racketcgc: use SenoraGC instead of Boehm GC by default

This new default for Unix and Mac OS X trades performance for
portability (hopefully), but for most users the switch affects only
for the build process, where `racketcgc` is used to build `racket`.

To continue using Boehm GC, configure with `--disable-sgc`.

For now, Boehm GC continues to be the default for Windows.

racket/src/README

@@ -29,9 +29,7 @@ To compile with MinGW tools, follow the Unix instructions below; do not
 use `--enable-shared', because DLLs will be generated automatically.
 The result is a Windows-style build, but without MzCOM. If you are using
 a variant of MinGW without "libdelayimp.a", get the implementation of
-"delayimp.c" from MinGW-w64 and compile it to "libdelayimp.a". When
+"delayimp.c" from MinGW-w64 and compile it to "libdelayimp.a".
-compiling with MinGW-w64 for 64-bit mode, the `--enable-sgc' flag
-to `configure' is currently required.
 
 To compile with Cygwin tools, follow the Unix instructions below, and be
 sure to configure with `--enable-shared'.  The result is a Unix-style
@@ -286,17 +284,6 @@ Cross-compilation requires at least two flags to `configure':
    This flag is needed because building and installing Racket requires
    running (an intermediate version of) Racket.
 
-A third `configure' flag is typical:
-
- * `--enable-sgc', which uses a simpler garbage collector for the
-   intermediate variant of Racket that is normally used only to build
-   the final variant (see CGC vs 3m below).
-
-   Otherwise, you may need to set CC_FOR_BUILD to a compiler for the
-   build platform, so that helper executables can be created in the
-   process of building the intermediate Racket that is used to build
-   the final Racket.
-
 Some less commonly needed `configure' flags:
 
  * `--enable-stackup', if the target platform's stack grows up.
@@ -312,7 +299,6 @@ the NDK, use (all on one line)
 
   configure --host=arm-linux-androideabi 
             --enable-sysroot="[ndk]/platforms/android-[N]/arch-arm"
-            --enable-sgc
             --enable-racket=racket
 
 where [ndk] is the path to the installed NDK, [N] is a target version
@@ -385,33 +371,29 @@ documentation for "config search paths" for more information.
 ========================================================================
 
 At a minimum, to port Racket to a new platform, edit "racket/sconfig.h"
-to provide a platform-specific compilation information.  As distributed,
+to provide a platform-specific compilation information.
-"racket/sconfig.h" contains configurations for the following platforms:
-
-              Windows (x86, x86_64)
-              Mac OS X (PPC, x86, x86_64)
-              Linux (x86, x86_64, PPC, 68k)
-              Cygwin (x86)
-              Solaris (x86, Sparc)
-              FreeBSD (x86, x86_64)
-              OpenBSD (x86)
-              NetBSD (x86)
-
-If your platform is not supported by the Boehm garbage collector
-(distributed with Racket source), provide the `--enable-sgc' flag to
-`configure'.
 
 ========================================================================
  Additional Compilation Notes
 ========================================================================
 
-Garbage Collector
+CGC Build Options
 -----------------
 
-The conservative garbage collector distributed with Racket (in the "gc"
+As noted above in "CGC versus 3m", Racket builds a CGC variant in the
-directory) has been modified slightly from Boehm's standard
+process of creating the normal 3m variant. Within the CGC variant, two
-distribution.  Mostly, the change modify the way that object
+implementations are possible.
-finalization is handled.
+
+By default, Racket CGC is implemented with SenoraGC (in the "sgc"
+directory), which is relativey portable. Provide `--disable-sgc` to
+instead use the Boehm GC (in the "gc" directory), which should perform
+better and was the default for Racket CGC through version 6.1.
+
+The variant of the Boehm GC that is included with Racket has been
+modified slightly from Boehm's standard distribution; mostly, the
+changes modify the way that object finalization is handled.
+
+[Currently, the Windows build still uses the Boehm GC by default.]
 
 Floating point, x87, SSE, Extflonums, and the JIT
 -------------------------------------------------

racket/src/configure

@@ -1456,8 +1456,8 @@ Optional Features:
   --enable-macprefix      allow --prefix with a Mac OS X install
   --enable-mac64          allow 64-bit Mac OS X build (enabled by default)
   --enable-cgcdefault     use CGC as default build (NOT RECOMMENDED)
-  --enable-sgc            use Senora GC instead of the Boehm GC
+  --enable-sgc            use Senora GC instead of the Boehm GC (enabled by default)
-  --enable-sgcdebug       use Senora GC for debugging
+  --enable-sgcdebug       use Senora GC for debugging (expensive debug mode)
   --enable-backtrace      3m: support GC backtrace dumps (expensive debug mode)
   --enable-pthread        link with pthreads (usually auto-enabled if needed)
   --enable-stackup        assume "up" if stack direction cannot be determined
@@ -2738,6 +2738,8 @@ fi
 # Check whether --enable-sgc was given.
 if test "${enable_sgc+set}" = set; then :
   enableval=$enable_sgc;
+else
+  enable_sgc=yes
 fi
 
 # Check whether --enable-sgcdebug was given.
@@ -3007,7 +3009,7 @@ show_explicitly_disabled "${enable_places}" Places
 show_explicitly_enabled "${enable_futures}" Futures
 show_explicitly_disabled "${enable_futures}" Futures
 
-show_explicitly_enabled "${enable_sgc}" SGC
+show_explicitly_disabled "${enable_sgc}" SGC
 show_explicitly_enabled "${enable_sgcdebug}" "SGC debug mode"
 show_explicitly_enabled "${enable_backtrace}" "3m GC backtraces" "Note that this mode is not intended for normal Racket use"
 
@@ -5496,8 +5498,8 @@ $as_echo_n "checking $msg... " >&6; }
      #include <fcntl.h>
      int main() {
       void *p;
-      p = mmap(0, 2 << 16, PROT_READ | PROT_WRITE | PROT_EXEC, MAP_PRIVATE, open("/dev/zero", O_RDWR), 0);
+      p = mmap(0, 2 << 16, PROT_READ | PROT_WRITE, MAP_PRIVATE, open("/dev/zero", O_RDWR), 0);
-      mprotect(p, 2 << 16, PROT_READ | PROT_WRITE | PROT_EXEC);
+      mprotect(p, 2 << 16, PROT_READ | PROT_WRITE);
       return 0;
      }
 _ACEOF
@@ -5515,6 +5517,36 @@ $as_echo "$use_mprotect" >&6; }
 $as_echo "#define HAVE_MMAP_MPROTECT 1" >>confdefs.h
 
   fi
+
+  if test "${use_mprotect}" = "yes" && test "${enable_sgc}" != "yes" ; then
+     msg="mprotect with PROT_EXEC"
+    { $as_echo "$as_me:${as_lineno-$LINENO}: checking $msg" >&5
+$as_echo_n "checking $msg... " >&6; }
+    cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+       #include <sys/mman.h>
+       #include <fcntl.h>
+       int main() {
+        void *p;
+        p = mmap(0, 2 << 16, PROT_READ | PROT_WRITE, MAP_PRIVATE, open("/dev/zero", O_RDWR), 0);
+        if (mprotect(p, 2 << 16, PROT_READ | PROT_WRITE | PROT_EXEC)) return 1;
+        return 0;
+       }
+_ACEOF
+if ac_fn_c_try_link "$LINENO"; then :
+  can_mprotect_exec=yes
+else
+  can_mprotect_exec=no
+fi
+rm -f core conftest.err conftest.$ac_objext \
+    conftest$ac_exeext conftest.$ac_ext
+    { $as_echo "$as_me:${as_lineno-$LINENO}: result: $can_mprotect_exec" >&5
+$as_echo "$can_mprotect_exec" >&6; }
+    if test "${can_mprotect_exec}" = "no" ; then
+      echo "Senora GC is required due to mprotect() failure"
+    fi
+  fi
 fi
 
 if test "${check_page_size}" = "yes" ; then

racket/src/racket/configure.ac

@@ -66,8 +66,8 @@ AC_ARG_ENABLE(macprefix, [  --enable-macprefix      allow --prefix with a Mac OS
 AC_ARG_ENABLE(mac64,   [  --enable-mac64          allow 64-bit Mac OS X build (enabled by default)], , enable_mac64=yes)
 
 AC_ARG_ENABLE(cgcdefault, [  --enable-cgcdefault     use CGC as default build (NOT RECOMMENDED)])
-AC_ARG_ENABLE(sgc,     [  --enable-sgc            use Senora GC instead of the Boehm GC])
+AC_ARG_ENABLE(sgc,     [  --enable-sgc            use Senora GC instead of the Boehm GC (enabled by default)], , enable_sgc=yes)
-AC_ARG_ENABLE(sgcdebug,[  --enable-sgcdebug       use Senora GC for debugging])
+AC_ARG_ENABLE(sgcdebug,[  --enable-sgcdebug       use Senora GC for debugging (expensive debug mode)])
 AC_ARG_ENABLE(backtrace, [  --enable-backtrace      3m: support GC backtrace dumps (expensive debug mode)])
 
 AC_ARG_ENABLE(pthread, [  --enable-pthread        link with pthreads (usually auto-enabled if needed)])
@@ -298,7 +298,7 @@ show_explicitly_disabled "${enable_places}" Places
 show_explicitly_enabled "${enable_futures}" Futures
 show_explicitly_disabled "${enable_futures}" Futures
 
-show_explicitly_enabled "${enable_sgc}" SGC
+show_explicitly_disabled "${enable_sgc}" SGC
 show_explicitly_enabled "${enable_sgcdebug}" "SGC debug mode"
 show_explicitly_enabled "${enable_backtrace}" "3m GC backtraces" "Note that this mode is not intended for normal Racket use"
 
@@ -1104,14 +1104,32 @@ if test "${check_for_mprotect}" = "yes" ; then
      #include <fcntl.h>
      int main() {
       void *p;
-      p = mmap(0, 2 << 16, PROT_READ | PROT_WRITE | PROT_EXEC, MAP_PRIVATE, open("/dev/zero", O_RDWR), 0);
+      p = mmap(0, 2 << 16, PROT_READ | PROT_WRITE, MAP_PRIVATE, open("/dev/zero", O_RDWR), 0);
-      mprotect(p, 2 << 16, PROT_READ | PROT_WRITE | PROT_EXEC);
+      mprotect(p, 2 << 16, PROT_READ | PROT_WRITE);
       return 0;
      }])], use_mprotect=yes, use_mprotect=no)
   AC_MSG_RESULT($use_mprotect)
   if test "${use_mprotect}" = "yes" ; then
      AC_DEFINE(HAVE_MMAP_MPROTECT,1,[Have mmap and mprotect])
   fi
+
+  if test "${use_mprotect}" = "yes" && test "${enable_sgc}" != "yes" ; then
+    [ msg="mprotect with PROT_EXEC" ]
+    AC_MSG_CHECKING($msg)
+    AC_LINK_IFELSE([AC_LANG_SOURCE([
+       #include <sys/mman.h>
+       #include <fcntl.h>
+       int main() {
+        void *p;
+        p = mmap(0, 2 << 16, PROT_READ | PROT_WRITE, MAP_PRIVATE, open("/dev/zero", O_RDWR), 0);
+        if (mprotect(p, 2 << 16, PROT_READ | PROT_WRITE | PROT_EXEC)) return 1;
+        return 0;
+       }])], can_mprotect_exec=yes, can_mprotect_exec=no)
+    AC_MSG_RESULT($can_mprotect_exec)
+    if test "${can_mprotect_exec}" = "no" ; then
+      echo "Senora GC is required due to mprotect() failure"
+    fi
+  fi
 fi
 
 if test "${check_page_size}" = "yes" ; then

racket/src/racket/sgc/README

@@ -1,17 +1,15 @@
 SenoraGC is a relatively portable conservative GC for a slightly
-cooperative environment.
+cooperative environment. Its API is based on the Boehm GC.
 
-The collector is intended mainly for debugging and memory tracing, but
+The collector was originally intended for debugging and memory
-it can also act as a reasonbaly efficient, general-purpose,
+tracing, but it can also act as a reasonbaly efficient,
-conservative collector. The standard Racket build uses SGC for
+general-purpose, conservative collector.
-certain platforms where Boehm's GC hasn't been ported, yet (notably,
-OSKit and BeOS).
 
-This collector is not recommended as a replacement for Boehm's GC if
+If you intend to use the CGC variant of Racket instead of the (usual)
-you can get Boehm's to work at all. SenoraGC MIGHT be useful if, for
+3m variant, then instead of SenoraGC, consider using the variant of
-some reason, Boehm's collector does not work for your platform.
+the Boehm GC that is distributed with Racket; it should perform
-SenoraGC MIGHT be useful as a debugging collector if you can figure
+significantly better. Enable the Boehm GC by providing `--disable-sgc`
-out the [undocumented] debugging utilities.
+to `configure`.
 
 Usage:
 
@@ -24,6 +22,6 @@ actually done automatically for static variables, but it can't be done
 portably in general. (See AUTO_STATIC_ROOTS_IF_POSSIBLE in the flags
 section.)
 
-GC space is allocated using malloc() and free(). Alternatively, the GC
+GC space is allocated using mmap() where available, malloc()
-can define malloc() and free() itself if platform-specific allocation
+otherwise. The GC can define malloc() and free() itself if
-routines are supported.
+platform-specific allocation routines are supported.

racket/src/racket/sgc/sgc.c

@@ -315,8 +315,9 @@
 /* SECTOR_SEGMENT_SIZE determines the alignment of collector blocks.
    Since it should be a power of 2, LOG_SECTOR_SEGMENT_SIZE is
    specified directly. A larger block size speeds up GC, but wastes
-   more unallocated bytes in same-size buckets. */
+   more unallocated bytes in same-size buckets. The block size must
-#define LOG_SECTOR_SEGMENT_SIZE 14
+   be at least as large as the OS's page size. */
+#define LOG_SECTOR_SEGMENT_SIZE 16
 #define SECTOR_SEGMENT_SIZE (1 << LOG_SECTOR_SEGMENT_SIZE)
 #define SECTOR_SEGMENT_MASK (~(SECTOR_SEGMENT_SIZE-1))
 
@@ -328,7 +329,7 @@
 
 /* Number of sector segments to be allocated at once with
    malloc() to avoid waste when obtaining the proper alignment. */
-#define SECTOR_SEGMENT_GROUP_SIZE 32
+#define SECTOR_SEGMENT_GROUP_SIZE 16
 
 /* Number of bits used in 32-bit level table for checking existence of
    a sector. Creates a table of (1 << SECTOR_LOOKUP_SHIFT) pointers
@@ -989,6 +990,10 @@ static void *ofm_malloc_zero(size_t len)
   return mmap_sector((len >> LOG_SECTOR_SEGMENT_SIZE) + 1, 0);
 }
 
+/* Instead of calling mmap()/unmap() every time we need to
+   allocate/free a sector, use the allocation-cache layer from
+   "gc2" for non-executable pages: */
+
 # define APAGE_SIZE SECTOR_SEGMENT_SIZE
 # define NO_ALLOC_CACHE_FREE
 # include "../gc2/my_qsort.c"

racket/src/racket/src/string.c

@@ -2086,9 +2086,9 @@ char *scheme_version(void)
 # define VERSION_SUFFIX ""
 #else
 # ifdef USE_SENORA_GC
-#  define VERSION_SUFFIX " [cgc~]"
-# else
 #  define VERSION_SUFFIX " [cgc]"
+# else
+#  define VERSION_SUFFIX " [cgc/b]"
 # endif
 #endif
 

racket/src/worksp/README

@@ -68,7 +68,7 @@ racket\src\README if you don't know about the two variants.)
 
 
 If you can't run "build.bat" or don't want to, you have to perform
-several steps: first builg RacketCGC, then build Racket3m, etc.
+several steps: first build RacketCGC, then build Racket3m, etc.
 
 Building RacketCGC and GRacketCGC
 ---------------------------------