On arm, the exact same detection is done in WelsCPUFeatureDetect,
but in the x86 version of that function we use x86 cpuid for getting
the core count, and this is not available on all processors. For the
case when cpuid can't tell the core count, use the NDK function as
higher level API.
The thread lib itself doesn't build properly on android yet, but will
do so soon.
This allows making the WelsMultipleEventsWaitSingleBlocking
function work properly in unix, without polling. If a master
event is provided, the function first waits for a signal on
that event - once such a signal is received, it is assumed that
one of the individual events in the list have been signalled as
well. Then the function can proceed to check each of the semaphores
in the list using sem_trywait to find the first one of them that
has been signalled. Assuming that the master event is signalled
in pair with the other events, one of the sem_trywait calls
should succeed.
The same master event is also used in
WelsMultipleEventsWaitAllBlocking, to keep the semaphore values
in sync across calls to the both functions.
All users of the function passed the value corresponding to
"infinite", and the (currently unused) unix implementation of it
only supported infinite wait as well.
This avoids having to hardcode the names of devices that don't
support neon.
The devices that don't support neon don't run the armv7 variants
of iOS binaries at all - they would need to be built for the armv6
architecture. (Building for armv6 isn't supported at all in
modern iOS SDKs.)
Therefore we can simply use the __ARM_NEON__ built-in compiler
define to check if NEON code is allowed in the current build,
and have the WelsCPUFeatureDetect function return flags accordingly.
The only thing this disallows is doing an armv6 build which would
optionally enable neon code at runtime if run on an armv7 capable
device, but since Apple allows you to build the same binary for
armv7 separately in the same app bundle, and since armv6 building
isn't even possible in the current iOS SDKs, this isn't really a loss.
This is in contrast to the android builds where the armv7 baseline
does not include NEON.
This avoids the risk of namespace collisions for named semaphores
(where the names are global for the whole machine), on platforms
where we strictly don't need to use the named semaphores.
This unifies the event creation interface, even if the event
name itself is unused on windows, allowing use the exact same
code to initialize events regardless of the actual platform.
Some ifdefs still remain in the event initialization code, since
some events are only used on windows.
Typedeffing WELS_EVENT as sem_t* makes the typedef behave similarly
to the windows version (typedeffed as HANDLE), unifying the code
that allocates and uses these event objects (getting rid of
most of the need for separate codepaths and ifdefs).
The caller of the function should not need to know exactly which
implementation of it is being used.
For the variants that don't support detecting the number of cores,
the pNumberOfLogicProcessors parameter can be left untouched
and the caller will use a higher level API for finding it out.
This simplifies all the calling code, and simplifies adding
more implementations of cpu feature detection.
The two different variants of the threadlib basically are
win32 and unix - use _WIN32 to check for this consistently,
instead of occasionally using __GNUC__ to enable the unix
codepath. (__GNUC__ is also defined on mingw, which still is
a windows platform and should use the _WIN32 code.)
When adding the (dwMilliseconds % 1000) * 1000000 part
to ts.tv_nsec, the ts.tv_nsec field can grow larger than one
whole second. Therefore first add all of dwMilliseconds to
the tv_nsec field and add all whole seconds to the tv_sec
field instead - this way we make sure that the tv_nsec field
actually is less than a second.
