make sure we separate betwen async exceptions and synchroneous.

C/absmi.c

@@ -1861,7 +1861,6 @@ Yap_absmi(int inp)
 #else
       B = B->cp_b;
 #endif	/* YAPOR */
-      goto fail;
       ENDBOp();
 
 #ifdef YAPOR

C/c_interface.c

@@ -480,6 +480,7 @@ X_API int     STD_PROTO(YAP_RecoverSlots,(int));
 X_API Int     STD_PROTO(YAP_ArgsToSlots,(int));
 X_API void    STD_PROTO(YAP_SlotsToArgs,(int, Int));
 X_API void    STD_PROTO(YAP_Throw,(Term));
+X_API void    STD_PROTO(YAP_AsyncThrow,(Term));
 X_API void    STD_PROTO(YAP_Halt,(int));
 X_API Term   *STD_PROTO(YAP_TopOfLocalStack,(void));
 X_API void   *STD_PROTO(YAP_Predicate,(Atom,UInt,Term));
@@ -2833,6 +2834,16 @@ YAP_Throw(Term t)
   RECOVER_MACHINE_REGS();
 }
 
+X_API void
+YAP_AsyncThrow(Term t)
+{
+  BACKUP_MACHINE_REGS();
+  Yap_PrologMode |= AsyncIntMode;
+  Yap_JumpToEnv(t);
+  Yap_PrologMode &= ~AsyncIntMode;
+  RECOVER_MACHINE_REGS();
+}
+
 X_API void
 YAP_Halt(int i)
 {

C/errors.c

@@ -455,7 +455,9 @@ Yap_Error(yap_error_number type, Term where, char *format,...)
     where = TermNil;
     Yap_PrologMode &= ~AbortMode;
     Yap_PrologMode |= InErrorMode;
-    Yap_signal(YAP_FAIL_SIGNAL);
+    /* make sure failure will be seen at next port */
+    if (Yap_PrologMode & AsyncIntMode)
+      Yap_signal(YAP_FAIL_SIGNAL);
     P = FAILCODE;
   } else {
     if (IsVarTerm(where)) {

C/exec.c

@@ -1511,7 +1511,10 @@ JumpToEnv(Term t) {
 	EX = BallTerm;
 	BallTerm = NULL;
 	P = (yamop *)FAILCODE;
-	Yap_signal(YAP_FAIL_SIGNAL);
+	/* make sure failure will be seen at next port */
+	if (Yap_PrologMode & AsyncIntMode) {
+	  Yap_signal(YAP_FAIL_SIGNAL);
+	}
 	HB = B->cp_h;
 	return TRUE;
       }
@@ -1553,7 +1556,9 @@ JumpToEnv(Term t) {
   /* B->cp_h = H; */
   /* I could backtrack here, but it is easier to leave the unwinding
      to the emulator */
-  Yap_signal(YAP_FAIL_SIGNAL);
+  if (Yap_PrologMode & AsyncIntMode) {
+    Yap_signal(YAP_FAIL_SIGNAL);
+  }
   P = (yamop *)FAILCODE;
   HB = B->cp_h;
   /* try to recover space */

C/sysbits.c

@@ -1545,6 +1545,7 @@ void (*handler)(int);
 
 static int
 InteractSIGINT(int ch) {
+  Yap_PrologMode |= AsyncIntMode;
   switch (ch) {
   case 'a':
     /* abort computation */
@@ -1554,40 +1555,49 @@ InteractSIGINT(int ch) {
       Yap_Error(PURE_ABORT, TermNil, "abort from console");
       /* in case someone mangles the P register */
     }
+    Yap_PrologMode &= ~AsyncIntMode;
     return -1;
   case 'b':
     /* continue */
     Yap_signal (YAP_BREAK_SIGNAL);
+    Yap_PrologMode &= ~AsyncIntMode;
     return 1;
   case 'c':
     /* continue */
     return 1;
   case 'd':
     Yap_signal (YAP_DEBUG_SIGNAL);
+    Yap_PrologMode &= ~AsyncIntMode;
     /* enter debug mode */
     return 1;
   case 'e':
     /* exit */
+    Yap_PrologMode &= ~AsyncIntMode;
     Yap_exit(0);
     return -1;
   case 'g':
     /* exit */
     Yap_signal (YAP_STACK_DUMP_SIGNAL);
+    Yap_PrologMode &= ~AsyncIntMode;
     return -1;
   case 't':
     /* start tracing */
     Yap_signal (YAP_TRACE_SIGNAL);
+    Yap_PrologMode &= ~AsyncIntMode;
     return 1;
 #ifdef LOW_LEVEL_TRACER
   case 'T':
     toggle_low_level_trace();
+    Yap_PrologMode &= ~AsyncIntMode;
     return 1;
 #endif
   case 's':
     /* show some statistics */
     Yap_signal (YAP_STATISTICS_SIGNAL);
+    Yap_PrologMode &= ~AsyncIntMode;
     return 1;
   case EOF:
+    Yap_PrologMode &= ~AsyncIntMode;
     return(0);
     break;
   case 'h':
@@ -1598,6 +1608,7 @@ InteractSIGINT(int ch) {
     fprintf(Yap_stderr, "  a for abort\n  c for continue\n  d for debug\n");
     fprintf(Yap_stderr, "  e for exit\n  g for stack dump\n  s for statistics\n  t for trace\n");
     fprintf(Yap_stderr, "  b for break\n");
+    Yap_PrologMode &= ~AsyncIntMode;
     return(0);
   }
 }

H/Yap.h

@@ -1187,6 +1187,7 @@ typedef enum
   UserCCallMode = 0x4000,	/* In User C-call Code */
   MallocMode = 0x8000,		/* Doing malloc, realloc, free */
   SystemMode = 0x10000,		/* in system mode */
+  AsyncIntMode = 0x20000	/* YAP has just been interrupted from the outside */
 } prolog_exec_mode;
 
 extern Int Yap_PrologMode;

include/YapInterface.h

@@ -435,6 +435,9 @@ extern X_API void PROTO(YAP_SlotsToArgs,(int, YAP_Int));
 /*  void  YAP_Throw()  */
 extern X_API void PROTO(YAP_Throw,(YAP_Term));
 
+/*  void  YAP_AsyncThrow()  */
+extern X_API void PROTO(YAP_AsyncThrow,(YAP_Term));
+
 /*  int  YAP_LookupModule()  */
 #define YAP_LookupModule(T)  (T)