On 11/ 2/13 12:39 AM, Keith Packard wrote:
Alan Coopersmith <alan.coopersm...@oracle.com> writes:
What about platforms which don't have <linux/futex.h> ?
I looked into alternate synchronization mechanisms; I couldn't figure
out how to use standard pthread APIs to provide the desired semantics.
Here's the detailed write up I did that describes the SyncFence
semantics and how those map directly to Linux Futexes:
http://keithp.com/blogs/Shared_Memory_Fences/
If you can figure out how to build this with pthread mutexes and/or
semaphores, then we could create a version of xshmfence that worked
using regular pthread functions. As I understand it, pthread
synchronization primitives are supposed to work across processes that
share memory, even if they use different virtual addresses to reference
the same object.
I've checked with the Solaris kernel & libc folks, and they confirm there's
no problem using the POSIX API's on Solaris - ours are correctly implemented
using uint{16,32,64}_t types so they are the same on 32-bit & 64-bit ABI's,
and they're documented & supported as being compatible across the two.
Specifically they said:
"On Solaris, mutexes in shared memory, shared among 32-bit and 64-bit
processes, work correctly. All of the other locking thingies work
correctly too:
condvars
rwlocks
semaphores
barriers
message queues"
And one of our old timers pointed out:
"Note that this is exactly the same problem that Solaris (SunOS first)
solved with the winlock driver.
https://hg.java.net/hg/solaris~on-src/file/tip/usr/src/uts/common/io/winlockio.c#l27
This was an real factor in the excellent performance of sundgadoom 8-)."
(Honestly, I vaguely knew we had winlockio, but not what it was for. Our Xorg
doesn't use it, only our old Xsun implementation with its SUN-DGA extension.)
So between this & the comments from the BSD guys, it seems like POSIX API's
should be the default implementation for all platforms except Linux multi-lib
platforms with incompatible implementations, where you have to use futexes
instead to work around platform bugs.
--
-Alan Coopersmith- alan.coopersm...@oracle.com
Oracle Solaris Engineering - http://blogs.oracle.com/alanc
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