CMake: Cleanup Threads Search

Search Threads upfront, because we configure specific options
that are cached and reused by dependencies in superbuilds. This
brings all `find_package` calls in the same central file before
we start including sub-directories.

Blosc2Config.cmake.in

@@ -12,7 +12,7 @@ endif()
 list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_LIST_DIR}/Modules")
 
 # this section stores which configuration options were set
-set(HAVE_THREADS @Threads_FOUND@)
+set(HAVE_THREADS @HAVE_THREADS@)
 set(HAVE_IPP @HAVE_IPP@)
 set(HAVE_ZLIB_NG @HAVE_ZLIB_NG@)
 set(DEACTIVATE_IPP @DEACTIVATE_IPP@)
@@ -26,16 +26,13 @@ set(PREFER_EXTERNAL_ZSTD @PREFER_EXTERNAL_ZSTD@)
 #   additionally, the Blosc2_..._FOUND variables are used to support
 #   find_package(Blosc2 ... COMPONENTS ... ...)
 #   this enables downstream projects to express the need for specific features.
-if(WIN32)
-    if(HAVE_THREADS)
-        find_dependency(Threads)
-        set(Blosc2_THREADS_FOUND TRUE)
-    else()
-        set(Blosc2_THREADS_FOUND FALSE)
-    endif()
-else()
+set(CMAKE_THREAD_PREFER_PTHREAD TRUE) # pre 3.1
+set(THREADS_PREFER_PTHREAD_FLAG TRUE) # CMake 3.1+
+if(HAVE_THREADS)
     find_dependency(Threads)
     set(Blosc2_THREADS_FOUND TRUE)
+else()
+    set(Blosc2_THREADS_FOUND FALSE)
 endif()
 
 if(NOT DEACTIVATE_IPP AND HAVE_IPP)

CMakeLists.txt

@@ -151,6 +151,21 @@ if(BUILD_LITE)
     set(DEACTIVATE_ZSTD ON)
 endif()
 
+# Threads
+set(CMAKE_THREAD_PREFER_PTHREAD TRUE) # pre 3.1
+set(THREADS_PREFER_PTHREAD_FLAG TRUE) # CMake 3.1+
+if(WIN32)
+    # try to use the system library
+    find_package(Threads)
+else()
+    find_package(Threads REQUIRED)
+endif()
+if(Threads_FOUND)
+    set(HAVE_THREADS ON)
+else()
+    set(HAVE_THREADS OFF)
+endif()
+
 if(PREFER_EXTERNAL_LZ4)
     find_package(LZ4)
 else()

blosc/CMakeLists.txt

@@ -165,23 +165,20 @@ if(NOT DEACTIVATE_ZSTD)
     endif()
 endif()
 
-set(CMAKE_THREAD_PREFER_PTHREAD TRUE) # pre 3.1
-set(THREADS_PREFER_PTHREAD_FLAG TRUE) # CMake 3.1+
+# Threads and dlopen/dlclose
 if(WIN32)
     # try to use the system library
-    find_package(Threads)
-    if(NOT Threads_FOUND)
-        message(STATUS "using the internal pthread library for win32 systems.")
-        list(APPEND SOURCES blosc/win32/pthread.c)
-    else()
+    if(HAVE_THREADS)
         if(CMAKE_VERSION VERSION_LESS 3.1)
             set(LIBS ${LIBS} ${CMAKE_THREAD_LIBS_INIT})
         else()
             set(LIBS ${LIBS} Threads::Threads)
         endif()
+    else()
+        message(STATUS "using the internal pthread library for win32 systems.")
+        list(APPEND SOURCES blosc/win32/pthread.c)
     endif()
 else()
-    find_package(Threads REQUIRED)
     if(CMAKE_VERSION VERSION_LESS 3.1)
         set(LIBS ${LIBS} ${CMAKE_THREAD_LIBS_INIT})
     else()