Enhance enif_has_pending_exception

Sverker Eriksson came up with the following idea: to handle a future
ability for NIFs to raise more than just badarg exceptions, modify the
recently-added enif_has_pending_exception function to take a second
argument: a pointer to ERL_NIF_TERM. If this argument is a null
pointer, ignore it. Otherwise, if the first argument, an ErlNifEnv*,
has an associated exception, set the pointed-to ERL_NIF_TERM of the
second argument to the value of the exception term. Add new tests and
documentation for this modification.

5 files changed, 41 insertions, 21 deletions

diff --git a/erts/doc/src/erl_nif.xml b/erts/doc/src/erl_nif.xml
index 4bad8b253c..155aee2f42 100644
--- a/erts/doc/src/erl_nif.xml
+++ b/erts/doc/src/erl_nif.xml
@@ -778,11 +778,17 @@ typedef enum {
       and return true, or return false if <c>term</c> is not an unsigned integer or is
       outside the bounds of type <c>unsigned long</c>.</p></desc>
     </func>
-    <func><name><ret>int</ret><nametext>enif_has_pending_exception(ErlNifEnv* env)</nametext></name>
+    <func><name><ret>int</ret><nametext>enif_has_pending_exception(ErlNifEnv* env, ERL_NIF_TERM* reason)</nametext></name>
       <fsummary>Check if an exception has been raised.</fsummary>
       <desc><p>Return true if a pending exception is associated
-      with the environment <c>env</c>. The only possible exception is currently
-      <c>badarg</c> (see <seealso marker="#enif_make_badarg">enif_make_badarg</seealso>).</p></desc>
+      with the environment <c>env</c>. If <c>reason</c> is a null pointer, ignore it.
+      Otherwise, if there's a pending exception associated with <c>env</c>, set the ERL_NIF_TERM
+      to which <c>reason</c> points to the value of the exception's term. For example, if
+      <seealso marker="#enif_make_badarg">enif_make_badarg</seealso> is called to set a
+      pending <c>badarg</c> exception, a subsequent call to <c>enif_has_pending_exception(env, &amp;reason)</c>
+      will set <c>reason</c> to the atom <c>badarg</c>, then return true.</p>
+      <p>See also: <seealso marker="#enif_make_badarg">enif_make_badarg</seealso>.</p>
+      </desc>
     </func>
     <func><name><ret>int</ret><nametext>enif_inspect_binary(ErlNifEnv* env, ERL_NIF_TERM bin_term, ErlNifBinary* bin)</nametext></name>
       <fsummary>Inspect the content of a binary</fsummary>
diff --git a/erts/emulator/beam/erl_nif.c b/erts/emulator/beam/erl_nif.c
index 7876785a76..36da6519f7 100644
--- a/erts/emulator/beam/erl_nif.c
+++ b/erts/emulator/beam/erl_nif.c
@@ -741,8 +741,11 @@ Eterm enif_make_badarg(ErlNifEnv* env)
     BIF_ERROR(env->proc, BADARG);
 }
 
-int enif_has_pending_exception(ErlNifEnv* env)
+int enif_has_pending_exception(ErlNifEnv* env, ERL_NIF_TERM* reason)
 {
+    if (env->exception_thrown && reason != NULL) {
+	*reason = am_badarg;
+    }
     return env->exception_thrown;
 }
 
diff --git a/erts/emulator/beam/erl_nif_api_funcs.h b/erts/emulator/beam/erl_nif_api_funcs.h
index bdcbb32c46..fe25c803ec 100644
--- a/erts/emulator/beam/erl_nif_api_funcs.h
+++ b/erts/emulator/beam/erl_nif_api_funcs.h
@@ -156,7 +156,7 @@ ERL_NIF_API_FUNC_DECL(int, enif_map_iterator_next, (ErlNifEnv *env, ErlNifMapIte
 ERL_NIF_API_FUNC_DECL(int, enif_map_iterator_prev, (ErlNifEnv *env, ErlNifMapIterator *iter));
 ERL_NIF_API_FUNC_DECL(int, enif_map_iterator_get_pair, (ErlNifEnv *env, ErlNifMapIterator *iter, ERL_NIF_TERM *key, ERL_NIF_TERM *value));
 ERL_NIF_API_FUNC_DECL(ERL_NIF_TERM,enif_schedule_nif,(ErlNifEnv*,const char*,int,ERL_NIF_TERM (*)(ErlNifEnv*,int,const ERL_NIF_TERM[]),int,const ERL_NIF_TERM[]));
-ERL_NIF_API_FUNC_DECL(int, enif_has_pending_exception, (ErlNifEnv *env));
+ERL_NIF_API_FUNC_DECL(int, enif_has_pending_exception, (ErlNifEnv *env, ERL_NIF_TERM* reason));
 
 /*
 ** ADD NEW ENTRIES HERE (before this comment) !!!
diff --git a/erts/emulator/test/nif_SUITE.erl b/erts/emulator/test/nif_SUITE.erl
index c35c71dd5b..434d1c38d0 100644
--- a/erts/emulator/test/nif_SUITE.erl
+++ b/erts/emulator/test/nif_SUITE.erl
@@ -1387,7 +1387,7 @@ is_checks(Config) when is_list(Config) ->
 			self(), hd(erlang:ports()), [], [1,9,9,8],
 			{hejsan, "hejsan", [$h,"ejs",<<"an">>]}, -18446744073709551616.2e2),
     try
-        ?line error = check_is_exception(),
+        ?line check_is_exception(),
         ?line throw(expected_badarg)
     catch
         error:badarg ->
@@ -1599,9 +1599,9 @@ dirty_nif_exception(Config) when is_list(Config) ->
 	N when is_integer(N) ->
 	    ensure_lib_loaded(Config),
 	    try
-		%% this checks that the expected exception
-		%% occurs when the NIF returns the result
-		%% of enif_make_badarg directly
+		%% this checks that the expected exception occurs when the
+		%% dirty NIF returns the result of enif_make_badarg
+		%% directly
 	        call_dirty_nif_exception(1),
 	        ?t:fail(expected_badarg)
 	    catch
@@ -1611,10 +1611,9 @@ dirty_nif_exception(Config) when is_list(Config) ->
 		    ok
 	    end,
 	    try
-		%% this checks that the expected exception
-		%% occurs when the NIF calls enif_make_badarg
-		%% at some point but then returns a value that
-		%% isn't an exception
+		%% this checks that the expected exception occurs when the
+		%% dirty NIF calls enif_make_badarg at some point but then
+		%% returns a value that isn't an exception
 	        call_dirty_nif_exception(0),
 	        ?t:fail(expected_badarg)
 	    catch
@@ -1631,6 +1630,9 @@ dirty_nif_exception(Config) when is_list(Config) ->
 nif_exception(Config) when is_list(Config) ->
     ensure_lib_loaded(Config),
     try
+	%% this checks that the expected exception occurs when the NIF
+	%% calls enif_make_badarg at some point but then tries to return a
+	%% value that isn't an exception
 	call_nif_exception(),
 	?t:fail(expected_badarg)
     catch
diff --git a/erts/emulator/test/nif_SUITE_data/nif_SUITE.c b/erts/emulator/test/nif_SUITE_data/nif_SUITE.c
index 58d9a9a88c..95e361690f 100644
--- a/erts/emulator/test/nif_SUITE_data/nif_SUITE.c
+++ b/erts/emulator/test/nif_SUITE_data/nif_SUITE.c
@@ -883,16 +883,19 @@ static ERL_NIF_TERM check_is(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[]
  *
  * This function is separate from check_is because it calls enif_make_badarg
  * and so it must return the badarg exception as its return value. Thus, the
- * badarg exception indicates success. Failure is indicated by returning an
- * error atom.
+ * badarg exception indicates success.
  */
 static ERL_NIF_TERM check_is_exception(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[])
 {
+    ERL_NIF_TERM badarg, exc_term;
     ERL_NIF_TERM error_atom = enif_make_atom(env, "error");
-    ERL_NIF_TERM badarg = enif_make_badarg(env);
-    if (enif_is_exception(env, error_atom)) return error_atom;
-    if (!enif_is_exception(env, badarg)) return error_atom;
-    if (!enif_has_pending_exception(env)) return error_atom;
+    ERL_NIF_TERM badarg_atom = enif_make_atom(env, "badarg");
+    assert(!enif_is_exception(env, error_atom));
+    badarg = enif_make_badarg(env);
+    assert(enif_is_exception(env, badarg));
+    assert(enif_has_pending_exception(env, NULL));
+    assert(enif_has_pending_exception(env, &exc_term));
+    assert(enif_is_identical(exc_term, badarg_atom));
     return badarg;
 }
 
@@ -1621,7 +1624,7 @@ static ERL_NIF_TERM call_dirty_nif_exception(ErlNifEnv* env, int argc, const ERL
 	for (i = 1; i < 255; i++)
 	    args[i] = enif_make_int(env, i);
 	return enif_schedule_nif(env, "call_dirty_nif_exception", ERL_NIF_DIRTY_JOB_CPU_BOUND,
-				 call_dirty_nif_exception, 255, argv);
+				 call_dirty_nif_exception, 255, args);
     }
     case 2: {
         int return_badarg_directly;
@@ -1660,7 +1663,13 @@ static ERL_NIF_TERM call_dirty_nif_zero_args(ErlNifEnv* env, int argc, const ERL
  */
 static ERL_NIF_TERM call_nif_exception(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[])
 {
+    ERL_NIF_TERM exc_term;
+    ERL_NIF_TERM badarg_atom = enif_make_atom(env, "badarg");
+
     /* ignore return value */ enif_make_badarg(env);
+    assert(enif_has_pending_exception(env, NULL));
+    assert(enif_has_pending_exception(env, &exc_term));
+    assert(enif_is_identical(badarg_atom, exc_term));
     return enif_make_atom(env, "ok");
 }
 
@@ -1696,7 +1705,7 @@ static ERL_NIF_TERM call_nif_nan_or_inf(ErlNifEnv* env, int argc, const ERL_NIF_
     }
     res = enif_make_double(env, val);
     assert(enif_is_exception(env, res));
-    assert(enif_has_pending_exception(env));
+    assert(enif_has_pending_exception(env, NULL));
     if (strcmp(arg, "tuple") == 0) {
         return enif_make_tuple2(env, argv[0], res);
     } else {