diff --git a/Makefile b/Makefile
index 1d6ae44..ed85639 100644
--- a/Makefile
+++ b/Makefile
@@ -6,7 +6,7 @@ AR=			ar
 DFLAGS=		-DHAVE_PTHREAD $(WRAP_MALLOC)
 LOBJS=		utils.o kthread.o kstring.o ksw.o bwt.o bntseq.o bwa.o bwamem.o bwamem_pair.o bwamem_extra.o malloc_wrap.o
 AOBJS=		QSufSort.o bwt_gen.o bwashm.o bwase.o bwaseqio.o bwtgap.o bwtaln.o bamlite.o \
-			is.o bwtindex.o bwape.o kopen.o pemerge.o \
+			is.o bwtindex.o bwape.o kopen.o pemerge.o maxk.o \
 			bwtsw2_core.o bwtsw2_main.o bwtsw2_aux.o bwt_lite.o \
 			bwtsw2_chain.o fastmap.o bwtsw2_pair.o
 PROG=		bwa
@@ -45,7 +45,8 @@ depend:
 QSufSort.o: QSufSort.h
 bamlite.o: bamlite.h malloc_wrap.h
 bntseq.o: bntseq.h utils.h kseq.h malloc_wrap.h khash.h
-bwa.o: bntseq.h bwa.h bwt.h ksw.h utils.h kstring.h malloc_wrap.h kseq.h
+bwa.o: bntseq.h bwa.h bwt.h ksw.h utils.h kstring.h malloc_wrap.h kvec.h
+bwa.o: kseq.h
 bwamem.o: kstring.h malloc_wrap.h bwamem.h bwt.h bntseq.h bwa.h ksw.h kvec.h
 bwamem.o: ksort.h utils.h kbtree.h
 bwamem_extra.o: bwa.h bntseq.h bwt.h bwamem.h kstring.h malloc_wrap.h
@@ -79,5 +80,6 @@ kstring.o: kstring.h malloc_wrap.h
 ksw.o: ksw.h malloc_wrap.h
 main.o: kstring.h malloc_wrap.h utils.h
 malloc_wrap.o: malloc_wrap.h
+maxk.o: bwa.h bntseq.h bwt.h bwamem.h kseq.h malloc_wrap.h
 pemerge.o: ksw.h kseq.h malloc_wrap.h kstring.h bwa.h bntseq.h bwt.h utils.h
 utils.o: utils.h ksort.h malloc_wrap.h kseq.h
diff --git a/kthread.c b/kthread.c
index 80f84cb..97359c0 100644
--- a/kthread.c
+++ b/kthread.c
@@ -67,13 +67,15 @@ struct ktp_t;
 
 typedef struct {
 	struct ktp_t *pl;
-	int step, running;
+	int64_t index;
+	int step;
 	void *data;
 } ktp_worker_t;
 
 typedef struct ktp_t {
 	void *shared;
 	void *(*func)(void*, int, void*);
+	int64_t index;
 	int n_workers, n_steps;
 	ktp_worker_t *workers;
 	pthread_mutex_t mutex;
@@ -92,13 +94,12 @@ static void *ktp_worker(void *data)
 			// test whether another worker is doing the same step
 			for (i = 0; i < p->n_workers; ++i) {
 				if (w == &p->workers[i]) continue; // ignore itself
-				if (p->workers[i].running && p->workers[i].step == w->step)
+				if (p->workers[i].step <= w->step && p->workers[i].index < w->index)
 					break;
 			}
-			if (i == p->n_workers) break; // no other workers doing w->step; then this worker will
+			if (i == p->n_workers) break; // no workers with smaller indices are doing w->step or the previous steps
 			pthread_cond_wait(&p->cv, &p->mutex);
 		}
-		w->running = 1;
 		pthread_mutex_unlock(&p->mutex);
 
 		// working on w->step
@@ -107,7 +108,7 @@ static void *ktp_worker(void *data)
 		// update step and let other workers know
 		pthread_mutex_lock(&p->mutex);
 		w->step = w->step == p->n_steps - 1 || w->data? (w->step + 1) % p->n_steps : p->n_steps;
-		w->running = 0;
+		if (w->step == 0) w->index = p->index++;
 		pthread_cond_broadcast(&p->cv);
 		pthread_mutex_unlock(&p->mutex);
 	}
@@ -125,13 +126,15 @@ void kt_pipeline(int n_threads, void *(*func)(void*, int, void*), void *shared_d
 	aux.n_steps = n_steps;
 	aux.func = func;
 	aux.shared = shared_data;
+	aux.index = 0;
 	pthread_mutex_init(&aux.mutex, 0);
 	pthread_cond_init(&aux.cv, 0);
 
 	aux.workers = alloca(n_threads * sizeof(ktp_worker_t));
 	for (i = 0; i < n_threads; ++i) {
 		ktp_worker_t *w = &aux.workers[i];
-		w->step = w->running = 0; w->pl = &aux; w->data = 0;
+		w->step = 0; w->pl = &aux; w->data = 0;
+		w->index = aux.index++;
 	}
 
 	tid = alloca(n_threads * sizeof(pthread_t));
diff --git a/main.c b/main.c
index 9f776d4..cdac445 100644
--- a/main.c
+++ b/main.c
@@ -4,7 +4,7 @@
 #include "utils.h"
 
 #ifndef PACKAGE_VERSION
-#define PACKAGE_VERSION "0.7.12-r1039"
+#define PACKAGE_VERSION "0.7.12-r1044"
 #endif
 
 int bwa_fa2pac(int argc, char *argv[]);
@@ -25,6 +25,7 @@ int main_mem(int argc, char *argv[]);
 int main_shm(int argc, char *argv[]);
 
 int main_pemerge(int argc, char *argv[]);
+int main_maxk(int argc, char *argv[]);
 	
 static int usage()
 {
@@ -84,6 +85,7 @@ int main(int argc, char *argv[])
 	else if (strcmp(argv[1], "mem") == 0) ret = main_mem(argc-1, argv+1);
 	else if (strcmp(argv[1], "shm") == 0) ret = main_shm(argc-1, argv+1);
 	else if (strcmp(argv[1], "pemerge") == 0) ret = main_pemerge(argc-1, argv+1);
+	else if (strcmp(argv[1], "maxk") == 0) ret = main_maxk(argc-1, argv+1);
 	else {
 		fprintf(stderr, "[main] unrecognized command '%s'\n", argv[1]);
 		return 1;
diff --git a/maxk.c b/maxk.c
new file mode 100644
index 0000000..24b9d54
--- /dev/null
+++ b/maxk.c
@@ -0,0 +1,66 @@
+#include <zlib.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <limits.h>
+#include <string.h>
+#include "bwa.h"
+#include "bwamem.h"
+#include "kseq.h"
+KSEQ_DECLARE(gzFile)
+
+int main_maxk(int argc, char *argv[])
+{
+	int i, c, self = 0, max_len = 0;
+	uint8_t *cnt = 0;
+	uint64_t hist[256];
+	bwt_t *bwt;
+	kseq_t *ks;
+	smem_i *itr;
+	gzFile fp;
+
+	while ((c = getopt(argc, argv, "s")) >= 0) {
+		if (c == 's') self = 1;
+	}
+	if (optind + 2 > argc) {
+		fprintf(stderr, "Usage: bwa maxk [-s] <index.prefix> <seq.fa>\n");
+		return 1;
+	}
+	fp = strcmp(argv[optind+1], "-")? gzopen(argv[optind+1], "rb") : gzdopen(fileno(stdin), "rb");
+	ks = kseq_init(fp);
+	bwt = bwt_restore_bwt(argv[optind]);
+	itr = smem_itr_init(bwt);
+	if (self) smem_config(itr, 2, INT_MAX, 0);
+	memset(hist, 0, 8 * 256);
+
+	while (kseq_read(ks) >= 0) {
+		const bwtintv_v *a;
+		if (ks->seq.l > max_len) {
+			max_len = ks->seq.l;
+			kroundup32(max_len);
+			cnt = realloc(cnt, max_len);
+		}
+		memset(cnt, 0, ks->seq.l);
+		for (i = 0; i < ks->seq.l; ++i)
+			ks->seq.s[i] = nst_nt4_table[(int)ks->seq.s[i]];
+		smem_set_query(itr, ks->seq.l, (uint8_t*)ks->seq.s);
+		while ((a = smem_next(itr)) != 0) {
+			for (i = 0; i < a->n; ++i) {
+				bwtintv_t *p = &a->a[i];
+				int j, l, start = p->info>>32, end = (uint32_t)p->info;
+				l = end - start < 255? end - start : 255;
+				for (j = start; j < end; ++j)
+					cnt[j] = cnt[j] > l? cnt[j] : l;
+			}
+		}
+		for (i = 0; i < ks->seq.l; ++i) ++hist[cnt[i]];
+	}
+	for (i = 0; i < 256; ++i)
+		printf("%d\t%lld\n", i, (long long)hist[i]);
+	free(cnt);
+
+	smem_itr_destroy(itr);
+	bwt_destroy(bwt);
+	kseq_destroy(ks);
+	gzclose(fp);
+	return 0;
+}