificing some of the efficiency in Gottlob's design. In particular, - although each once_control uses it's own event to block on, a global CS is - required to manage it - since the event must be either re-usable or - re-creatable under cancelation. This is not needed in the non-cancelable - design because it is able to mark the event as closed (forever). - - When uncontested, a CS operation is equivalent to an Interlocked operation - in speed. So, in the final design with cancelability, an uncontested - once_control operation involves a minimum of five interlocked operations - (including the LeaveCS operation). - - ALTERNATIVES: - An alternative design from Alexander Terekhov proposed using a named mutex, - as sketched below:- - - if (!once_control) { // May be in TLS - named_mutex::guard guard(&once_control2); - if (!once_control2) { - <init> - once_control2 = true; - } - once_control = true; - } - - A more detailed description of this can be found here:- - http://groups.yahoo.com/group/boost/message/15442 - - [Although the definition of a suitable PTHREAD_ONCE_INIT precludes use of the - TLS located flag, this is not critical.] + * CVS (snapshot-2005-03-08-fixes): Created branch for + back-porting fixes to snapshot 2005-03-08. - There are three primary concerns though:- - 1) The [named] mutex is 'created' even in the uncontended case. - 2) A system wide unique name must be generated. - 3) Win32 mutexes are VERY slow even in the uncontended case. An uncontested - Win32 mutex lock operation can be 50 (or more) times slower than an - uncontested EnterCS operation. + * pthread_once.c (pthread_once): Add cancellability to the + init_routine; remove cancellability elsewhere (by disabling + cancellability around pthread_cond_wait in particular); + the meaning of the 'done' flag is changed but the ABI doesn't + change as a result. - Ultimately, the named mutex trick is making use of the global locks maintained - by the kernel. + * pthread.h (PTHREAD_ONCE_INIT): Change the 'done' flag value + representation (does not change the value - still zero (0)). - * pthread.h (pthread_once_t_): One flag and an event HANDLE added. - (PTHREAD_ONCE_INIT): Additional values included. + * implement.h (PTW32_ONCE_CLEAR): Defined. + (PTW32_ONCE_DONE): Defined. + (PTW32_ONCE_CANCELLED): Defined. 2005-03-08 Ross Johnson <rpj at callisto.canberra.edu.au>
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