yet another revision of memory limiting: the glibc mallinfo() approach has been shown to be unacceptably broken, so the fallback implementation has been improved

 * mallinfo() is not only broken on 64-bit systems but slows things
   down linearilly to the memory size of the process.
   E.g. after 500000<%A>, SciTECO will act sluggish! Shutting down
   afterwards can take minutes...
   mallinfo() was thus finally discarded as a memory measurement
   technique.
 * Evaluating /proc/self/statm? has also been evaluated and discarded
   because doing this frequently is even slower.
 * Instead, the fallback implementation has been drastically improved:
   * If possible use C++14 global sized deallocators, allowing memory measurements
     across the entire C++ code base with minimal runtime overhead.
     Since we only depend on C++11, a lengthy Autoconf check had to be introduced.
   * Use malloc_usable_size() with global non-sized deallocators to
     measure the approx. memory usage of the entire process (at least
     the ones done via C++).
     The cheaper C++11 sized deallocators implemented via SciTECO::Object still
     have precedence, so this affects Scintilla code only.
 * With both improvements the test case
   sciteco -e '<@EU[X^E\a]"^E\a"%a>'
   is handled sufficiently well now on glibc and performance is much better
   now.
 * The jemalloc-specific technique has been removed since it no longer
   brings any benefits compared to the improved fallback technique.
   Even the case of using malloc_usable_size() in strict C++ mode is
   up to 3 times faster.
 * The new fallback implementation might actually be good enough for
   Windows as well if some MSVCRT-specific support is added, like
   using _msize() instead of malloc_usable_size().
   This must be tested and benchmarked, so we keep the Windows-specific
   implementation for the time being.

1 files changed, 29 insertions, 9 deletions

diff --git a/configure.ac b/configure.ac
index e3fd728..1bd446d 100644
--- a/configure.ac
+++ b/configure.ac
@@ -172,15 +172,35 @@ case $host in
 	;;
 esac
 
-# Check for optional glibc features.
-# Will probably only be found on Linux/glibc.
-AC_CHECK_HEADERS([malloc.h])
-AC_CHECK_FUNCS([malloc_trim mallinfo])
-
-# jemalloc-specific functions.
-# Will probably only be foudn on FreeBSD.
-AC_CHECK_HEADERS([malloc_np.h])
-AC_CHECK_FUNCS([mallctlnametomib mallctlbymib])
+# Check for optional libc features.
+# Some of this will only be found on glibc,
+# others on FreeBSD/jemalloc.
+AC_CHECK_HEADERS([malloc.h malloc_np.h])
+AC_CHECK_FUNCS([malloc_trim malloc_usable_size])
+
+# Check whether compiler supports global sized deallocations.
+# If yes, this will improve the memory limiting fallback
+# implementation.
+# Once we can depend on C++14, this check is no longer necessary.
+AC_CACHE_CHECK([if C++ compiler supports -fsized-deallocation],
+               [sciteco_cv_sized_deallocation_result], [
+	AC_LANG_PUSH(C++)
+	OLD_CXXFLAGS="$CXXFLAGS"
+	CXXFLAGS="$CXXFLAGS -fsized-deallocation"
+	AC_COMPILE_IFELSE([AC_LANG_PROGRAM(
+		[[#include <new>]],
+		[[(::operator delete)(0, 256)]]
+	)], sciteco_cv_sized_deallocation_result=yes,
+	    sciteco_cv_sized_deallocation_result=no)
+	CXXFLAGS="$OLD_CXXFLAGS"
+	AC_LANG_POP(C++)
+])
+if [[ x$sciteco_cv_sized_deallocation_result = xyes ]]; then
+	AC_DEFINE(HAVE_SIZED_DEALLOCATION, 1,
+	          [C++ compiler supports -fsized-deallocation])
+fi
+AM_CONDITIONAL(HAVE_SIZED_DEALLOCATION,
+               test "$sciteco_cv_sized_deallocation_result" = yes)
 
 #
 # Config options