cmake: standardize USE_THREADS and USE_NSEC

Threading can now be disabled with `USE_THREADS=OFF` instead of
`THREADSAFE=OFF` to better support the other cmake semantics.

Nanosecond support is the default _if_ we can detect it.  This should be
our default always - like threads - and people can opt out explicitly.

CMakeLists.txt

@@ -6,7 +6,7 @@ cmake_minimum_required(VERSION 3.5.1)
 project(libgit2 VERSION "1.3.0" LANGUAGES C)
 
 # Add find modules to the path
-set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} "${libgit2_SOURCE_DIR}/cmake/")
+set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} "${libgit2_SOURCE_DIR}/cmake")
 
 # Modules
 
@@ -30,12 +30,15 @@ include(EnableWarnings)
 #
 
 # Optional subsystems
-option(THREADSAFE              "Build libgit2 as threadsafe"                            ON)
 option(BUILD_SHARED_LIBS       "Build Shared Library (OFF for Static)"                  ON)
 option(BUILD_TESTS             "Build Tests using the Clar suite"                       ON)
 option(BUILD_EXAMPLES          "Build library usage example apps"                      OFF)
 option(BUILD_FUZZERS           "Build the fuzz targets"                                OFF)
 
+# Suggested functionality that may not be available on a per-platform basis
+option(USE_THREADS             "Use threads for parallel processing when possible"      ON)
+option(USE_NSEC                "Support nanosecond precision file mtimes and ctimes"    ON)
+
 # Backend selection
 option(USE_SSH                 "Link with libssh2 to enable SSH support"                ON)
 option(USE_HTTPS               "Enable HTTPS support. Can be set to a specific backend" ON)

README.md

@@ -279,7 +279,7 @@ The following CMake variables are declared:
 - `CMAKE_INSTALL_INCLUDEDIR`: Where to install headers to.
 - `BUILD_SHARED_LIBS`: Build libgit2 as a Shared Library (defaults to ON)
 - `BUILD_TESTS`: Build the unit and integration test suites (defaults to ON)
-- `THREADSAFE`: Build libgit2 with threading support (defaults to ON)
+- `USE_THREADS`: Build libgit2 with threading support (defaults to ON)
 
 To list all build options and their current value, you can do the
 following:

cmake/FindStatNsec.cmake

-INCLUDE(FeatureSummary)
+include(FeatureSummary)
 
-CHECK_STRUCT_HAS_MEMBER ("struct stat" st_mtim "sys/types.h;sys/stat.h"
+check_struct_has_member("struct stat" st_mtim "sys/types.h;sys/stat.h"
 	HAVE_STRUCT_STAT_ST_MTIM LANGUAGE C)
-CHECK_STRUCT_HAS_MEMBER ("struct stat" st_mtimespec "sys/types.h;sys/stat.h"
+check_struct_has_member("struct stat" st_mtimespec "sys/types.h;sys/stat.h"
 	HAVE_STRUCT_STAT_ST_MTIMESPEC LANGUAGE C)
-CHECK_STRUCT_HAS_MEMBER("struct stat" st_mtime_nsec sys/stat.h
+check_struct_has_member("struct stat" st_mtime_nsec sys/stat.h
 	HAVE_STRUCT_STAT_MTIME_NSEC LANGUAGE C)
 
-IF (HAVE_STRUCT_STAT_ST_MTIM)
-	CHECK_STRUCT_HAS_MEMBER("struct stat" st_mtim.tv_nsec sys/stat.h
+if(HAVE_STRUCT_STAT_ST_MTIM)
+	check_struct_has_member("struct stat" st_mtim.tv_nsec sys/stat.h
 		HAVE_STRUCT_STAT_NSEC LANGUAGE C)
-ELSEIF (HAVE_STRUCT_STAT_ST_MTIMESPEC)
-	CHECK_STRUCT_HAS_MEMBER("struct stat" st_mtimespec.tv_nsec sys/stat.h
+elseif(HAVE_STRUCT_STAT_ST_MTIMESPEC)
+	check_struct_has_member("struct stat" st_mtimespec.tv_nsec sys/stat.h
 		HAVE_STRUCT_STAT_NSEC LANGUAGE C)
-ELSE ()
-	SET( HAVE_STRUCT_STAT_NSEC ON )
-ENDIF()
+else()
+	set(HAVE_STRUCT_STAT_NSEC ON )
+endif()
 
-IF (HAVE_STRUCT_STAT_NSEC OR WIN32)
-	OPTION( USE_NSEC		"Care about sub-second file mtimes and ctimes"	ON  )
-ELSE()
-	SET(USE_NSEC OFF)
-ENDIF()
-
-ADD_FEATURE_INFO(nanoseconds USE_NSEC "whether to use sub-second file mtimes and ctimes")
+add_feature_info(nanoseconds USE_NSEC "support nanosecond precision file mtimes and ctimes")

docs/error-handling.md

@@ -21,7 +21,7 @@ critical failures (such as a packfile being corrupted, a loose object
 having the wrong access permissions, etc.) all of which will return -1.
 When the object lookup is successful, it will return 0.
 
-If libgit2 was compiled with threads enabled (`-DTHREADSAFE=ON` when using
+If libgit2 was compiled with threads enabled (`-DUSE_THREADS=ON` when using
 CMake), then the error message will be kept in thread-local storage, so it
 will not be modified by other threads.  If threads are not enabled, then
 the error message is in global data.

src/CMakeLists.txt

@@ -81,11 +81,11 @@ if(NEED_LIBRT)
 	list(APPEND LIBGIT2_PC_LIBS "-lrt")
 endif()
 
-if(THREADSAFE)
+if(USE_THREADS)
 	list(APPEND LIBGIT2_LIBS ${CMAKE_THREAD_LIBS_INIT})
 	list(APPEND LIBGIT2_PC_LIBS ${CMAKE_THREAD_LIBS_INIT})
 endif()
-add_feature_info(threadsafe THREADSAFE "threadsafe support")
+add_feature_info(threadsafe USE_THREADS "threadsafe support")
 
 
 if(WIN32 AND EMBED_SSH_PATH)
@@ -277,7 +277,7 @@ endif()
 add_feature_info(iconv GIT_USE_ICONV "iconv encoding conversion support")
 
 
-if(THREADSAFE)
+if(USE_THREADS)
 	if(NOT WIN32)
 		find_package(Threads REQUIRED)
 	endif()

src/thread.h

@@ -12,7 +12,7 @@
 #if defined(__clang__)
 
 # if (__clang_major__ < 3 || (__clang_major__ == 3 && __clang_minor__ < 1))
-#  error Atomic primitives do not exist on this version of clang; configure libgit2 with -DTHREADSAFE=OFF
+#  error Atomic primitives do not exist on this version of clang; configure libgit2 with -DUSE_THREADS=OFF
 # else
 #  define GIT_BUILTIN_ATOMIC
 # endif
@@ -20,7 +20,7 @@
 #elif defined(__GNUC__)
 
 # if (__GNUC__ < 4 || (__GNUC__ == 4 && __GNUC_MINOR__ < 1))
-#  error Atomic primitives do not exist on this version of gcc; configure libgit2 with -DTHREADSAFE=OFF
+#  error Atomic primitives do not exist on this version of gcc; configure libgit2 with -DUSE_THREADS=OFF
 # elif (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 7))
 #  define GIT_BUILTIN_ATOMIC
 # else