Fallback needed for Apple systems without libdispatch

[barracuda156]

There is no libdispatch prior to 10.6; also it is not supported on ppc (i.e. on 10.6 for ppc as well).
A fallback is required.

For the record, using posix compat fixes the build. I am not sure though if is works correctly.

Here is the provisional patch (only defines changed, not the code):

--- src/lib/IlmThread/IlmThreadSemaphore.h.orig	2023-03-28 23:25:15.000000000 +0800
+++ src/lib/IlmThread/IlmThreadSemaphore.h	2023-05-12 06:18:37.000000000 +0800
@@ -18,10 +18,14 @@
 #include "IlmThreadConfig.h"
 #include "IlmThreadNamespace.h"
 
+#if defined(__APPLE__)
+#   include <AvailabilityMacros.h>
+#endif
+
 #if ILMTHREAD_THREADING_ENABLED
 #   if ILMTHREAD_HAVE_POSIX_SEMAPHORES
 #      include <semaphore.h>
-#   elif defined(__APPLE__)
+#   elif defined(__APPLE__) && __MAC_OS_X_VERSION_MIN_REQUIRED > 1050 && !defined(__ppc__)
 #      include <dispatch/dispatch.h>
 #   elif (defined (_WIN32) || defined (_WIN64))
 #      ifdef NOMINMAX
@@ -56,7 +60,7 @@
 
 	mutable sem_t _semaphore;
 
-#elif defined(__APPLE__)
+#elif defined(__APPLE__) && __MAC_OS_X_VERSION_MIN_REQUIRED > 1050 && !defined(__ppc__)
 	mutable dispatch_semaphore_t _semaphore;
 
 #elif (defined (_WIN32) || defined (_WIN64))

--- src/lib/IlmThread/IlmThreadSemaphorePosixCompat.cpp.orig	2023-03-28 23:25:15.000000000 +0800
+++ src/lib/IlmThread/IlmThreadSemaphorePosixCompat.cpp	2023-05-12 07:25:25.000000000 +0800
@@ -12,8 +12,13 @@
 
 #include "IlmThreadConfig.h"
 
+#if defined(__APPLE__)
+#include <AvailabilityMacros.h>
+#endif
+
 #if ILMTHREAD_THREADING_ENABLED
-#if ( !(ILMTHREAD_HAVE_POSIX_SEMAPHORES) && !defined (__APPLE__) && !defined (_WIN32) && !defined (_WIN64) )
+#if (!(ILMTHREAD_HAVE_POSIX_SEMAPHORES) && !defined (_WIN32) && !defined (_WIN64)) && \
+    (!defined (__APPLE__) || (defined(__APPLE__) && (__MAC_OS_X_VERSION_MIN_REQUIRED < 1060 || defined(__ppc__))))
 
 #include "IlmThreadSemaphore.h"
 
--- src/lib/IlmThread/IlmThreadSemaphoreOSX.cpp.orig	2023-03-28 23:25:15.000000000 +0800
+++ src/lib/IlmThread/IlmThreadSemaphoreOSX.cpp	2023-05-12 07:20:32.000000000 +0800
@@ -11,6 +11,9 @@
 //-----------------------------------------------------------------------------
 
 #if defined(__APPLE__) && !ILMTHREAD_HAVE_POSIX_SEMAPHORES
+#include <AvailabilityMacros.h>
+
+#if __MAC_OS_X_VERSION_MIN_REQUIRED > 1050 && !defined(__ppc__)
 
 #include "IlmThreadSemaphore.h"
 #include "Iex.h"
@@ -67,3 +70,4 @@
 ILMTHREAD_INTERNAL_NAMESPACE_SOURCE_EXIT
 
 #endif
+#endif

[meshula]

This seems reasonable. If you submit it as a PR, the CI will tell us if modern systems continue to build, although it won't give us any information about < 10.6 or ppc.

[barracuda156]

This seems reasonable. If you submit it as a PR, the CI will tell us if modern systems continue to build, although it won't give us any information about < 10.6 or ppc.

@meshula I am pretty sure this should not affect newer systems, I opened an issue instead of PR directly because I am not sure this is the best solution. If no better suggestions are there, this fallback is certainly better than a broken build.
I can open a PR then.

[meshula]

Yes, please submit a PR. There might be a better solution, but I don't have any ideas about what that better solution might be.

[barracuda156]

@meshula A potential solution may be using posix semaphores via configure.args-append -DILMTHREAD_HAVE_POSIX_SEMAPHORES=ON, but I do not know if that is supported (and if it will actually work as intended even if it builds). Comments in the code suggest it is not supported on macOS. At the same time, maybe just no one tried.

UPD. Okay, that failed badly. Let us use posix compat.

[cary-ilm]

I believe this issue was resolved in v3.1.8, feel free to reopen if something is still amiss.

[barracuda156]

I believe this issue was resolved in v3.1.8, feel free to reopen if something is still amiss.

Yes, we should be good here.

Are versions 2.x still maintained btw? Backporting the fix will be nice, if so. (Otherwise we can do it locally. Relevant since there are some ports depending on an older openexr.)

[cary-ilm]

We don't actively support 2.x releases any more, but if it cleans things up on your end I can make a release, let me know.

[barracuda156]

@cary-ilm It would be helpful in fact to backport this, since old version is still in use and looks like will be for quite a while: #1596