On Tue, Feb 23, 2021 at 4:25 AM Heinz Junkes <jun...@fhi-berlin.mpg.de> wrote:
> what I have just never understood > > POSIX Prio 2 ist LOW Priority > RTEMS Prio 1 is HIGH Priority > In general, RTOS threading APIs tended to use 1 as a high priority. The RTEMS Classic API based on pSOS+, VxWorks, and VRTX32 which preceded all those all follow 1 is high priority model. POSIX calls for the opposite range. Not sure why. Interestingly, I had a discussion with the main kernel person for another RTOS about this in a standards meeting and he noted that although every implementation of POSIX threads we both knew about does use low number as low priority, it is not as explicit in the POSIX standard as one would think. We have just all read the same text that way since POSIX is careful to say raises or lowers priority and the implication we all saw is that the numbers follow that languge. But at this point, the priorities run this way for no other reason than history and compatibility. For all I know, it may even be baked into the POSIX Compliance Test Suite. Any program with hard-coded numbers certainly has it baked in. While I am beating this topic mercilessly, let me point out that POSIX only calls for a minimum of 32 priority levels. Portable programs cannot assume more. And the default attribute set for all POSIX threading and synchronization objects is implementation defined. Portable programs should always explicitly set all attributes for pthreads, mutexes, etc. The RTOS choice probably reflects using a bitmap to represent if a thread is present on the FIFO for each priority. This would make a bit index map directly to priority in most cases. This design dates back to at least VMS where you have 32 priority levels because you could scan 32 bits in a single instruction. This was carried forward into Windows NT. THe diversity of choices reminded me of this quote from Andrew Tanenbaum: "The nice thing about standards is that there are so many of them to choose from." In the end different people had an arbitrary decision and picked different answers. Ada task priority is another set of choices. :) --joel > Heinz > > > > On 23. Feb 2021, at 09:17, Sebastian Huber < > sebastian.hu...@embedded-brains.de> wrote: > > > > On 23/02/2021 08:36, Heinz Junkes wrote: > > > >> I would have a similar question ;-) > >> > >> What is the priority of the POSIX_Init - Task (as Posix-Prio)? > > There is no option to configure the priority of the POSIX initialization > thread, so the default priority of 2 is used, see > _POSIX_Threads_Default_attributes. > > > > -- > > embedded brains GmbH > > Herr Sebastian HUBER > > Dornierstr. 4 > > 82178 Puchheim > > Germany > > email: sebastian.hu...@embedded-brains.de > > phone: +49-89-18 94 741 - 16 > > fax: +49-89-18 94 741 - 08 > > > > Registergericht: Amtsgericht München > > Registernummer: HRB 157899 > > Vertretungsberechtigte Geschäftsführer: Peter Rasmussen, Thomas Dörfler > > Unsere Datenschutzerklärung finden Sie hier: > > https://embedded-brains.de/datenschutzerklaerung/ > > > > _______________________________________________ > devel mailing list > devel@rtems.org > http://lists.rtems.org/mailman/listinfo/devel
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