Add configure option --enable-generations (enabled by default).

This option allows the user to enable or disable (with
--disable-generations or --enable-generations=no) generations in
3m. Disabling generational collection is, in most cases, a bad
idea, but it may be necessary on a platform where signal handling
doesn't work well enough to support a write barrier that is
implemented with page protection.

racket/src/cfg-racket

@@ -828,6 +828,7 @@ enable_csdefault
 enable_cgcdefault
 enable_sgc
 enable_sgcdebug
+enable_generations
 enable_backtrace
 enable_cify
 enable_pthread
@@ -1487,6 +1488,7 @@ Optional Features:
   --enable-cgcdefault     use CGC as default build (NOT RECOMMENDED)
   --enable-sgc            use Senora GC instead of Boehm GC (enabled by default)
   --enable-sgcdebug       use Senora GC for debugging (expensive; CGC only)
+  --enable-generations    3m: support generational GC (enabled by default)
   --enable-backtrace      3m: support GC backtrace dumps (expensive debug mode)
   --enable-cify           compile startup code to C instead of bytecode
   --enable-pthread        link with pthreads (usually auto-enabled if needed)
@@ -2802,6 +2804,13 @@ if test "${enable_sgcdebug+set}" = set; then :
   enableval=$enable_sgcdebug;
 fi
 
+# Check whether --enable-generations was given.
+if test "${enable_generations+set}" = set; then :
+  enableval=$enable_generations;
+else
+  enable_generations=yes
+fi
+
 # Check whether --enable-backtrace was given.
 if test "${enable_backtrace+set}" = set; then :
   enableval=$enable_backtrace;
@@ -3204,6 +3213,7 @@ show_explicitly_disabled "${enable_futures}" Futures
 
 show_explicitly_disabled "${enable_sgc}" SGC
 show_explicitly_enabled "${enable_sgcdebug}" "SGC debug mode"
+show_explicitly_disabled "${enable_generations}" "3m generational GC"
 show_explicitly_enabled "${enable_backtrace}" "3m GC backtraces" "Note that this mode is not intended for normal Racket use"
 show_explicitly_enabled "${enable_cify}" "Startup compiled to C"
 show_explicitly_disabled "${enable_cify}" "Startup compiled to C"
@@ -5061,6 +5071,16 @@ if test "${enable_sgc}" = "yes" ; then
   OPTIONS="$OPTIONS -DUSE_SENORA_GC"
 fi
 
+if test "${enable_generations}" = "yes" ; then
+
+$as_echo "#define USE_GC_GENS 1" >>confdefs.h
+
+else
+
+$as_echo "#define USE_GC_GENS 0" >>confdefs.h
+
+fi
+
 ############## Strip tool ################
 
 if test "${enable_strip}" = "" ; then

racket/src/racket/configure.ac

@@ -60,9 +60,10 @@ AC_ARG_ENABLE(csdefault,  [  --enable-csdefault      use CS as default build])
 AC_ARG_ENABLE(cgcdefault, [  --enable-cgcdefault     use CGC as default build (NOT RECOMMENDED)])
 AC_ARG_ENABLE(sgc,     [  --enable-sgc            use Senora GC instead of Boehm GC (enabled by default)], , enable_sgc=yes)
 AC_ARG_ENABLE(sgcdebug,[  --enable-sgcdebug       use Senora GC for debugging (expensive; CGC only)])
-AC_ARG_ENABLE(backtrace, [  --enable-backtrace      3m: support GC backtrace dumps (expensive debug mode)])
+AC_ARG_ENABLE(generations,[  --enable-generations    3m: support generational GC (enabled by default)], , enable_generations=yes)
+AC_ARG_ENABLE(backtrace,  [  --enable-backtrace      3m: support GC backtrace dumps (expensive debug mode)])
 
-AC_ARG_ENABLE(cify, [  --enable-cify           compile startup code to C instead of bytecode])
+AC_ARG_ENABLE(cify,       [  --enable-cify           compile startup code to C instead of bytecode])
 
 AC_ARG_ENABLE(pthread, [  --enable-pthread        link with pthreads (usually auto-enabled if needed)])
 AC_ARG_ENABLE(stackup, [  --enable-stackup        assume "up" if stack direction cannot be determined])
@@ -204,6 +205,7 @@ show_explicitly_disabled "${enable_futures}" Futures
 
 show_explicitly_disabled "${enable_sgc}" SGC
 show_explicitly_enabled "${enable_sgcdebug}" "SGC debug mode"
+show_explicitly_disabled "${enable_generations}" "3m generational GC"
 show_explicitly_enabled "${enable_backtrace}" "3m GC backtraces" "Note that this mode is not intended for normal Racket use"
 show_explicitly_enabled "${enable_cify}" "Startup compiled to C"
 show_explicitly_disabled "${enable_cify}" "Startup compiled to C"
@@ -787,6 +789,12 @@ if test "${enable_sgc}" = "yes" ; then
   OPTIONS="$OPTIONS -DUSE_SENORA_GC"
 fi
 
+if test "${enable_generations}" = "yes" ; then
+  AC_DEFINE(USE_GC_GENS, 1,[GC Generations])
+else
+  AC_DEFINE(USE_GC_GENS, 0,[GC Generations])
+fi
+
 ############## Strip tool ################
 
 m4_include(../ac/strip.m4)

racket/src/racket/gc2/newgc.c

@@ -768,8 +768,9 @@ static void NewGC_initialize(NewGC *newgc, NewGC *inheritgc, NewGC *parentgc) {
 #endif
 
   newgc->mmu = mmu_create(newgc);
-  
-  newgc->generations_available = 1;
+
+  newgc->generations_available = USE_GC_GENS;
+
   newgc->last_full_mem_use = INITIAL_FULL_MEMORY_USE;
   newgc->new_btc_mark = 1;
 

racket/src/racket/gc2/sighand.c

@@ -12,6 +12,8 @@
 /*                      platform-specific handlers                            */
 /******************************************************************************/
 
+#ifdef USE_GC_GENS
+
 /* ========== Linux signal handler ========== */
 #if defined(linux)
 #include <signal.h>
@@ -205,6 +207,8 @@ void fault_handler(int sn, siginfo_t *si, void *ctx)
 }
 #endif
 
+#endif
+
 /******************************************************************************/
 /*                             init function                                  */
 /******************************************************************************/

racket/src/racket/mzconfig.h.in

@@ -92,4 +92,7 @@ typedef unsigned long uintptr_t;
 /* Library subpath */
 #undef SPLS_SUFFIX
 
+/* Use Generations with the GC */
+#undef USE_GC_GENS
+
 #endif

racket/src/worksp/mzconfig.h

@@ -46,4 +46,7 @@
 /* Enable single-precision floats: */
 #define USE_SINGLE_FLOATS
 
+/* Always enable generations in GC */
+#define USE_GC_GENS 1
+
 #endif