Allow emscripten platform to build without threads

CMakeLists.txt

@@ -2711,10 +2711,14 @@ endif()
 
 # We always need to have threads and timers around
 if(NOT HAVE_SDL_THREADS)
-  message_error("Threads are needed by many SDL subsystems and may not be disabled")
-  #set(SDL_THREADS_DISABLED 1)
-  #file(GLOB THREADS_SOURCES ${SDL2_SOURCE_DIR}/src/thread/generic/*.c)
-  #list(APPEND SOURCE_FILES ${THREADS_SOURCES})
+  # The emscripten platform has been carefully vetted to work without threads
+  if (EMSCRIPTEN)
+    set(SDL_THREADS_DISABLED 1)
+    file(GLOB THREADS_SOURCES ${SDL2_SOURCE_DIR}/src/thread/generic/*.c)
+    list(APPEND SOURCE_FILES ${THREADS_SOURCES})
+  else()
+    message_error("Threads are needed by many SDL subsystems and may not be disabled")
+  endif()
 endif()
 if(NOT HAVE_SDL_TIMERS)
   set(SDL_TIMER_DUMMY 1)

configure

@@ -852,7 +852,6 @@ enable_hidapi
 enable_sensor
 enable_power
 enable_filesystem
-enable_threads
 enable_timers
 enable_file
 enable_misc
@@ -1643,7 +1642,6 @@ Optional Features:
   --enable-sensor         Enable the sensor subsystem [default=yes]
   --enable-power          Enable the power subsystem [default=yes]
   --enable-filesystem     Enable the filesystem subsystem [default=yes]
-  --enable-threads        Enable the threading subsystem [default=yes]
   --enable-timers         Enable the timer subsystem [default=yes]
   --enable-file           Enable the file subsystem [default=yes]
   --enable-misc           Enable the misc subsystem [default=yes]
@@ -20351,14 +20349,11 @@ printf "%s\n" "#define SDL_FILESYSTEM_DISABLED 1" >>confdefs.h
 else
     SUMMARY_modules="${SUMMARY_modules} filesystem"
 fi
-# Check whether --enable-threads was given.
-if test ${enable_threads+y}
-then :
-  enableval=$enable_threads;
-else $as_nop
-  enable_threads=yes
-fi
-
+# Many subsystems depend on threads, so leave them enabled by default
+#AC_ARG_ENABLE(threads,
+#[AS_HELP_STRING([--enable-threads], [Enable the threading subsystem [default=yes]])],
+#              , enable_threads=yes)
+enable_threads=yes
 if test x$enable_threads != xyes; then
 
 printf "%s\n" "#define SDL_THREADS_DISABLED 1" >>confdefs.h

configure.ac

@@ -526,11 +526,12 @@ fi
 #AC_ARG_ENABLE(threads,
 #[AS_HELP_STRING([--enable-threads], [Enable the threading subsystem [default=yes]])],
 #              , enable_threads=yes)
-#if test x$enable_threads != xyes; then
-#    AC_DEFINE(SDL_THREADS_DISABLED, 1, [ ])
-#else
-#    SUMMARY_modules="${SUMMARY_modules} threads"
-#fi
+enable_threads=yes
+if test x$enable_threads != xyes; then
+    AC_DEFINE(SDL_THREADS_DISABLED, 1, [ ])
+else
+    SUMMARY_modules="${SUMMARY_modules} threads"
+fi
 AC_ARG_ENABLE(timers,
 [AS_HELP_STRING([--enable-timers], [Enable the timer subsystem [default=yes]])],
               , enable_timers=yes)