CMake: Allows setting thread method.

The thread method is now configurable for the CMake build. It matches
the Autotools build by allowing ON (pick the best threading method),
OFF (no threading), posix, win95, and vista. If both Windows and
posix threading are both available, then ON will choose Windows
threading. Windows threading will also not use:

target_link_libraries(liblzma Threads::Threads)

since on systems like MinGW-w64 it would link the posix threads
without purpose.

1 files changed, 104 insertions, 40 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
index d936667f..44be745a 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -178,37 +178,6 @@ if(NOT WIN32 AND NOT DEFINED HAVE_CLOCK_GETTIME)
     endif()
 endif()
 
-
-#############
-# Threading #
-#############
-
-set(THREADS_PREFER_PTHREAD_FLAG TRUE)
-find_package(Threads REQUIRED)
-if(CMAKE_USE_WIN32_THREADS_INIT)
-    if(CMAKE_SIZEOF_VOID_P EQUAL 4)
-        # Define to 1 when using Windows 95 (and thus XP) compatible threads. This
-        # avoids use of features that were added in Windows Vista.
-        # This is used for 32-bit x86 builds for compatibility reasons since it
-        # makes no measurable difference in performance compared to Vista threads.
-        add_compile_definitions(MYTHREAD_WIN95)
-    else()
-        # Define to 1 when using Windows Vista compatible threads. This uses features
-        # that are not available on Windows XP.
-        add_compile_definitions(MYTHREAD_VISTA)
-    endif()
-else()
-    add_compile_definitions(MYTHREAD_POSIX)
-
-    # Check if pthread_condattr_setclock() exists to use CLOCK_MONOTONIC.
-    if(HAVE_CLOCK_MONOTONIC)
-        list(INSERT CMAKE_REQUIRED_LIBRARIES 0 "${CMAKE_THREAD_LIBS_INIT}")
-        check_symbol_exists(pthread_condattr_setclock pthread.h
-                            HAVE_PTHREAD_CONDATTR_SETCLOCK)
-        tuklib_add_definition_if(ALL HAVE_PTHREAD_CONDATTR_SETCLOCK)
-    endif()
-endif()
-
 # Options for new enough GCC or Clang on any arch or operating system:
 if(CMAKE_C_COMPILER_ID MATCHES GNU|Clang)
     # configure.ac has a long list but it won't be copied here:
@@ -227,8 +196,6 @@ add_library(liblzma
     src/common/sysdefs.h
     src/common/tuklib_common.h
     src/common/tuklib_config.h
-    src/common/tuklib_cpucores.c
-    src/common/tuklib_cpucores.h
     src/common/tuklib_integer.h
     src/common/tuklib_physmem.c
     src/common/tuklib_physmem.h
@@ -257,13 +224,10 @@ add_library(liblzma
     src/liblzma/common/easy_preset.h
     src/liblzma/common/filter_common.c
     src/liblzma/common/filter_common.h
-    src/liblzma/common/hardware_cputhreads.c
     src/liblzma/common/hardware_physmem.c
     src/liblzma/common/index.c
     src/liblzma/common/index.h
     src/liblzma/common/memcmplen.h
-    src/liblzma/common/outqueue.c
-    src/liblzma/common/outqueue.h
     src/liblzma/common/stream_flags_common.c
     src/liblzma/common/stream_flags_common.h
     src/liblzma/common/string_conversion.c
@@ -361,6 +325,98 @@ foreach(MF IN LISTS MATCH_FINDERS)
 endforeach()
 
 
+#############
+# Threading #
+#############
+
+# Supported thread methods:
+# ON    - autodetect the best threading method. The autodetection will
+#         prefer Windows threading (win95 or vista) over posix if both are
+#         available. vista threads will be used over win95 unless it is a
+#         32-bit build.
+# OFF   - Disable threading.
+# posix - Use posix threading, or throw an error if not available.
+# win95 - Use Windows win95 threading, or throw an error if not available.
+# vista - Use Windows vista threading, or throw an error if not available.
+set(SUPPORTED_THREAD_METHODS ON OFF posix win95 vista)
+
+set(ENABLE_THREADS ON CACHE STRING
+        "Threading method type to support. Set to 'OFF' to disable threading")
+
+# Create dropdown in CMake GUI since only 1 threading method is possible
+# to select in a build.
+set_property(CACHE ENABLE_THREADS
+        PROPERTY STRINGS "${SUPPORTED_THREAD_METHODS}")
+
+if(NOT ENABLE_THREADS IN_LIST SUPPORTED_THREAD_METHODS)
+    message(SEND_ERROR "'${ENABLE_THREADS}' is not a supported thread type")
+endif()
+
+if(ENABLE_THREADS)
+    # Also set THREADS_PREFER_PTHREAD_FLAG since the flag has no effect
+    # for Windows threading.
+    set(THREADS_PREFER_PTHREAD_FLAG TRUE)
+    find_package(Threads REQUIRED)
+
+    # If both Windows and posix threading are available, prefer Windows.
+    if(CMAKE_USE_WIN32_THREADS_INIT AND NOT ENABLE_THREADS STREQUAL "posix")
+        if(ENABLE_THREADS STREQUAL "win95"
+                OR (ENABLE_THREADS STREQUAL "ON"
+                AND CMAKE_SIZEOF_VOID_P EQUAL 4))
+            # Use Windows 95 (and thus XP) compatible threads.
+            # This avoids use of features that were added in
+            # Windows Vista. This is used for 32-bit x86 builds for
+            # compatibility reasons since it makes no measurable difference
+            # in performance compared to Vista threads.
+            #
+            # The Win95 threading lacks thread-safe one-time initialization
+            # function.
+            if (ENABLE_SMALL)
+                message(SEND_ERROR "Threading method win95 and ENABLE_SMALL "
+                                   "cannot be used at the same time")
+            endif()
+
+            add_compile_definitions(MYTHREAD_WIN95)
+        else()
+            add_compile_definitions(MYTHREAD_VISTA)
+        endif()
+    elseif(CMAKE_USE_PTHREADS_INIT)
+        if(ENABLE_THREADS STREQUAL "posix" OR ENABLE_THREADS STREQUAL "ON")
+            # Overwrite ENABLE_THREADS in case it was set to "ON".
+            # The threading library only needs to be explicitly linked
+            # for posix threads, so this is needed for creating
+            # liblzma-config.cmake later.
+            set(ENABLE_THREADS "posix")
+
+            target_link_libraries(liblzma Threads::Threads)
+            add_compile_definitions(MYTHREAD_POSIX)
+
+            # Check if pthread_condattr_setclock() exists to use CLOCK_MONOTONIC.
+            if(HAVE_CLOCK_MONOTONIC)
+                list(INSERT CMAKE_REQUIRED_LIBRARIES 0 "${CMAKE_THREAD_LIBS_INIT}")
+                check_symbol_exists(pthread_condattr_setclock pthread.h
+                                    HAVE_PTHREAD_CONDATTR_SETCLOCK)
+                tuklib_add_definition_if(ALL HAVE_PTHREAD_CONDATTR_SETCLOCK)
+            endif()
+        else()
+            message(SEND_ERROR
+                    "Windows thread method requested, but a compatible "
+                    "library could not be found")
+        endif()
+    else()
+        message(SEND_ERROR "No supported threading library found")
+    endif()
+
+    target_sources(liblzma PRIVATE
+        src/common/tuklib_cpucores.c
+        src/common/tuklib_cpucores.h
+        src/liblzma/common/hardware_cputhreads.c
+        src/liblzma/common/outqueue.c
+        src/liblzma/common/outqueue.h
+    )
+endif()
+
+
 ############
 # Encoders #
 ############
@@ -438,11 +494,16 @@ if(HAVE_ENCODERS)
         src/liblzma/common/index_encoder.h
         src/liblzma/common/stream_buffer_encoder.c
         src/liblzma/common/stream_encoder.c
-        src/liblzma/common/stream_encoder_mt.c
         src/liblzma/common/stream_flags_encoder.c
         src/liblzma/common/vli_encoder.c
     )
 
+    if(ENABLE_THREADS)
+        target_sources(liblzma PRIVATE
+            src/liblzma/common/stream_encoder_mt.c
+        )
+    endif()
+
     if(SIMPLE_ENCODERS)
         target_sources(liblzma PRIVATE
             src/liblzma/simple/simple_encoder.c
@@ -537,11 +598,16 @@ if(HAVE_DECODERS)
         src/liblzma/common/stream_buffer_decoder.c
         src/liblzma/common/stream_decoder.c
         src/liblzma/common/stream_flags_decoder.c
-        src/liblzma/common/stream_decoder_mt.c
         src/liblzma/common/stream_decoder.h
         src/liblzma/common/vli_decoder.c
     )
 
+    if(ENABLE_THREADS)
+        target_sources(liblzma PRIVATE
+            src/liblzma/common/stream_decoder_mt.c
+        )
+    endif()
+
     if(SIMPLE_DECODERS)
         target_sources(liblzma PRIVATE
             src/liblzma/simple/simple_decoder.c
@@ -660,8 +726,6 @@ endif()
 
 ###
 
-target_link_libraries(liblzma Threads::Threads)
-
 # Put the tuklib functions under the lzma_ namespace.
 target_compile_definitions(liblzma PRIVATE TUKLIB_SYMBOL_PREFIX=lzma_)
 tuklib_cpucores(liblzma)