Cleanup cmake thread detection

Remove old variables, prepare for glibc 2.34+ where pthread moves into
libc to detect semaphores.
Force enable C11 for core library to turn on atomics for older compilers
Fix error messages

Signed-off-by: Kimball Thurston <kdt3rd@gmail.com>

cmake/CMakeLists.txt

@@ -100,9 +100,6 @@ endif()
 ###check_include_files(pthread.h ILMTHREAD_HAVE_PTHREAD)
 if(OPENEXR_ENABLE_THREADING AND Threads_FOUND)
   set(ILMTHREAD_THREADING_ENABLED ON)
-  if(CMAKE_HAVE_PTHREAD_H OR CMAKE_USE_PTHREADS_INIT OR CMAKE_HP_PTHREAD_INIT)
-    set(ILMTHREAD_HAVE_PTHREAD ON)
-  endif()
 
   # we have threads, but do we have posix semaphores for sem_init?
   # should be in pthreads
@@ -112,11 +109,15 @@ if(OPENEXR_ENABLE_THREADING AND Threads_FOUND)
     else()
       check_include_files(semaphore.h ILMTHREAD_HAVE_SEMAPHORE_H)
     endif()
-    if(ILMTHREAD_HAVE_SEMAPHORE_H AND ILMTHREAD_HAVE_PTHREAD)
+    if(ILMTHREAD_HAVE_SEMAPHORE_H)
       # should just be in libc, so no need for check_library_exists
-      set(CMAKE_REQUIRED_FLAGS ${CMAKE_THREAD_LIBS_INIT})
-      check_library_exists(pthread sem_init "" ILMTHREAD_HAVE_POSIX_SEMAPHORES)
-      set(CMAKE_REQUIRED_FLAGS)
+      if(CMAKE_HAVE_LIBC_PTHREAD)
+        set(ILMTHREAD_HAVE_POSIX_SEMAPHORES ON)
+      else()
+        set(CMAKE_REQUIRED_FLAGS ${CMAKE_THREAD_LIBS_INIT})
+        check_library_exists(pthread sem_init "" ILMTHREAD_HAVE_POSIX_SEMAPHORES)
+        set(CMAKE_REQUIRED_FLAGS)
+      endif()
     endif()
   endif()
 endif()
@@ -190,10 +191,12 @@ if(OPENEXR_INSTALL_PKG_CONFIG)
     if(OPENEXR_ENABLE_THREADING AND TARGET Threads::Threads)
       # hrm, can't use properties as they end up as generator expressions
       # which don't seem to evaluate
-      if(THREADS_HAVE_PTHREAD_ARG)
-        set(PTHREAD_CFLAGS "-pthread")
+      if(THREADS_HAVE_PTHREAD_ARG OR CMAKE_HAVE_LIBC_PTHREAD)
+        set(exr_pthread_cflags "-pthread")
+      else()
+        set(exr_pthread_cflags "")
       endif()
-      set(PTHREAD_LIBS ${CMAKE_THREAD_LIBS_INIT})
+      set(exr_pthread_libs ${CMAKE_THREAD_LIBS_INIT})
     endif()
     if(NOT zlib_INTERNAL_DIR)
       set(zlib_link "-lz")

cmake/OpenEXR.pc.in

@@ -14,7 +14,7 @@ Name: OpenEXR
 Description: OpenEXR image library
 Version: @OPENEXR_VERSION@
 
-Libs: -L${libdir} -lOpenEXR${libsuffix} -lOpenEXRUtil${libsuffix} -lOpenEXRCore${libsuffix} -lIex${libsuffix} -lIlmThread${libsuffix}
-Cflags: -I${includedir} -I${OpenEXR_includedir}
+Libs: @exr_pthread_libs@ -L${libdir} -lOpenEXR${libsuffix} -lOpenEXRUtil${libsuffix} -lOpenEXRCore${libsuffix} -lIex${libsuffix} -lIlmThread${libsuffix}
+Cflags: -I${includedir} -I${OpenEXR_includedir} @exr_pthread_cflags@
 Requires: Imath
 Libs.private: @zlib_link@

cmake/OpenEXRLibraryDefine.cmake

@@ -14,6 +14,9 @@ function(OPENEXR_DEFINE_LIBRARY libname)
     ${OPENEXR_CURLIB_HEADERS}
     ${OPENEXR_CURLIB_SOURCES})
 
+  # we use atomics internally for the core library, so need C11, but
+  # is only a private requirement
+  target_compile_features(${objlib} PRIVATE c_std_11)
   target_compile_features(${objlib} PUBLIC cxx_std_${OPENEXR_CXX_STANDARD})
   if(OPENEXR_CURLIB_PRIV_EXPORT AND BUILD_SHARED_LIBS)
     target_compile_definitions(${objlib} PRIVATE ${OPENEXR_CURLIB_PRIV_EXPORT})
@@ -32,6 +35,7 @@ function(OPENEXR_DEFINE_LIBRARY libname)
     target_link_libraries(${objlib} PRIVATE ${OPENEXR_CURLIB_PRIVATE_DEPS})
   endif()
   set_target_properties(${objlib} PROPERTIES
+    C_STANDARD_REQUIRED ON
     CXX_STANDARD_REQUIRED ON
     CXX_EXTENSIONS OFF
     POSITION_INDEPENDENT_CODE ON

cmake/OpenEXRSetup.cmake

@@ -21,7 +21,7 @@ set(OPENEXR_CXX_STANDARD "${tmp}" CACHE STRING "C++ standard to compile against"
 set(tmp)
 
 set(OPENEXR_NAMESPACE_CUSTOM "0" CACHE STRING "Whether the namespace has been customized (so external users know)")
-set(OPENEXR_INTERNAL_IMF_NAMESPACE "Imf_${OPENEXR_VERSION_API}" CACHE STRING "Real namespace for Imath that will end up in compiled symbols")
+set(OPENEXR_INTERNAL_IMF_NAMESPACE "Imf_${OPENEXR_VERSION_API}" CACHE STRING "Real namespace for OpenEXR that will end up in compiled symbols")
 set(OPENEXR_IMF_NAMESPACE "Imf" CACHE STRING "Public namespace alias for OpenEXR")
 set(OPENEXR_PACKAGE_NAME "OpenEXR ${OPENEXR_VERSION}${OPENEXR_VERSION_RELEASE_TYPE}" CACHE STRING "Public string / label for displaying package")
 
@@ -148,13 +148,11 @@ endif()
 # so we know how to add the thread stuff to the pkg-config package
 # which is the only (but good) reason.
 if(OPENEXR_ENABLE_THREADING)
-
   if(NOT TARGET Threads::Threads)
-    set(CMAKE_THREAD_PREFER_PTHREAD TRUE)
-    set(THREADS_PREFER_PTHREAD_FLAG TRUE)
+    set(THREADS_PREFER_PTHREAD_FLAG ON)
     find_package(Threads)
     if(NOT Threads_FOUND)
-      message(FATAL_ERROR "Unable to find a threading library which is required for OpenEXR")
+      message(FATAL_ERROR "Unable to find a threading library, disable with OPENEXR_ENABLE_THREADING=OFF")
     endif()
   endif()
 endif()