diff --git a/xwords4/common/device.c b/xwords4/common/device.c
index 7ed8316eb..de753bed1 100644
--- a/xwords4/common/device.c
+++ b/xwords4/common/device.c
@@ -575,7 +575,7 @@ static void
 setAckSendTimerLocked( XW_DUtilCtxt* dutil, XWEnv xwe, DevCtxt* dc )
 {
     if ( 0 == dc->ackTimer.key ) {
-        XP_U32 inWhenMS = 10 * 1000;
+        XP_U32 inWhenMS = 7500;
         dc->ackTimer.key = tmr_set( dutil, xwe, inWhenMS, onAckSendTimer,
                                     dutil );
         XP_ASSERT( 0 != dc->ackTimer.key );
diff --git a/xwords4/common/dictmgr.c b/xwords4/common/dictmgr.c
index 3b184e65d..bfc0b7d42 100644
--- a/xwords4/common/dictmgr.c
+++ b/xwords4/common/dictmgr.c
@@ -22,6 +22,7 @@
 #include "dictnry.h"
 #include "strutils.h"
 #include "dictmgr.h"
+#include "xwmutex.h"
 
 #ifdef CPLUS
 extern "C" {
@@ -44,7 +45,7 @@ typedef struct _DictPair {
 
 struct DictMgrCtxt {
     DictPair pairs[DMGR_MAX_DICTS];
-    pthread_mutex_t mutex;
+    MutexState mutex;
     MPSLOT
 };
 
@@ -63,7 +64,7 @@ DictMgrCtxt*
 dmgr_make( MPFORMAL_NOCOMMA )
 {
     DictMgrCtxt* dmgr = XP_CALLOC( mpool, sizeof(*dmgr) );
-    pthread_mutex_init( &dmgr->mutex, NULL );
+    mtx_init( &dmgr->mutex, XP_FALSE );
     MPASSIGN( dmgr->mpool, mpool );
     return dmgr;
 }
@@ -77,7 +78,7 @@ dmgr_destroy( DictMgrCtxt* dmgr, XWEnv xwe )
         dict_unref( pair->dict, xwe );
         XP_FREEP( dmgr->mpool, &pair->key );
     }
-    pthread_mutex_destroy( &dmgr->mutex );
+    mtx_destroy( &dmgr->mutex );
     XP_FREE( dmgr->mpool, dmgr );
 }
 
@@ -86,7 +87,7 @@ dmgr_get( DictMgrCtxt* dmgr, XWEnv xwe, const XP_UCHAR* key )
 {
     const DictionaryCtxt* result = NULL;
 
-    pthread_mutex_lock( &dmgr->mutex );
+    WITH_MUTEX( &dmgr->mutex );
 
     XP_S16 index = findFor( dmgr, key );
     if ( 0 <= index ) {
@@ -96,14 +97,14 @@ dmgr_get( DictMgrCtxt* dmgr, XWEnv xwe, const XP_UCHAR* key )
 
     XP_LOGFF( "(key=%s)=>%p", key, result );
     printInOrder( dmgr );
-    pthread_mutex_unlock( &dmgr->mutex );
+    END_WITH_MUTEX();
     return result;
 }
 
 void
 dmgr_put( DictMgrCtxt* dmgr, XWEnv xwe, const XP_UCHAR* key, const DictionaryCtxt* dict )
 {
-    pthread_mutex_lock( &dmgr->mutex );
+    WITH_MUTEX( &dmgr->mutex );
 
     XP_S16 loc = findFor( dmgr, key );
     if ( NOT_FOUND == loc ) { /* reuse the last one */
@@ -118,7 +119,7 @@ dmgr_put( DictMgrCtxt* dmgr, XWEnv xwe, const XP_UCHAR* key, const DictionaryCtx
     XP_LOGFF( "(key=%s, dict=%p)", key, dict );
     printInOrder( dmgr );
 
-    pthread_mutex_unlock( &dmgr->mutex );
+    END_WITH_MUTEX();
 }
 
 static XP_S16
diff --git a/xwords4/common/dictnry.c b/xwords4/common/dictnry.c
index 8720dce91..be27a9ccd 100644
--- a/xwords4/common/dictnry.c
+++ b/xwords4/common/dictnry.c
@@ -31,6 +31,7 @@
 #include "dictiter.h"
 #include "game.h"
 #include "dbgutil.h"
+#include "xwmutex.h"
 
 #ifdef CPLUS
 extern "C" {
@@ -52,13 +53,13 @@ p_dict_ref( const DictionaryCtxt* dict, XWEnv XP_UNUSED(xwe)
 {
     if ( !!dict ) {
         DictionaryCtxt* _dict = (DictionaryCtxt*)dict;
-        pthread_mutex_lock( &_dict->mutex );
+        WITH_MUTEX( &_dict->mutex );
         ++_dict->refCount;
 #ifdef DEBUG_REF
         XP_LOGFF( "(dict=%p): refCount now %d (from line %d of %s() in %s)",
                  dict, dict->refCount, line, func, file );
 #endif
-        pthread_mutex_unlock( &_dict->mutex );
+        END_WITH_MUTEX();
     }
     return dict;
 }
@@ -72,7 +73,7 @@ p_dict_unref( const DictionaryCtxt* dict, XWEnv xwe
 {
     if ( !!dict ) {
         DictionaryCtxt* _dict = (DictionaryCtxt*)dict;
-        pthread_mutex_lock( &_dict->mutex );
+        WITH_MUTEX( &_dict->mutex );
         XP_ASSERT( 0 != _dict->refCount );
         --_dict->refCount;
         XP_ASSERT( 0 <= _dict->refCount );
@@ -80,11 +81,11 @@ p_dict_unref( const DictionaryCtxt* dict, XWEnv xwe
         XP_LOGFF( "(dict=%p): refCount now %d  (from line %d of %s() in %s)",
                   dict, dict->refCount, line, func, file );
 #endif
-        pthread_mutex_unlock( &_dict->mutex );
+        END_WITH_MUTEX();
         if ( 0 == _dict->refCount ) {
             /* There's a race here. If another thread locks the mutex we'll
                still destroy the dict (and the locked mutex!!!) PENDING */
-            pthread_mutex_destroy( &_dict->mutex );
+            mtx_destroy( &_dict->mutex );
             (*dict->destructor)( _dict, xwe );
         }
     }
@@ -1208,7 +1209,7 @@ dict_super_init( MPFORMAL DictionaryCtxt* dict )
     dict->func_dict_edge_with_tile = dict_super_edge_with_tile;
     dict->func_dict_getShortName = dict_getName;
 
-    pthread_mutex_init( &dict->mutex, NULL );
+    mtx_init( &dict->mutex, XP_FALSE );
 } /* dict_super_init */
 
 void
diff --git a/xwords4/common/dictnry.h b/xwords4/common/dictnry.h
index 80a4ea2f8..086546855 100644
--- a/xwords4/common/dictnry.h
+++ b/xwords4/common/dictnry.h
@@ -32,6 +32,7 @@
 #include "dawg.h"
 #include "model.h"
 #include "mempool.h"
+#include "xwmutex.h"
 
 #ifdef CPLUS
 extern "C" {
@@ -74,7 +75,7 @@ struct DictionaryCtxt {
                                              array_edge* from, Tile tile );
     const XP_UCHAR* (*func_dict_getShortName)( const DictionaryCtxt* dict );
 
-    pthread_mutex_t mutex;
+    MutexState mutex;
 
     array_edge* topEdge;
     array_edge* base; /* the physical beginning of the dictionary; not
diff --git a/xwords4/common/dutil.c b/xwords4/common/dutil.c
index 0ba7ede9b..cd255fb67 100644
--- a/xwords4/common/dutil.c
+++ b/xwords4/common/dutil.c
@@ -59,7 +59,7 @@ void
 dutil_super_init( MPFORMAL XW_DUtilCtxt* dutil )
 {
 #ifdef XWFEATURE_KNOWNPLAYERS
-    pthread_mutex_init( &dutil->kpMutex, NULL );
+    mtx_init( &dutil->kpMutex, XP_FALSE );
 #endif
 
     MPASSIGN( dutil->mpool, mpool );
diff --git a/xwords4/common/dutil.h b/xwords4/common/dutil.h
index a9dad67ac..87471b9d3 100644
--- a/xwords4/common/dutil.h
+++ b/xwords4/common/dutil.h
@@ -28,6 +28,7 @@
 #include "vtabmgr.h"
 #include "commstyp.h"
 #include "nlityp.h"
+#include "xwmutex.h"
 #include "cJSON.h"
 
 typedef enum { UNPAUSED,
@@ -120,7 +121,7 @@ struct XW_DUtilCtxt {
     void* timersState;          /* owned by timers.c */
 #ifdef XWFEATURE_KNOWNPLAYERS   /* owned by knownplyr.c */
     void* kpCtxt;
-    pthread_mutex_t kpMutex;
+    MutexState kpMutex;
 #endif
     VTableMgr* vtMgr;
 #ifdef DEBUG
diff --git a/xwords4/common/knownplyr.c b/xwords4/common/knownplyr.c
index 060c88955..f46d55069 100644
--- a/xwords4/common/knownplyr.c
+++ b/xwords4/common/knownplyr.c
@@ -61,11 +61,9 @@ loadFromStream( XW_DUtilCtxt* dutil, KPState* state, XWStreamCtxt* stream )
 }
 
 static KPState*
-loadState( XW_DUtilCtxt* dutil, XWEnv xwe )
+loadStateLocked( XW_DUtilCtxt* dutil, XWEnv xwe )
 {
     // LOG_FUNC();
-    pthread_mutex_lock( &dutil->kpMutex );
-
     KPState* state = (KPState*)dutil->kpCtxt;
     if ( NULL == state ) {
         dutil->kpCtxt = state = XP_CALLOC( dutil->mpool, sizeof(*state) );
@@ -116,13 +114,11 @@ saveState( XW_DUtilCtxt* dutil, XWEnv xwe, KPState* state )
 }
 
 static void
-releaseState( XW_DUtilCtxt* dutil, XWEnv xwe, KPState* state )
+releaseStateLocked( XW_DUtilCtxt* dutil, XWEnv xwe, KPState* state )
 {
     XP_ASSERT( state->inUse );
     saveState( dutil, xwe, state );
     state->inUse = XP_FALSE;
-
-    pthread_mutex_unlock( &dutil->kpMutex );
 }
 
 static void
@@ -249,9 +245,11 @@ kplr_addAddr( XW_DUtilCtxt* dutil, XWEnv xwe, const CommsAddrRec* addr,
     XP_ASSERT( !!name );
     XP_Bool canUse = addr_hasType( addr, COMMS_CONN_MQTT );
     if ( canUse ) {
-        KPState* state = loadState( dutil, xwe );
+        WITH_MUTEX( &dutil->kpMutex );
+        KPState* state = loadStateLocked( dutil, xwe );
         addPlayer( dutil, state, name, addr, modTime );
-        releaseState( dutil, xwe, state );
+        releaseStateLocked( dutil, xwe, state );
+        END_WITH_MUTEX();
     }
 
     XP_LOGFFV( "=>%s", boolToStr(canUse) );
@@ -261,9 +259,12 @@ kplr_addAddr( XW_DUtilCtxt* dutil, XWEnv xwe, const CommsAddrRec* addr,
 XP_Bool
 kplr_havePlayers( XW_DUtilCtxt* dutil, XWEnv xwe )
 {
-    KPState* state = loadState( dutil, xwe );
-    XP_Bool result = 0 < dll_length( &state->players->links );
-    releaseState( dutil, xwe, state );
+    XP_Bool result;
+    WITH_MUTEX( &dutil->kpMutex );
+    KPState* state = loadStateLocked( dutil, xwe );
+    result = 0 < dll_length( &state->players->links );
+    releaseStateLocked( dutil, xwe, state );
+    END_WITH_MUTEX();
     LOG_RETURNF( "%s", boolToStr(result) );
     return result;
 }
@@ -303,7 +304,8 @@ void
 kplr_getNames( XW_DUtilCtxt* dutil, XWEnv xwe, XP_Bool byDate,
                const XP_UCHAR** players, XP_U16* nFound )
 {
-    KPState* state = loadState( dutil, xwe );
+    WITH_MUTEX( &dutil->kpMutex );
+    KPState* state = loadStateLocked( dutil, xwe );
     if ( byDate ) {
         state->players = (KnownPlayer*)dll_sort( &state->players->links,
                                                  compByDate );
@@ -313,7 +315,8 @@ kplr_getNames( XW_DUtilCtxt* dutil, XWEnv xwe, XP_Bool byDate,
         state->players = (KnownPlayer*)dll_sort( &state->players->links,
                                                  compByName );
     }
-    releaseState( dutil, xwe, state );
+    releaseStateLocked( dutil, xwe, state );
+    END_WITH_MUTEX();
 }
 
 typedef struct _FindState {
@@ -350,8 +353,9 @@ XP_Bool
 kplr_getAddr( XW_DUtilCtxt* dutil, XWEnv xwe, const XP_UCHAR* name,
               CommsAddrRec* addr, XP_U32* lastMod )
 {
-    KPState* state = loadState( dutil, xwe );
     XP_Bool found = XP_FALSE;
+    WITH_MUTEX( &dutil->kpMutex );
+    KPState* state = loadStateLocked( dutil, xwe );
     KnownPlayer* kp = findByName( state, name );
     found = NULL != kp;
     if ( found ) {
@@ -360,7 +364,8 @@ kplr_getAddr( XW_DUtilCtxt* dutil, XWEnv xwe, const XP_UCHAR* name,
             *lastMod = kp->newestMod;
         }
     }
-    releaseState( dutil, xwe, state );
+    releaseStateLocked( dutil, xwe, state );
+    END_WITH_MUTEX();
     LOG_RETURNF( "%s", boolToStr(found) );
     return found;
 }
@@ -401,13 +406,15 @@ kplr_nameForAddress( XW_DUtilCtxt* dutil, XWEnv xwe,
                      const CommsAddrRec* addr )
 {
     MDevState ms = {.addr = addr};
-    KPState* state = loadState( dutil, xwe );
+    WITH_MUTEX( &dutil->kpMutex );
+    KPState* state = loadStateLocked( dutil, xwe );
 #ifdef DEBUG
     DLHead* head =
 #endif
         dll_map( &state->players->links, addrProc, NULL, &ms );
     XP_ASSERT( head == &state->players->links );
-    releaseState( dutil, xwe, state );
+    releaseStateLocked( dutil, xwe, state );
+    END_WITH_MUTEX();
 
     XP_LOGFF( "=> %s", ms.name );
     return ms.name;
@@ -425,7 +432,8 @@ kplr_renamePlayer( XW_DUtilCtxt* dutil, XWEnv xwe, const XP_UCHAR* oldName,
                    const XP_UCHAR* newName )
 {
     KP_Rslt result;
-    KPState* state = loadState( dutil, xwe );
+    WITH_MUTEX( &dutil->kpMutex );
+    KPState* state = loadStateLocked( dutil, xwe );
 
     KnownPlayer* kp = findByName( state, oldName );
     if ( !kp ) {
@@ -439,7 +447,8 @@ kplr_renamePlayer( XW_DUtilCtxt* dutil, XWEnv xwe, const XP_UCHAR* oldName,
         result = KP_OK;
     }
 
-    releaseState( dutil, xwe, state );
+    releaseStateLocked( dutil, xwe, state );
+    END_WITH_MUTEX();
     return result;
 }
 
@@ -474,12 +483,14 @@ KP_Rslt
 kplr_deletePlayer( XW_DUtilCtxt* dutil, XWEnv xwe, const XP_UCHAR* name )
 {
     KP_Rslt result = KP_OK;
-    KPState* state = loadState( dutil, xwe );
+    WITH_MUTEX( &dutil->kpMutex );
+    KPState* state = loadStateLocked( dutil, xwe );
 
     DelState ds = { .name = name, .state = state, .dutil = dutil,};
     state->players = (KnownPlayer*)
         dll_map( &state->players->links, delMapProc, delFreeProc, &ds );
-    releaseState( dutil, xwe, state );
+    releaseStateLocked( dutil, xwe, state );
+    END_WITH_MUTEX();
 
     return result;
 }
diff --git a/xwords4/common/smsproto.c b/xwords4/common/smsproto.c
index dcf18ae2b..3fc5350a5 100644
--- a/xwords4/common/smsproto.c
+++ b/xwords4/common/smsproto.c
@@ -24,6 +24,7 @@
 #include "smsproto.h"
 #include "comtypes.h"
 #include "strutils.h"
+#include "xwmutex.h"
 
 #define MAX_WAIT 3
 // # define MAX_MSG_LEN 50         /* for testing */
@@ -71,7 +72,7 @@ typedef struct _FromPhoneRec {
 struct SMSProto {
     XW_DUtilCtxt* dutil;
     pthread_t creator;
-    pthread_mutex_t mutex;
+    MutexState mutex;
     XP_U16 nNextID;
     int lastStoredSize;
     XP_U16 nToPhones;
@@ -120,7 +121,7 @@ SMSProto*
 smsproto_init( MPFORMAL XWEnv xwe, XW_DUtilCtxt* dutil )
 {
     SMSProto* state = (SMSProto*)XP_CALLOC( mpool, sizeof(*state) );
-    pthread_mutex_init( &state->mutex, NULL );
+    mtx_init( &state->mutex, XP_FALSE );
     state->dutil = dutil;
     MPASSIGN( state->mpool, mpool );
 
@@ -156,7 +157,7 @@ smsproto_free( SMSProto* state )
         }
         XP_ASSERT( !state->fromPhoneRecs ); /* above nulls this once empty */
 
-        pthread_mutex_destroy( &state->mutex );
+        mtx_destroy( &state->mutex );
 
         XP_FREEP( state->mpool, &state );
     }
@@ -220,7 +221,7 @@ smsproto_prepOutbound( SMSProto* state, XWEnv xwe, SMS_CMD cmd, XP_U32 gameID,
 {
     XP_USE( toPort );
     SMSMsgArray* result = NULL;
-    pthread_mutex_lock( &state->mutex );
+    WITH_MUTEX( &state->mutex );
 
 #if defined DEBUG
     Md5SumBuf sb;
@@ -260,7 +261,7 @@ smsproto_prepOutbound( SMSProto* state, XWEnv xwe, SMS_CMD cmd, XP_U32 gameID,
     XP_LOGF( "%s() => %p (count=%d, *waitSecs=%d)", __func__, result,
              !!result ? result->nMsgs : 0, *waitSecsP );
 
-    pthread_mutex_unlock( &state->mutex );
+    END_WITH_MUTEX();
     logResult( state, xwe, result, __func__ );
     return result;
 } /* smsproto_prepOutbound */
@@ -310,7 +311,7 @@ smsproto_prepInbound( SMSProto* state, XWEnv xwe, const XP_UCHAR* fromPhone,
 #endif
 
     SMSMsgArray* result = NULL;
-    pthread_mutex_lock( &state->mutex );
+    WITH_MUTEX( &state->mutex );
 
     XWStreamCtxt* stream = mkStream( state );
     stream_putBytes( stream, data, len );
@@ -380,14 +381,14 @@ smsproto_prepInbound( SMSProto* state, XWEnv xwe, const XP_UCHAR* fromPhone,
     XP_LOGFF( "=> %p (len=%d)", result, (!!result) ? result->nMsgs : 0 );
     logResult( state, xwe, result, __func__ );
 
-    pthread_mutex_unlock( &state->mutex );
+    END_WITH_MUTEX();
     return result;
 }
 
 void
 smsproto_freeMsgArray( SMSProto* state, SMSMsgArray* arr )
 {
-    pthread_mutex_lock( &state->mutex );
+    WITH_MUTEX( &state->mutex );
 
     for ( int ii = 0; ii < arr->nMsgs; ++ii ) {
         XP_U8** ptr = arr->format == FORMAT_LOC
@@ -409,7 +410,7 @@ smsproto_freeMsgArray( SMSProto* state, SMSMsgArray* arr )
     }
     XP_FREEP( state->mpool, ptr );
     XP_FREEP( state->mpool, &arr );
-    pthread_mutex_unlock( &state->mutex );
+    END_WITH_MUTEX();
 }
 
 #if defined DEBUG
diff --git a/xwords4/linux/scripts/netGamesTest.py b/xwords4/linux/scripts/netGamesTest.py
index c087319e1..0b3b08710 100755
--- a/xwords4/linux/scripts/netGamesTest.py
+++ b/xwords4/linux/scripts/netGamesTest.py
@@ -615,6 +615,7 @@ class Device():
         self._stats = stats
 
     def _checkScript(self):
+        assert os.path.exists(self.args.APP_NEW)
         if not os.path.exists(self.script):
             scriptArgs = ['exec']     # without exec means terminate() won't work
             if self.args.VALGRIND:
@@ -915,7 +916,7 @@ def mkParser():
 
     parser.add_argument('--timer-seconds', dest='TIMER_SECS', default=10, type=int,
                         help='Enable game timer with game this many seconds long')
-    parser.add_argument('--min-app-life', dest='MIN_APP_LIFE', default=5, type=int,
+    parser.add_argument('--min-app-life', dest='MIN_APP_LIFE', default=15, type=int,
                         help='Minimum number of seconds app will run after each launch')
 
     parser.add_argument('--with-sms', dest = 'WITH_SMS', action = 'store_true')