diff --git a/oclengine.c b/oclengine.c
index 4557e2c..c649003 100644
--- a/oclengine.c
+++ b/oclengine.c
@@ -1571,7 +1571,6 @@ vg_ocl_prefix_check(vg_ocl_context_t *vocp, int slot)
 			       found_delta, orig_delta);
 			res = 1;
 		}
-		vocp->voc_pattern_rewrite = 1;
 	} else {
 		vxcp->vxc_delta += (vocp->voc_ocl_cols * vocp->voc_ocl_rows);
 	}
@@ -1879,6 +1878,7 @@ vg_opencl_loop(void *arg)
 	vg_ocl_context_t *vocp = (vg_ocl_context_t *) arg;
 	int i;
 	int round, nrows, ncols;
+	int pattern_generation;
 
 	const BN_ULONG rekey_max = 100000000;
 	BN_ULONG npoints, rekey_at;
@@ -1991,6 +1991,10 @@ l_rekey:
 	    !vocp->voc_rekey_func(vocp))
 		goto enomem;
 
+	vg_exec_context_upgrade_lock(vxcp);
+
+	pattern_generation = vcp->vc_pattern_generation;
+
 	/* Generate a new random private key */
 	EC_KEY_generate_key(pkey);
 	npoints = 0;
@@ -2007,6 +2011,8 @@ l_rekey:
 
 	EC_POINT_copy(ppbase[0], EC_KEY_get0_public_key(pkey));
 
+	vg_exec_context_downgrade_lock(vxcp);
+
 	if (vcp->vc_pubkey_base) {
 		EC_POINT_add(pgroup,
 			     ppbase[0],
@@ -2076,6 +2082,15 @@ l_rekey:
 					vg_output_timing(vcp, c, &tvstart);
 				c = 0;
 			}
+			vg_exec_context_yield(vxcp);
+
+			/* If the patterns changed, reload it to the GPU */
+			if (vocp->voc_rekey_func &&
+			    (pattern_generation !=
+			     vcp->vc_pattern_generation)) {
+				vocp->voc_pattern_rewrite = 1;
+				rekey_at = 0;
+			}
 		}
 
 		if (vcp->vc_halt)
@@ -2176,6 +2191,8 @@ l_rekey:
 			printf("done!\n");
 	}
 
+	vg_exec_context_yield(vxcp);
+
 	if (ppbase) {
 		for (i = 0; i < (nrows + ncols); i++)
 			if (ppbase[i])
diff --git a/pattern.c b/pattern.c
index 012ec21..3bc1a8f 100644
--- a/pattern.c
+++ b/pattern.c
@@ -45,9 +45,106 @@ vg_exec_context_new_key(void)
 	return EC_KEY_new_by_curve_name(NID_secp256k1);
 }
 
+/*
+ * Thread synchronization helpers
+ */
+
+static pthread_mutex_t vg_thread_lock = PTHREAD_MUTEX_INITIALIZER;
+static pthread_cond_t vg_thread_rdcond = PTHREAD_COND_INITIALIZER;
+static pthread_cond_t vg_thread_wrcond = PTHREAD_COND_INITIALIZER;
+static pthread_cond_t vg_thread_upcond = PTHREAD_COND_INITIALIZER;
+static vg_exec_context_t *vg_threads = NULL;
+static int vg_thread_excl = 0;
+
+static void
+__vg_exec_context_yield(vg_exec_context_t *vxcp)
+{
+	vxcp->vxc_lockmode = 0;
+	while (vg_thread_excl) {
+		if (vxcp->vxc_stop) {
+			assert(vg_thread_excl);
+			vxcp->vxc_stop = 0;
+			pthread_cond_signal(&vg_thread_upcond);
+		}
+		pthread_cond_wait(&vg_thread_rdcond, &vg_thread_lock);
+	}
+	assert(!vxcp->vxc_stop);
+	assert(!vxcp->vxc_lockmode);
+	vxcp->vxc_lockmode = 1;
+}
+
+int
+vg_exec_context_upgrade_lock(vg_exec_context_t *vxcp)
+{
+	vg_exec_context_t *tp;
+
+	if (vxcp->vxc_lockmode == 2)
+		return 0;
+
+	pthread_mutex_lock(&vg_thread_lock);
+
+	assert(vxcp->vxc_lockmode == 1);
+	vxcp->vxc_lockmode = 0;
+
+	if (vg_thread_excl++) {
+		assert(vxcp->vxc_stop);
+		vxcp->vxc_stop = 0;
+		pthread_cond_signal(&vg_thread_upcond);
+		pthread_cond_wait(&vg_thread_wrcond, &vg_thread_lock);
+
+		for (tp = vg_threads; tp != NULL; tp = tp->vxc_next) {
+			assert(!tp->vxc_lockmode);
+			assert(!tp->vxc_stop);
+		}
+
+	} else {
+		for (tp = vg_threads; tp != NULL; tp = tp->vxc_next) {
+			if (tp->vxc_lockmode) {
+				assert(tp->vxc_lockmode != 2);
+				tp->vxc_stop = 1;
+			}
+		}
+
+		do {
+			for (tp = vg_threads; tp != NULL; tp = tp->vxc_next) {
+				if (tp->vxc_lockmode) {
+					assert(tp->vxc_lockmode != 2);
+					pthread_cond_wait(&vg_thread_upcond,
+							  &vg_thread_lock);
+					break;
+				}
+			}
+		} while (tp);
+	}
+
+	vxcp->vxc_lockmode = 2;
+	pthread_mutex_unlock(&vg_thread_lock);
+	return 1;
+}
+
+void
+vg_exec_context_downgrade_lock(vg_exec_context_t *vxcp)
+{
+	pthread_mutex_lock(&vg_thread_lock);
+
+	assert(vxcp->vxc_lockmode == 2);
+	assert(!vxcp->vxc_stop);
+	if (!--vg_thread_excl) {
+		vxcp->vxc_lockmode = 1;
+		pthread_cond_broadcast(&vg_thread_rdcond);
+		pthread_mutex_unlock(&vg_thread_lock);
+		return;
+	}
+	pthread_cond_signal(&vg_thread_wrcond);
+	__vg_exec_context_yield(vxcp);
+	pthread_mutex_unlock(&vg_thread_lock);
+}
+
 int
 vg_exec_context_init(vg_context_t *vcp, vg_exec_context_t *vxcp)
 {
+	pthread_mutex_lock(&vg_thread_lock);
+
 	memset(vxcp, 0, sizeof(*vxcp));
 
 	vxcp->vxc_vc = vcp;
@@ -64,18 +161,62 @@ vg_exec_context_init(vg_context_t *vcp, vg_exec_context_t *vxcp)
 	vxcp->vxc_key = vg_exec_context_new_key();
 	assert(vxcp->vxc_key);
 	EC_KEY_precompute_mult(vxcp->vxc_key, vxcp->vxc_bnctx);
+
+	vxcp->vxc_lockmode = 0;
+	vxcp->vxc_stop = 0;
+
+	vxcp->vxc_next = vg_threads;
+	vg_threads = vxcp;
+	__vg_exec_context_yield(vxcp);
+	pthread_mutex_unlock(&vg_thread_lock);
 	return 1;
 }
 
 void
 vg_exec_context_del(vg_exec_context_t *vxcp)
 {
+	vg_exec_context_t *tp, **pprev;
+
+	if (vxcp->vxc_lockmode == 2)
+		vg_exec_context_downgrade_lock(vxcp);
+
+	pthread_mutex_lock(&vg_thread_lock);
+	assert(vxcp->vxc_lockmode == 1);
+	vxcp->vxc_lockmode = 0;
+
+	for (pprev = &vg_threads, tp = *pprev;
+	     (tp != vxcp) && (tp != NULL);
+	     pprev = &tp->vxc_next, tp = *pprev);
+
+	assert(tp == vxcp);
+	*pprev = tp->vxc_next;
+
+	if (tp->vxc_stop)
+		pthread_cond_signal(&vg_thread_upcond);
+
 	BN_clear_free(&vxcp->vxc_bntarg);
 	BN_clear_free(&vxcp->vxc_bnbase);
 	BN_clear_free(&vxcp->vxc_bntmp);
 	BN_clear_free(&vxcp->vxc_bntmp2);
 	BN_CTX_free(vxcp->vxc_bnctx);
 	vxcp->vxc_bnctx = NULL;
+	pthread_mutex_unlock(&vg_thread_lock);
+}
+
+void
+vg_exec_context_yield(vg_exec_context_t *vxcp)
+{
+	if (vxcp->vxc_lockmode == 2)
+		vg_exec_context_downgrade_lock(vxcp);
+
+	else if (vxcp->vxc_stop) {
+		assert(vxcp->vxc_lockmode == 1);
+		pthread_mutex_lock(&vg_thread_lock);
+		__vg_exec_context_yield(vxcp);
+		pthread_mutex_unlock(&vg_thread_lock);
+	}
+
+	assert(vxcp->vxc_lockmode == 1);
 }
 
 void
@@ -473,6 +614,7 @@ int
 vg_context_add_patterns(vg_context_t *vcp,
 			const char ** const patterns, int npatterns)
 {
+	vcp->vc_pattern_generation++;
 	return vcp->vc_add_patterns(vcp, patterns, npatterns);
 }
 
@@ -480,6 +622,7 @@ void
 vg_context_clear_all_patterns(vg_context_t *vcp)
 {
 	vcp->vc_clear_all_patterns(vcp);
+	vcp->vc_pattern_generation++;
 }
 
 int
@@ -1690,7 +1833,7 @@ vg_prefix_test(vg_exec_context_t *vxcp)
 research:
 	vp = vg_prefix_avl_search(&vcpp->vcp_avlroot, &vxcp->vxc_bntarg);
 	if (vp) {
-		if (vg_exec_upgrade_lock(vxcp))
+		if (vg_exec_context_upgrade_lock(vxcp))
 			goto research;
 
 		vg_exec_context_consolidate_key(vxcp);
@@ -1717,6 +1860,7 @@ research:
 					vcpp, &vxcp->vxc_bntmp,
 					&vxcp->vxc_bntmp2,
 					vxcp->vxc_bnctx);
+			vcpp->base.vc_pattern_generation++;
 		}
 		res = 1;
 	}
@@ -1983,7 +2127,7 @@ restart_loop:
 
 		re = vcrp->vcr_regex[i];
 
-		if (vg_exec_upgrade_lock(vxcp) &&
+		if (vg_exec_context_upgrade_lock(vxcp) &&
 		    ((i >= vcrp->base.vc_npatterns) ||
 		     (vcrp->vcr_regex[i] != re)))
 			goto restart_loop;
@@ -2008,6 +2152,7 @@ restart_loop:
 				vcrp->vcr_regex_extra[nres];
 			vcrp->vcr_regex_pat[i] = vcrp->vcr_regex_pat[nres];
 			vcrp->base.vc_npatterns = nres;
+			vcrp->base.vc_pattern_generation++;
 		}
 		res = 1;
 	}
diff --git a/pattern.h b/pattern.h
index 48682bc..95fbfae 100644
--- a/pattern.h
+++ b/pattern.h
@@ -33,7 +33,7 @@
 #include <unistd.h>
 #endif
 
-#define VANITYGEN_VERSION "0.19"
+#define VANITYGEN_VERSION "0.20pre"
 
 
 typedef struct _vg_context_s vg_context_t;
@@ -49,6 +49,11 @@ typedef struct _vg_exec_context_s {
 	BIGNUM				vxc_bnbase;
 	BIGNUM				vxc_bntmp;
 	BIGNUM				vxc_bntmp2;
+
+	/* Thread synchronization */
+	struct _vg_exec_context_s	*vxc_next;
+	int				vxc_lockmode;
+	int				vxc_stop;
 } vg_exec_context_t;
 
 /* Init/cleanup for common execution context */
@@ -58,9 +63,10 @@ extern void vg_exec_context_consolidate_key(vg_exec_context_t *vxcp);
 extern void vg_exec_context_calc_address(vg_exec_context_t *vxcp);
 extern EC_KEY *vg_exec_context_new_key(void);
 
-/* Implementation-specific lock/unlock/consolidate */
-extern void vg_exec_downgrade_lock(vg_exec_context_t *vxcp);
-extern int vg_exec_upgrade_lock(vg_exec_context_t *vxcp);
+/* Execution context lock handling functions */
+extern void vg_exec_context_downgrade_lock(vg_exec_context_t *vxcp);
+extern int vg_exec_context_upgrade_lock(vg_exec_context_t *vxcp);
+extern void vg_exec_context_yield(vg_exec_context_t *vxcp);
 
 
 typedef void (*vg_free_func_t)(vg_context_t *);
@@ -89,6 +95,7 @@ struct _vg_context_s {
 	unsigned long		vc_npatterns;
 	unsigned long		vc_npatterns_start;
 	unsigned long long	vc_found;
+	int			vc_pattern_generation;
 	double			vc_chance;
 	const char		*vc_result_file;
 	const char		*vc_key_protect_pass;
diff --git a/vanitygen.c b/vanitygen.c
index 48b4b7d..a47e3fc 100644
--- a/vanitygen.c
+++ b/vanitygen.c
@@ -34,169 +34,6 @@
 
 const char *version = VANITYGEN_VERSION;
 
-typedef struct _vg_thread_context_s {
-	vg_exec_context_t		base;
-	struct _vg_thread_context_s	*vt_next;
-	int				vt_mode;
-	int				vt_stop;
-} vg_thread_context_t;
-
-
-/*
- * To synchronize pattern lists, we use a special shared-exclusive lock
- * geared toward being held in shared mode 99.9% of the time.
- */
-
-static pthread_mutex_t vg_thread_lock = PTHREAD_MUTEX_INITIALIZER;
-static pthread_cond_t vg_thread_rdcond = PTHREAD_COND_INITIALIZER;
-static pthread_cond_t vg_thread_wrcond = PTHREAD_COND_INITIALIZER;
-static pthread_cond_t vg_thread_upcond = PTHREAD_COND_INITIALIZER;
-static vg_thread_context_t *vg_threads = NULL;
-static int vg_thread_excl = 0;
-
-void
-__vg_thread_yield(vg_thread_context_t *vtcp)
-{
-	vtcp->vt_mode = 0;
-	while (vg_thread_excl) {
-		if (vtcp->vt_stop) {
-			assert(vg_thread_excl);
-			vtcp->vt_stop = 0;
-			pthread_cond_signal(&vg_thread_upcond);
-		}
-		pthread_cond_wait(&vg_thread_rdcond, &vg_thread_lock);
-	}
-	assert(!vtcp->vt_stop);
-	assert(!vtcp->vt_mode);
-	vtcp->vt_mode = 1;
-}
-
-void
-vg_thread_context_init(vg_context_t *vcp, vg_thread_context_t *vtcp)
-{
-	vtcp->vt_mode = 0;
-	vtcp->vt_stop = 0;
-
-	pthread_mutex_lock(&vg_thread_lock);
-	vg_exec_context_init(vcp, &vtcp->base);
-	vtcp->vt_next = vg_threads;
-	vg_threads = vtcp;
-	__vg_thread_yield(vtcp);
-	pthread_mutex_unlock(&vg_thread_lock);
-}
-
-void
-vg_thread_context_del(vg_thread_context_t *vtcp)
-{
-	vg_thread_context_t *tp, **pprev;
-
-	if (vtcp->vt_mode == 2)
-		vg_exec_downgrade_lock(&vtcp->base);
-
-	pthread_mutex_lock(&vg_thread_lock);
-	assert(vtcp->vt_mode == 1);
-	vtcp->vt_mode = 0;
-
-	for (pprev = &vg_threads, tp = *pprev;
-	     (tp != vtcp) && (tp != NULL);
-	     pprev = &tp->vt_next, tp = *pprev);
-
-	assert(tp == vtcp);
-	*pprev = tp->vt_next;
-
-	if (tp->vt_stop)
-		pthread_cond_signal(&vg_thread_upcond);
-
-	vg_exec_context_del(&vtcp->base);
-	pthread_mutex_unlock(&vg_thread_lock);
-}
-
-void
-vg_thread_yield(vg_thread_context_t *vtcp)
-{
-	if (vtcp->vt_mode == 2)
-		vg_exec_downgrade_lock(&vtcp->base);
-
-	else if (vtcp->vt_stop) {
-		assert(vtcp->vt_mode == 1);
-		pthread_mutex_lock(&vg_thread_lock);
-		__vg_thread_yield(vtcp);
-		pthread_mutex_unlock(&vg_thread_lock);
-	}
-
-	assert(vtcp->vt_mode == 1);
-}
-
-
-
-void
-vg_exec_downgrade_lock(vg_exec_context_t *vxcp)
-{
-	vg_thread_context_t *vtcp = (vg_thread_context_t *) vxcp;
-	pthread_mutex_lock(&vg_thread_lock);
-
-	assert(vtcp->vt_mode == 2);
-	assert(!vtcp->vt_stop);
-	if (!--vg_thread_excl) {
-		vtcp->vt_mode = 1;
-		pthread_cond_broadcast(&vg_thread_rdcond);
-		pthread_mutex_unlock(&vg_thread_lock);
-		return;
-	}
-	pthread_cond_signal(&vg_thread_wrcond);
-	__vg_thread_yield(vtcp);
-	pthread_mutex_unlock(&vg_thread_lock);
-}
-
-int
-vg_exec_upgrade_lock(vg_exec_context_t *vxcp)
-{
-	vg_thread_context_t *vtcp = (vg_thread_context_t *) vxcp;
-	vg_thread_context_t *tp;
-
-	if (vtcp->vt_mode == 2)
-		return 0;
-
-	pthread_mutex_lock(&vg_thread_lock);
-
-	assert(vtcp->vt_mode == 1);
-	vtcp->vt_mode = 0;
-
-	if (vg_thread_excl++) {
-		assert(vtcp->vt_stop);
-		vtcp->vt_stop = 0;
-		pthread_cond_signal(&vg_thread_upcond);
-		pthread_cond_wait(&vg_thread_wrcond, &vg_thread_lock);
-
-		for (tp = vg_threads; tp != NULL; tp = tp->vt_next) {
-			assert(!tp->vt_mode);
-			assert(!tp->vt_stop);
-		}
-
-	} else {
-		for (tp = vg_threads; tp != NULL; tp = tp->vt_next) {
-			if (tp->vt_mode) {
-				assert(tp->vt_mode != 2);
-				tp->vt_stop = 1;
-			}
-		}
-
-		do {
-			for (tp = vg_threads; tp != NULL; tp = tp->vt_next) {
-				if (tp->vt_mode) {
-					assert(tp->vt_mode != 2);
-					pthread_cond_wait(&vg_thread_upcond,
-							  &vg_thread_lock);
-					break;
-				}
-			}
-		} while (tp);
-	}
-
-	vtcp->vt_mode = 2;
-	pthread_mutex_unlock(&vg_thread_lock);
-	return 1;
-}
 
 /*
  * Address search thread main loop
@@ -224,16 +61,16 @@ vg_thread_loop(void *arg)
 	EC_POINT *pbatchinc;
 
 	vg_test_func_t test_func = vcp->vc_test;
-	vg_thread_context_t ctx;
+	vg_exec_context_t ctx;
 	vg_exec_context_t *vxcp;
 
 	struct timeval tvstart;
 
 
 	memset(&ctx, 0, sizeof(ctx));
-	vxcp = &ctx.base;
+	vxcp = &ctx;
 
-	vg_thread_context_init(vcp, &ctx);
+	vg_exec_context_init(vcp, &ctx);
 
 	pkey = vxcp->vxc_key;
 	pgroup = EC_KEY_get0_group(pkey);
@@ -282,7 +119,7 @@ vg_thread_loop(void *arg)
 
 	while (!vcp->vc_halt) {
 		if (++npoints >= rekey_at) {
-			pthread_mutex_lock(&vg_thread_lock);
+			vg_exec_context_upgrade_lock(vxcp);
 			/* Generate a new random private key */
 			EC_KEY_generate_key(pkey);
 			npoints = 0;
@@ -299,7 +136,7 @@ vg_thread_loop(void *arg)
 			assert(rekey_at > 0);
 
 			EC_POINT_copy(ppnt[0], EC_KEY_get0_public_key(pkey));
-			pthread_mutex_unlock(&vg_thread_lock);
+			vg_exec_context_downgrade_lock(vxcp);
 
 			npoints++;
 			vxcp->vxc_delta = 0;
@@ -387,11 +224,11 @@ vg_thread_loop(void *arg)
 			c = 0;
 		}
 
-		vg_thread_yield(&ctx);
+		vg_exec_context_yield(vxcp);
 	}
 
 out:
-	vg_thread_context_del(&ctx);
+	vg_exec_context_del(&ctx);
 	vg_context_thread_exit(vcp);
 
 	for (i = 0; i < ptarraysize; i++)