diff --git a/moo/kernel/Process.moo b/moo/kernel/Process.moo
index 7d1ce4f..32320d9 100644
--- a/moo/kernel/Process.moo
+++ b/moo/kernel/Process.moo
@@ -228,30 +228,27 @@ method(#class,#abstract) xxx. => method(#class) xxx { self subclassResponsibilit
 
 		## create an internal semaphore for timeout notification.
 		s := Semaphore new. 
-
-		## grant the partial membership to the internal semaphore.
-		## it's partial because it's not added to self.semarr.
-		##s _group: self. 
 		self addSemaphore: s.
 
-		## arrange the processor to notify upon timeout.
-		System signal: s after: seconds.
-
 		[ 
+			## arrange the processor to notify upon timeout.
+			System signal: s afterSecs: seconds.
+
 			## wait on the semaphore group.
 			r := self wait. 
 
 			## if the internal semaphore has been signaled, 
 			## arrange to return nil to indicate timeout.
-			if (r == s) { r := nil }
-			elsif (r signalAction notNil) { r signalAction value: r }.
+			if (r == s) { r := nil } ## timed out
+			elsif (r signalAction notNil) { r signalAction value: r }. ## run the signal action block
 		] ensure: [
+			## System<<unsignal: doesn't thrown an exception even if the semaphore s is not
+			## register with System<<signal:afterXXX:. otherwise, i would do like this line
+			## commented out.
+			## [ System unsignal: s ] ensure: [ self removeSemaphore: s ].
 
-			## nullify the membership
-			self removeSemaphore: s.
-
-			## cancel the notification arrangement in case it didn't time out.
 			System unsignal: s.
+			self removeSemaphore: s
 		].
 
 		^r.
diff --git a/moo/kernel/test-002.moo b/moo/kernel/test-002.moo
index a7cb265..a34cf5d 100644
--- a/moo/kernel/test-002.moo
+++ b/moo/kernel/test-002.moo
@@ -115,7 +115,6 @@ class MyObject(Object)
 			[ self test_mutex = #(2000 6000) ],
 			####[ self test_sem_sig ],
 
-		
 			[ System sleepForSecs: 2. self.a == 300 ] ## sleep before checking self.a to prevent different result depending on process switching frequency and speed
 		).
 
diff --git a/moo/lib/bigint.c b/moo/lib/bigint.c
index 6ffa9d2..621f4a0 100644
--- a/moo/lib/bigint.c
+++ b/moo/lib/bigint.c
@@ -56,14 +56,6 @@
 
 #include "moo-prv.h"
 
-
-#define ENABLE_KARATSUBA
-#if defined(MOO_DEBUG_BIGINT)
-#	define KARATSUBA_CUTOFF 3
-#else
-#	define KARATSUBA_CUTOFF 32
-#endif
-
 #if (MOO_LIW_BITS == MOO_OOW_BITS)
 	/* nothing special */
 #elif (MOO_LIW_BITS == MOO_OOHW_BITS)
@@ -1119,10 +1111,18 @@ static MOO_INLINE void multiply_unsigned_array (const moo_liw_t* x, moo_oow_t xs
  *  X * B^2n => X << (MOO_LIW_BITS * n * 2)
  * --------------------------------------------------------------------
  */
-#define CANNOT_KARATSUBA(xs, ys) \
+ 
+#if !defined(NDEBUG)
+#define CANNOT_KARATSUBA(moo,xs,ys) \
+	((xs) < (moo)->option.karatsuba_cutoff || (ys) < (moo)->option.karatsuba_cutoff || \
+	((xs) > (ys) && (ys) <= (((xs) + 1) / 2)) || \
+	((xs) < (ys) && (xs) <= (((ys) + 1) / 2)))
+#else
+#define CANNOT_KARATSUBA(moo,xs,ys) \
 	((xs) < KARATSUBA_CUTOFF || (ys) < KARATSUBA_CUTOFF || \
 	((xs) > (ys) && (ys) <= (((xs) + 1) / 2)) || \
 	((xs) < (ys) && (xs) <= (((ys) + 1) / 2)))
+#endif
 
 static MOO_INLINE moo_oow_t multiply_unsigned_array_karatsuba (moo_t* moo, const moo_liw_t* x, moo_oow_t xs, const moo_liw_t* y, moo_oow_t ys, moo_liw_t* z)
 {
@@ -1185,7 +1185,7 @@ static MOO_INLINE moo_oow_t multiply_unsigned_array_karatsuba (moo_t* moo, const
 
 	/* place (a0 + a1) * (b0 + b1) at the shifted position */
 	zsp = z + nshifts;
-	if (CANNOT_KARATSUBA(tmplen[0], tmplen[1]))
+	if (CANNOT_KARATSUBA(moo, tmplen[0], tmplen[1]))
 	{
 		multiply_unsigned_array (tmp[0], tmplen[0], tmp[1], tmplen[1], zsp);
 		xlen = count_effective (zsp, tmplen[0] + tmplen[1]);
@@ -1199,7 +1199,7 @@ static MOO_INLINE moo_oow_t multiply_unsigned_array_karatsuba (moo_t* moo, const
 	/* tmp[0] = a0 * b0 */
 	tmplen[0] = ndigits_xl + ndigits_yl;
 	MOO_MEMSET (tmp[0], 0, sizeof(moo_liw_t) * tmplen[0]);
-	if (CANNOT_KARATSUBA(ndigits_xl, ndigits_yl))
+	if (CANNOT_KARATSUBA(moo, ndigits_xl, ndigits_yl))
 	{
 		multiply_unsigned_array (x, ndigits_xl, y, ndigits_yl, tmp[0]);
 		tmplen[0] = count_effective(tmp[0], tmplen[0]);
@@ -1213,7 +1213,7 @@ static MOO_INLINE moo_oow_t multiply_unsigned_array_karatsuba (moo_t* moo, const
 	/* tmp[1] = a1 * b1 */
 	tmplen[1] = ndigits_xh + ndigits_yh;
 	MOO_MEMSET (tmp[1], 0, sizeof(moo_liw_t) * tmplen[1]);
-	if (CANNOT_KARATSUBA(ndigits_xh, ndigits_yh))
+	if (CANNOT_KARATSUBA(moo, ndigits_xh, ndigits_yh))
 	{
 		multiply_unsigned_array (x + nshifts, ndigits_xh, y + nshifts, ndigits_yh, tmp[1]);
 		tmplen[1] = count_effective (tmp[1], tmplen[1]);
@@ -1304,7 +1304,7 @@ oops:
 	tmplen[2] = tmplen[0] + tmplen[1]; 
 	tmp[2] = moo_callocmem (moo, MOO_SIZEOF(moo_liw_t) * tmplen[2]);
 	if (!tmp[2]) goto oops;
-	if (CANNOT_KARATSUBA(tmplen[0], tmplen[1]))
+	if (CANNOT_KARATSUBA(moo, tmplen[0], tmplen[1]))
 	{
 		multiply_unsigned_array (tmp[0], tmplen[0], tmp[1], tmplen[1], tmp[2]);
 		xlen = count_effective (tmp[2], tmplen[2]);
@@ -1318,7 +1318,7 @@ oops:
 	/* tmp[0] = a0 * b0 */
 	tmplen[0] = ndigits_xl + ndigits_yl;
 	MOO_MEMSET (tmp[0], 0, sizeof(moo_liw_t) * tmplen[0]);
-	if (CANNOT_KARATSUBA(ndigits_xl, ndigits_yl))
+	if (CANNOT_KARATSUBA(moo, ndigits_xl, ndigits_yl))
 	{
 		multiply_unsigned_array (x, ndigits_xl, y, ndigits_yl, tmp[0]);
 		tmplen[0] = count_effective(tmp[0], tmplen[0]);
@@ -1332,7 +1332,7 @@ oops:
 	/* tmp[1] = a1 * b1 */
 	tmplen[1] = ndigits_xh + ndigits_yh;
 	MOO_MEMSET (tmp[1], 0, sizeof(moo_liw_t) * tmplen[1]);
-	if (CANNOT_KARATSUBA(ndigits_xh, ndigits_yh))
+	if (CANNOT_KARATSUBA(moo, ndigits_xh, ndigits_yh))
 	{
 		multiply_unsigned_array (x + nshifts, ndigits_xh, y + nshifts, ndigits_yh, tmp[1]);
 		tmplen[1] = count_effective (tmp[1], tmplen[1]);
@@ -1561,7 +1561,7 @@ static moo_oop_t multiply_unsigned_integers (moo_t* moo, moo_oop_t x, moo_oop_t
 	if (!z) return MOO_NULL;
 
 #if defined(ENABLE_KARATSUBA)
-	if (CANNOT_KARATSUBA (xs, ys))
+	if (CANNOT_KARATSUBA(moo,xs, ys))
 	{
 #endif
 		multiply_unsigned_array (
diff --git a/moo/lib/exec.c b/moo/lib/exec.c
index a423763..5e4ede5 100644
--- a/moo/lib/exec.c
+++ b/moo/lib/exec.c
@@ -2492,16 +2492,14 @@ static moo_pfrc_t pf_system_remove_semaphore (moo_t* moo, moo_ooi_t nargs)
 		moo->sem_gcfin = (moo_oop_semaphore_t)moo->_nil;
 	}
 
-	if (MOO_OOP_IS_SMOOI(sem->heap_index) && 
-	    sem->heap_index != MOO_SMOOI_TO_OOP(-1))
+	if (MOO_OOP_IS_SMOOI(sem->heap_index) && sem->heap_index != MOO_SMOOI_TO_OOP(-1))
 	{
 		/* the semaphore is in the timed semaphore heap */
 		delete_from_sem_heap (moo, MOO_OOP_TO_SMOOI(sem->heap_index));
 		MOO_ASSERT (moo, sem->heap_index == MOO_SMOOI_TO_OOP(-1));
 	}
 
-	if (MOO_OOP_IS_SMOOI(sem->io_index) &&
-	    sem->io_index != MOO_SMOOI_TO_OOP(-1))
+	if (MOO_OOP_IS_SMOOI(sem->io_index) && sem->io_index != MOO_SMOOI_TO_OOP(-1))
 	{
 		/* the semaphore is associated with IO */
 		if (delete_from_sem_io (moo, MOO_OOP_TO_SMOOI(sem->io_index)) <= -1)
diff --git a/moo/lib/main.c b/moo/lib/main.c
index ad59777..fea10f3 100644
--- a/moo/lib/main.c
+++ b/moo/lib/main.c
@@ -2117,6 +2117,37 @@ static int handle_logopt (moo_t* moo, const moo_bch_t* str)
 	return 0;
 }
 
+#if !defined(NDEBUG)
+static int handle_dbgopt (moo_t* moo, const moo_bch_t* str)
+{
+	xtn_t* xtn = moo_getxtn (moo);
+	const moo_bch_t* cm, * flt;
+	moo_oow_t len;
+	unsigned int trait, dbgopt = 0;
+
+	cm = str - 1;
+	do
+	{
+		flt = cm + 1;
+
+		cm = moo_findbcharinbcstr(flt, ',');
+		len = cm? (cm - flt): moo_countbcstr(flt);
+		if (moo_compbcharsbcstr (flt, len, "gc") == 0)  dbgopt |= MOO_DEBUG_GC;
+		else if (moo_compbcharsbcstr (flt, len, "bigint") == 0)  dbgopt |= MOO_DEBUG_BIGINT;
+		/* TODO: error handling for unknown options */
+	}
+	while (cm);
+
+	moo_getoption (moo, MOO_TRAIT, &trait);
+	trait |= dbgopt;
+	moo_setoption (moo, MOO_TRAIT, &trait);
+	return 0;
+}
+#endif
+
+
+#define MIN_MEMSIZE 2048000ul
+
 int main (int argc, char* argv[])
 {
 	static moo_ooch_t str_my_object[] = { 'M', 'y', 'O', 'b','j','e','c','t' }; /*TODO: make this an argument */
@@ -2132,16 +2163,25 @@ int main (int argc, char* argv[])
 	moo_bci_t c;
 	static moo_bopt_lng_t lopt[] =
 	{
-		{ ":log",    'l' },
-		{ MOO_NULL, '\0' }
+		{ ":log",     'l' },
+		{ ":memsize", 'm' },
+#if !defined(NDEBUG)
+		{ ":debug",   '\0' }, /* NOTE: there is no short option for --debug */
+#endif
+		{ MOO_NULL,   '\0' }
 	};
 	static moo_bopt_t opt =
 	{
-		"l:",
+		"l:m:",
 		lopt
 	};
 
 	const char* logopt = MOO_NULL;
+	moo_oow_t memsize = MIN_MEMSIZE;
+
+#if !defined(NDEBUG)
+	const char* dbgopt = MOO_NULL;
+#endif
 
 	setlocale (LC_ALL, "");
 
@@ -2161,6 +2201,19 @@ int main (int argc, char* argv[])
 				logopt = opt.arg;
 				break;
 
+			case 'm':
+				memsize = strtoul(opt.arg, MOO_NULL, 0);
+				if (memsize <= MIN_MEMSIZE) memsize = MIN_MEMSIZE;
+				break;
+
+			case '\0':
+				if (moo_compbcstr(opt.lngopt, "debug") == 0)
+				{
+					dbgopt = opt.arg;
+					break;
+				}
+				goto print_usage;
+
 			case ':':
 				if (opt.lngopt)
 					fprintf (stderr, "bad argument for '%s'\n", opt.lngopt);
@@ -2195,7 +2248,7 @@ int main (int argc, char* argv[])
 	lt_dlinit ();
 #endif
 
-	moo = moo_open (&sys_mmgr, MOO_SIZEOF(xtn_t), 2048000lu, &vmprim, MOO_NULL);
+	moo = moo_open (&sys_mmgr, MOO_SIZEOF(xtn_t), memsize, &vmprim, MOO_NULL);
 	if (!moo)
 	{
 		fprintf (stderr, "ERROR: cannot open moo\n");
@@ -2242,6 +2295,17 @@ int main (int argc, char* argv[])
 		xtn->logmask = MOO_LOG_ALL_TYPES | MOO_LOG_ERROR | MOO_LOG_FATAL;
 	}
 
+#if !defined(NDEBUG)
+	if (dbgopt)
+	{
+		if (handle_dbgopt (moo, dbgopt) <= -1)
+		{
+			close_moo (moo);
+			return -1;
+		}
+	}
+#endif
+
 	if (moo_ignite(moo) <= -1)
 	{
 		moo_logbfmt (moo, MOO_LOG_ERROR | MOO_LOG_STDERR, "ERROR: cannot ignite moo - [%d] %js\n", moo_geterrnum(moo), moo_geterrstr(moo));
diff --git a/moo/lib/moo-opt.h b/moo/lib/moo-opt.h
index 490e46d..478c7a3 100644
--- a/moo/lib/moo-opt.h
+++ b/moo/lib/moo-opt.h
@@ -47,7 +47,7 @@ struct moo_uopt_t
 {
 	/* input */
 	const moo_uch_t* str; /* option string  */
-	moo_uopt_lng_t*    lng; /* long options */
+	moo_uopt_lng_t*  lng; /* long options */
 
 	/* output */
 	moo_uci_t        opt; /* character checked for validity */
@@ -57,10 +57,10 @@ struct moo_uopt_t
 	const moo_uch_t* lngopt; 
 
 	/* input + output */
-	int               ind; /* index into parent argv vector */
+	int              ind; /* index into parent argv vector */
 
 	/* input + output - internal*/
-	moo_uch_t*        cur;
+	moo_uch_t*       cur;
 };
 
 
@@ -78,7 +78,7 @@ struct moo_bopt_t
 {
 	/* input */
 	const moo_bch_t* str; /* option string  */
-	moo_bopt_lng_t*    lng; /* long options */
+	moo_bopt_lng_t*  lng; /* long options */
 
 	/* output */
 	moo_bci_t        opt; /* character checked for validity */
@@ -88,10 +88,10 @@ struct moo_bopt_t
 	const moo_bch_t* lngopt; 
 
 	/* input + output */
-	int               ind; /* index into parent argv vector */
+	int              ind; /* index into parent argv vector */
 
 	/* input + output - internal*/
-	moo_bch_t*        cur;
+	moo_bch_t*       cur;
 };
 
 #if defined(__cplusplus)
diff --git a/moo/lib/moo-prv.h b/moo/lib/moo-prv.h
index 96585db..04d63ce 100644
--- a/moo/lib/moo-prv.h
+++ b/moo/lib/moo-prv.h
@@ -44,9 +44,12 @@
  * PUSH_CONTEXT, PUSH_INTLIT, PUSH_INTLIT, SEND_BLOCK_COPY */
 #define MOO_USE_MAKE_BLOCK
 
+/* define this to enable karatsuba multiplication in bigint */
+#define MOO_ENABLE_KARATSUBA
+#define MOO_KARATSUBA_CUTOFF 32
+#define MOO_KARATSUBA_CUTOFF_DEBUG 3
+
 #if !defined(NDEBUG)
-/* this is for gc debugging */
-#define MOO_DEBUG_GC 1
 /*#define MOO_DEBUG_LEXER 1*/
 #define MOO_DEBUG_COMPILER 1
 #define MOO_DEBUG_VM_PROCESSOR 1
@@ -55,6 +58,9 @@
 #define MOO_PROFILE_VM 1
 #endif
 
+
+
+
 /* allow the caller to drive process switching by calling
  * moo_switchprocess(). */
 #define MOO_EXTERNAL_PROCESS_SWITCH
diff --git a/moo/lib/moo.c b/moo/lib/moo.c
index 5485855..1689ebd 100644
--- a/moo/lib/moo.c
+++ b/moo/lib/moo.c
@@ -96,6 +96,9 @@ int moo_init (moo_t* moo, moo_mmgr_t* mmgr, moo_oow_t heapsz, const moo_vmprim_t
 	moo->option.dfl_symtab_size = MOO_DFL_SYMTAB_SIZE;
 	moo->option.dfl_sysdic_size = MOO_DFL_SYSDIC_SIZE;
 	moo->option.dfl_procstk_size = MOO_DFL_PROCSTK_SIZE;
+#if !defined(NDEBUG)
+	moo->option.karatsuba_cutoff = MOO_KARATSUBA_CUTOFF;
+#endif
 
 	moo->log.capa = MOO_ALIGN_POW2(1, MOO_LOG_CAPA_ALIGN); /* TODO: is this a good initial size? */
 	/* alloate the log buffer in advance though it may get reallocated
@@ -244,6 +247,9 @@ int moo_setoption (moo_t* moo, moo_option_t id, const void* value)
 	{
 		case MOO_TRAIT:
 			moo->option.trait = *(const unsigned int*)value;
+		#if !defined(NDEBUG)
+			moo->option.karatsuba_cutoff = ((moo->option.trait & MOO_DEBUG_BIGINT)? MOO_KARATSUBA_CUTOFF_DEBUG: MOO_KARATSUBA_CUTOFF);
+		#endif
 			return 0;
 
 		case MOO_LOG_MASK:
diff --git a/moo/lib/moo.h b/moo/lib/moo.h
index 878bab0..313f161 100644
--- a/moo/lib/moo.h
+++ b/moo/lib/moo.h
@@ -113,12 +113,17 @@ typedef enum moo_option_dflval_t moo_option_dflval_t;
 
 enum moo_trait_t
 {
+#if !defined(NDEBUG)
+	MOO_DEBUG_GC     = (1 << 0),
+	MOO_DEBUG_BIGINT = (1 << 1),
+#endif
+
 	/* perform no garbage collection when the heap is full. 
 	 * you still can use moo_gc() explicitly. */
-	MOO_NOGC = (1 << 0),
+	MOO_NOGC = (1 << 8),
 
 	/* wait for running process when exiting from the main method */
-	MOO_AWAIT_PROCS = (1 << 1)
+	MOO_AWAIT_PROCS = (1 << 9)
 };
 typedef enum moo_trait_t moo_trait_t;
 
@@ -1130,6 +1135,11 @@ struct moo_t
 		moo_oow_t dfl_symtab_size;
 		moo_oow_t dfl_sysdic_size;
 		moo_oow_t dfl_procstk_size; 
+
+#if !defined(NDEBUG)
+		/* set automatically when trait is set */
+		int karatsuba_cutoff;
+#endif
 	} option;
 
 	moo_vmprim_t vmprim;
diff --git a/moo/lib/obj.c b/moo/lib/obj.c
index 3b5f13f..e8e59fe 100644
--- a/moo/lib/obj.c
+++ b/moo/lib/obj.c
@@ -30,8 +30,8 @@ void* moo_allocbytes (moo_t* moo, moo_oow_t size)
 {
 	moo_uint8_t* ptr;
 
-#if defined(MOO_DEBUG_GC)
-	if (!(moo->option.trait & MOO_NOGC)) moo_gc (moo);
+#if !defined(NDEBUG)
+	if ((moo->option.trait &MOO_DEBUG_GC) && !(moo->option.trait & MOO_NOGC)) moo_gc (moo);
 #endif
 
 	ptr = moo_allocheapmem (moo, moo->curheap, size);
diff --git a/moo/lib/opt-impl.h b/moo/lib/opt-impl.h
index a2d050c..19e2d1b 100644
--- a/moo/lib/opt-impl.h
+++ b/moo/lib/opt-impl.h
@@ -1,9 +1,3 @@
-
-/* this file is supposed to be included by opt.c multiple times */
-
-
-
-
 /*
  * $Id$
  *
@@ -30,6 +24,10 @@
     THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
+
+/* this file is supposed to be included by opt.c multiple times */
+
+
 #include "moo-opt.h"
 #include "moo-utl.h"