diff --git a/C/c_interface.c b/C/c_interface.c
index 8d6ff97df..99a17f769 100755
--- a/C/c_interface.c
+++ b/C/c_interface.c
@@ -2641,6 +2641,7 @@ YAP_InitConsult(int mode, const char *filename)
     return -1;
   sno = Yap_OpenStream(f, NULL, TermNil, Input_Stream_f );
   RECOVER_MACHINE_REGS();
+    UNLOCK(GLOBAL_Stream[sno].streamlock);
   return sno;
 }
 
@@ -2964,7 +2965,7 @@ YAP_Init(YAP_init_args *yap_init)
       */
       setBooleanGlobalPrologFlag(HALT_AFTER_CONSULT_FLAG, yap_init->HaltAfterConsult );
     }
-    /* tell the system who should cope with interruptions */
+    /* tell the system who should cope with interrupts */
     Yap_ExecutionMode = yap_init->ExecutionMode;
     if (do_bootstrap) {
       restore_result = YAP_BOOT_FROM_PROLOG;
diff --git a/C/qlyr.c b/C/qlyr.c
index cefbd535b..29aa9e0d9 100755
--- a/C/qlyr.c
+++ b/C/qlyr.c
@@ -741,6 +741,7 @@ p_get_header( USES_REGS1 )
   FILE *stream;
   Term t1 = Deref(ARG1);
   Atom at;
+    Int rc;
 
   if (IsVarTerm(t1)) {
     Yap_Error(INSTANTIATION_ERROR,t1,"read_program/3");
@@ -750,8 +751,9 @@ p_get_header( USES_REGS1 )
     return FALSE;
   }
   if ((at = get_header( stream )) == NIL)
-    return FALSE;
-  return Yap_unify( ARG2, MkAtomTerm( at ) );
+    rc = FALSE;
+  else rc = Yap_unify( ARG2, MkAtomTerm( at ) );
+    return rc;
 }
 
 static void
diff --git a/C/threads.c b/C/threads.c
index 3082a0002..b7fcc7892 100644
--- a/C/threads.c
+++ b/C/threads.c
@@ -52,7 +52,7 @@ blob_type_t PL_Message_Queue = {
 #if DEBUG_LOCKS||DEBUG_PE_LOCKS
 
 int debug_locks = FALSE, debug_pe_locks = FALSE;
-static Int p_debug_locks( USES_REGS1 ) { debugf=stdout; debug_pe_locks = 1; return TRUE; }
+static Int p_debug_locks( USES_REGS1 ) { debug_pe_locks = 1; return TRUE; }
 
 static Int p_nodebug_locks( USES_REGS1 ) { debug_locks = 0; debug_pe_locks = 0; return TRUE; }
 
@@ -1590,8 +1590,6 @@ Yap_InitFirstWorkerThreadHandle(void)
   LOCAL_ThreadHandle.ref_count = 1;
 }
 
-FILE *debugf;
-
 void Yap_InitThreadPreds(void)
 {
 
diff --git a/C/tracer.c b/C/tracer.c
index 19c240c37..72ed092d9 100644
--- a/C/tracer.c
+++ b/C/tracer.c
@@ -97,10 +97,19 @@ check_trail_consistency(void) {
 
 CELL old_value = 0L, old_value2 = 0L;
 
-void jmp_deb(int);
+void jmp_deb(int), jmp_deb2(void);
 
 void
-jmp_deb(int i) {if (i) printf("Here we go\n"); else jmp_deb(0);}
+jmp_deb2( void )
+{
+    fprintf(stderr,"Here\n");
+}
+
+void
+jmp_deb(int i) {
+    if (i) printf("Here we go %ld\n", old_value++);
+    if (old_value == 716) jmp_deb2();
+    }
 
 struct various_codes *sc;
 
diff --git a/OPTYap/locks_pthread.h b/OPTYap/locks_pthread.h
index 2414dd069..9229c0ab0 100755
--- a/OPTYap/locks_pthread.h
+++ b/OPTYap/locks_pthread.h
@@ -22,13 +22,13 @@
 #include <pthread.h>
 
 //#define DEBUG_PE_LOCKS 1
-#define DEBUG_LOCKS 1
+//#define DEBUG_LOCKS 1
 #include <stdio.h>
 
 int Yap_ThreadID( void );
-#define debugf stdout
+#define debugf ( stderr ? stderr : stdout )
 
-#define INIT_LOCK(LOCK_VAR)    (void)(fprintf(debugf, "[%d] %s:%d: LOCK(%p)\n",  Yap_ThreadID(),__BASE_FILE__, __LINE__,&(LOCK_VAR))  && pthread_mutex_init(&(LOCK_VAR), NULL) )
+#define INIT_LOCK(LOCK_VAR)    pthread_mutex_init(&(LOCK_VAR), NULL)
 #define DESTROY_LOCK(LOCK_VAR) pthread_mutex_destroy(&(LOCK_VAR))
 #define TRY_LOCK(LOCK_VAR)     pthread_mutex_trylock(&(LOCK_VAR))
 #if DEBUG_LOCKS
diff --git a/os/charsio.c b/os/charsio.c
index b5bae2466..ce095b1c6 100644
--- a/os/charsio.c
+++ b/os/charsio.c
@@ -808,11 +808,12 @@ peek_code ( USES_REGS1 )
     return FALSE;
   if (GLOBAL_Stream[sno].status & Binary_Stream_f) {
     UNLOCK(GLOBAL_Stream[sno].streamlock);
-    Yap_Error(PERMISSION_ERROR_INPUT_BINARY_STREAM, ARG1, "peek_code/2");
+    PlIOError(PERMISSION_ERROR_INPUT_BINARY_STREAM, ARG1, "peek_code/2");
     return FALSE;
   }
   if ((ch =  dopeek( sno )) < 0)
     return false;
+    UNLOCK(GLOBAL_Stream[sno].streamlock);
   return(Yap_unify_constant(ARG2,MkIntTerm(ch)));
 }
 
@@ -841,6 +842,7 @@ peek_code_1 ( USES_REGS1 )
   }
   if ((ch =  dopeek( sno )) < 0)
     return false;
+    UNLOCK(GLOBAL_Stream[sno].streamlock);
   return(Yap_unify_constant(ARG2,MkIntTerm(ch)));
 }
 
@@ -857,7 +859,7 @@ peek_byte ( USES_REGS1 )
 {				/* at_end_of_stream */
   /* the next character is a EOF */ 
   int sno = Yap_CheckStream (ARG1, Input_Stream_f, "peek/2");
-  Int ch;
+    Int ch;
 
   if (sno < 0)
     return(FALSE);
@@ -868,6 +870,7 @@ peek_byte ( USES_REGS1 )
   }
   if ((ch =  dopeek( sno )) < 0)
     return false;
+    UNLOCK(GLOBAL_Stream[sno].streamlock);
   return(Yap_unify_constant(ARG2,MkIntTerm(ch)));
 }
 
diff --git a/os/files.c b/os/files.c
index 893e3806b..e86529109 100644
--- a/os/files.c
+++ b/os/files.c
@@ -347,13 +347,15 @@ file_size(USES_REGS1)
 	// there
 	struct stat file_stat;
 	if (fstat(fileno(GLOBAL_Stream[sno].file), &file_stat) < 0) {
+        UNLOCK(GLOBAL_Stream[sno].streamlock);
 	  PlIOError( PERMISSION_ERROR_INPUT_STREAM, ARG1, "%s in file_size/2", strerror(errno));
 	  return false;
 	}
 	// and back again
-
+      UNLOCK(GLOBAL_Stream[sno].streamlock);
 	return Yap_unify_constant( ARG2, MkIntegerTerm( file_stat.st_size) );
   }
+    UNLOCK(GLOBAL_Stream[sno].streamlock);
   return false;
 }
 
diff --git a/os/iopreds.c b/os/iopreds.c
index b62a144cf..a463cebe8 100644
--- a/os/iopreds.c
+++ b/os/iopreds.c
@@ -1650,7 +1650,7 @@ Yap_OpenStream(FILE *fd, char *name, Term file_name, int flags)
       if (sname == AtomUser) {
 	if (kind & Input_Stream_f) {
 	  if (kind & (Output_Stream_f|Append_Stream_f)) {
-	    Yap_Error(PERMISSION_ERROR_INPUT_STREAM, arg,
+	    PlIOError(PERMISSION_ERROR_INPUT_STREAM, arg,
 		      "ambiguous use of 'user' as a stream");
 	    return (-1);	    
 	  }
@@ -1690,6 +1690,7 @@ Yap_OpenStream(FILE *fd, char *name, Term file_name, int flags)
 	  Yap_Error(PERMISSION_ERROR_OUTPUT_STREAM, arg, msg);
 	return (-1);
       }
+      jmp_deb(1);
     return (sno);
   }
 
diff --git a/os/readterm.c b/os/readterm.c
index 1bc188dd6..426443ef7 100644
--- a/os/readterm.c
+++ b/os/readterm.c
@@ -824,8 +824,8 @@ read2 ( USES_REGS1 )
   if (inp_stream == -1) {
     return(FALSE);
   }
-  UNLOCK(GLOBAL_Stream[inp_stream].streamlock);
   out = Yap_read_term(inp_stream, TermNil, 1);
+    UNLOCK(GLOBAL_Stream[inp_stream].streamlock);
   return out && Yap_unify(ARG2, out);
 }
     
@@ -938,7 +938,8 @@ Yap_StringToTerm(const char *s, size_t len, encoding_t enc, int prio, Term *bind
         
   rval = Yap_read_term(stream, ctl, 3);
   Yap_CloseStream(stream);
-  if (bindings) {
+    UNLOCK(GLOBAL_Stream[stream].streamlock);
+  if (rval && bindings) {
     *bindings = Yap_GetFromSlot( sl );
     Yap_RecoverSlots( sl, 1 PASS_REGS);
   }
diff --git a/os/streams.c b/os/streams.c
index 98a21819b..cc7ce2966 100644
--- a/os/streams.c
+++ b/os/streams.c
@@ -102,29 +102,35 @@ static void CloseStream(int sno);
 FILE  *Yap_GetInputStream(Term t, const char *msg)
 { 
   int sno = Yap_CheckStream (t, Input_Stream_f, msg);
+    FILE *rc;
 
   if(!(GLOBAL_Stream[sno].status & (Tty_Stream_f|Socket_Stream_f|Pipe_Stream_f)))
-    return GLOBAL_Stream[sno].file;
-  return NULL;
+    rc = GLOBAL_Stream[sno].file;
+    else
+      rc = NULL;
+    UNLOCK(GLOBAL_Stream[sno].streamlock);
+    return rc;
 }
 
 FILE  *Yap_GetOutputStream(Term t, const char *msg)
 { 
    int sno = Yap_CheckStream (t, Output_Stream_f, msg);
+    FILE *rc;
 
    if(!(GLOBAL_Stream[sno].status  & (Tty_Stream_f|Socket_Stream_f)))
-      return GLOBAL_Stream[sno].file;
-
-   return NULL;
+       rc = GLOBAL_Stream[sno].file;
+   else
+       rc = NULL;
+    UNLOCK(GLOBAL_Stream[sno].streamlock);
+    return rc;
 }
 
 int
 GetFreeStreamD(void)
 {
     CACHE_REGS
-  int sno;
-
-  for (sno = 0; sno < MaxStreams; ++sno) {
+    int sno;
+    for (sno = 0; sno < MaxStreams; ++sno) {
     LOCK(GLOBAL_Stream[sno].streamlock);
     if (GLOBAL_Stream[sno].status & Free_Stream_f) {
       break;
@@ -208,7 +214,6 @@ static Int
 is_input ( int sno USES_REGS )
 {				/* '$set_output'(+Stream,-ErrorMessage)  */
   bool rc = GLOBAL_Stream[sno].status & Input_Stream_f;
-  UNLOCK(GLOBAL_Stream[sno].streamlock);
   return rc;
 }
 
@@ -216,14 +221,12 @@ static Int
 is_output ( int sno USES_REGS )
 {				/* '$set_output'(+Stream,-ErrorMessage)  */
   bool rc = GLOBAL_Stream[sno].status & (Output_Stream_f|Append_Stream_f);
-  UNLOCK(GLOBAL_Stream[sno].streamlock);
   return rc;
 }
 
 static Int
 has_bom ( int sno, Term t2 USES_REGS )
 {				/* '$set_output'(+Stream,-ErrorMessage)  */
-  UNLOCK(GLOBAL_Stream[sno].streamlock);
   bool rc = GLOBAL_Stream[sno].status & Seekable_Stream_f;
   if (!IsVarTerm(t2) && !boolean(t2)) {
     return FALSE;
@@ -234,11 +237,11 @@ has_bom ( int sno, Term t2 USES_REGS )
     return Yap_unify_constant(t2, TermFalse);
   }
 }
+
 static Int
 has_reposition ( int sno, Term t2 USES_REGS )
 {				/* '$set_output'(+Stream,-ErrorMessage)  */
   bool rc = GLOBAL_Stream[sno].status & Seekable_Stream_f;
-  UNLOCK(GLOBAL_Stream[sno].streamlock);
   if (!IsVarTerm(t2) && !boolean(t2)) {
     return FALSE;
   }
@@ -284,7 +287,6 @@ representation_error ( int sno, Term t2 USES_REGS )
 {
   stream_flags_t flags = GLOBAL_Stream[sno].status & (RepError_Xml_f|RepError_Prolog_f);
   /* '$representation_error'(+Stream,-ErrorMessage)  */
-  UNLOCK(GLOBAL_Stream[sno].streamlock);
   if (!IsVarTerm(t2) && isatom(t2)) {
     return false;    
   }
@@ -308,7 +310,6 @@ file_name ( int sno, Term t2 USES_REGS )
     rc = MkAtomTerm(Yap_LookupAtom(name));
   else
     return false;
-  UNLOCK(GLOBAL_Stream[sno].streamlock);
   if (!IsVarTerm(t2) && !isatom(t2)) {
     return FALSE;
   }
@@ -320,7 +321,6 @@ file_no ( int sno, Term t2 USES_REGS )
 {
   int f = Yap_GetStreamFd(sno);
   Term rc = MkIntTerm(f) ;
-  UNLOCK(GLOBAL_Stream[sno].streamlock);
   if (!IsVarTerm(t2) && !IsIntTerm(t2)) {
     return false;
   }
@@ -355,7 +355,6 @@ has_close_on_abort ( int sno, Term t2 USES_REGS )
 static bool
 has_encoding ( int sno, Term t2 USES_REGS )
 {				/* '$set_output'(+Stream,-ErrorMessage)  */
-  UNLOCK(GLOBAL_Stream[sno].streamlock);
   if (!IsVarTerm(t2) && !(isatom(t2))) {
     return FALSE;
   }
@@ -375,7 +374,6 @@ static bool
 found_eof ( int sno, Term t2 USES_REGS )
 {				/* '$set_output'(+Stream,-ErrorMessage)  */
   stream_flags_t flags = GLOBAL_Stream[sno].status & (Past_Eof_Stream_f|Eof_Stream_f);
-  UNLOCK(GLOBAL_Stream[sno].streamlock);
   if (!IsVarTerm(t2) && !(isatom(t2))) {
     return FALSE;
   }
@@ -391,7 +389,6 @@ static bool
 stream_mode ( int sno, Term t2 USES_REGS )
 {				/* '$set_output'(+Stream,-ErrorMessage)  */
   stream_flags_t flags = GLOBAL_Stream[sno].status & (Input_Stream_f|Output_Stream_f|Append_Stream_f);
-  UNLOCK(GLOBAL_Stream[sno].streamlock);
   if (!IsVarTerm(t2) && !(isatom(t2))) {
     return FALSE;
   }
@@ -408,7 +405,6 @@ static bool
 stream_tty ( int sno, Term t2 USES_REGS )
 {				/* '$set_output'(+Stream,-ErrorMessage)  */
   stream_flags_t flags = GLOBAL_Stream[sno].status & (Tty_Stream_f);
-  UNLOCK(GLOBAL_Stream[sno].streamlock);
   if (!IsVarTerm(t2) && !(isatom(t2))) {
     return FALSE;
   }
@@ -421,7 +417,6 @@ static bool
 stream_type ( int sno, Term t2 USES_REGS )
 {				/* '$set_output'(+Stream,-ErrorMessage)  */
   stream_flags_t flags = GLOBAL_Stream[sno].status & (Binary_Stream_f);
-  UNLOCK(GLOBAL_Stream[sno].streamlock);
   if (!IsVarTerm(t2) && !(isatom(t2))) {
     return FALSE;
   }
@@ -434,7 +429,6 @@ static bool
 stream_position ( int sno, Term t2 USES_REGS )
 {				/* '$set_output'(+Stream,-ErrorMessage)  */
   Term tout = StreamPosition(sno);
-  UNLOCK(GLOBAL_Stream[sno].streamlock);
   return Yap_unify (t2, tout);
 }
 
@@ -474,7 +468,6 @@ static bool
 eof_action ( int sno, Term t2 USES_REGS )
 {				/* '$set_output'(+Stream,-ErrorMessage)  */
   stream_flags_t flags = GLOBAL_Stream[sno].status & (Eof_Error_Stream_f|Reset_Eof_Stream_f|Push_Eof_Stream_f);
-  UNLOCK(GLOBAL_Stream[sno].streamlock);
   if (!IsVarTerm(t2) && !(isatom(t2))) {
     return FALSE;
   }
@@ -706,6 +699,7 @@ do_set_stream (int sno, Term opts USES_REGS)
 
   args = Yap_ArgListToVector ( opts, set_stream_defs, SET_STREAM_END  );
   if (args == NULL) {
+      UNLOCK(GLOBAL_Stream[sno].streamlock);
     return false;
   }
   for (i=0; i < SET_STREAM_END; i ++) {
@@ -747,7 +741,7 @@ do_set_stream (int sno, Term opts USES_REGS)
 	 } else {
 	   LOCAL_Error_TYPE = DOMAIN_ERROR_OUT_OF_RANGE;
 	   LOCAL_ErrorMessage = "in set_stream/2:eof_action";
-	   return false;
+	   rc = false;
 	 }
 	 break;
       case SET_STREAM_FILE_NAME:
@@ -780,7 +774,7 @@ do_set_stream (int sno, Term opts USES_REGS)
 	 } else {
 	   LOCAL_Error_TYPE = DOMAIN_ERROR_OUT_OF_RANGE;
 	   LOCAL_ErrorMessage = "in set_stream/2:eof_action";
-	   return false;
+	   rc = false;
 	 }
        }
        break;
@@ -1265,13 +1259,13 @@ set_stream_position ( USES_REGS1 )
     }
     if (!(GLOBAL_Stream[sno].status & Seekable_Stream_f) ) {
       UNLOCK(GLOBAL_Stream[sno].streamlock);
-      Yap_Error(PERMISSION_ERROR_REPOSITION_STREAM, ARG1,"set_stream_position/2");
+      PlIOError(PERMISSION_ERROR_REPOSITION_STREAM, ARG1,"set_stream_position/2");
       return(FALSE);
     }
     if (fseek (GLOBAL_Stream[sno].file, 0L, SEEK_END) == -1) {
-      UNLOCK(GLOBAL_Stream[sno].streamlock);
-      Yap_Error(SYSTEM_ERROR, tp, 
-	    "fseek failed for set_stream_position/2");
+        UNLOCK(GLOBAL_Stream[sno].streamlock);
+      PlIOError(SYSTEM_ERROR, tp,
+	    "fseek failed for set_stream_position/2: %s", strerror(errno));
       return(FALSE);
     }
     GLOBAL_Stream[sno].stream_getc = PlGetc;
@@ -1431,7 +1425,7 @@ Yap_StreamToFileNo(Term t)
     UNLOCK(GLOBAL_Stream[sno].streamlock);
     return(GLOBAL_Stream[sno].u.socket.fd);
 #endif
-  } else if (GLOBAL_Stream[sno].status & (Null_Stream_f|InMemory_Stream_f)) {
+  } else if (GLOBAL_Stream[sno].status & (Null_Stream_f)) {
     UNLOCK(GLOBAL_Stream[sno].streamlock);
     return(-1);
   } else {
@@ -1458,15 +1452,17 @@ FILE *
 Yap_FileDescriptorFromStream(Term t)
 {
   int sno = Yap_CheckStream (t, Input_Stream_f|Output_Stream_f, "FileDescriptorFromStream");
+    FILE *rc;
   if (sno < 0)
     return NULL;
   if (GLOBAL_Stream[sno].status & (Null_Stream_f|
-		InMemory_Stream_f|
 		Socket_Stream_f|
 		Pipe_Stream_f|
 		Free_Stream_f))
-    return NULL;
-  return GLOBAL_Stream[sno].file;
+    rc = NULL;
+  else rc = GLOBAL_Stream[sno].file;
+    UNLOCK(GLOBAL_Stream[sno].streamlock);
+    return rc;
 }
 
 void