Add enif_raise_exception

Add enif_raise_exception function to allow NIFs to raise error
exceptions holding any Erlang terms. This does not replace or
deprecate the enif_make_badarg function, though, because raising
badarg errors is so idiomatic in NIFs. Reimplement enif_make_badarg on
top of enif_raise_exception. Add new tests for enif_raise_exception
for both normal and dirty NIFs. Add documentation for
enif_raise_exception.

1 files changed, 41 insertions, 22 deletions

diff --git a/erts/emulator/beam/erl_nif.c b/erts/emulator/beam/erl_nif.c
index 36da6519f7..8c222a6db7 100644
--- a/erts/emulator/beam/erl_nif.c
+++ b/erts/emulator/beam/erl_nif.c
@@ -737,14 +737,20 @@ Eterm enif_make_sub_binary(ErlNifEnv* env, ERL_NIF_TERM bin_term,
 
 Eterm enif_make_badarg(ErlNifEnv* env)
 {
+    return enif_raise_exception(env, am_badarg);
+}
+
+Eterm enif_raise_exception(ErlNifEnv* env, ERL_NIF_TERM reason)
+{
     env->exception_thrown = 1;
-    BIF_ERROR(env->proc, BADARG);
+    env->proc->fvalue = reason;
+    BIF_ERROR(env->proc, EXC_ERROR);
 }
 
 int enif_has_pending_exception(ErlNifEnv* env, ERL_NIF_TERM* reason)
 {
     if (env->exception_thrown && reason != NULL) {
-	*reason = am_badarg;
+	*reason = env->proc->fvalue;
     }
     return env->exception_thrown;
 }
@@ -1541,12 +1547,13 @@ int enif_consume_timeslice(ErlNifEnv* env, int percent)
  * NIF exports need a few more items than the Export struct provides,
  * including the erl_module_nif* and a NIF function pointer, so the
  * NifExport below adds those. The Export member must be first in the
- * struct. The saved_mfa, saved_argc, nif_level, alloced_argv_sz and argv
- * members are used to track the MFA and arguments of the top NIF in case a
- * chain of one or more enif_schedule_nif() calls results in an exception,
- * since in that case the original MFA and registers have to be restored
- * before returning to Erlang to ensure stacktrace information associated
- * with the exception is correct.
+ * struct. The saved_mfa, exception_thrown, saved_argc, rootset_extra, and
+ * rootset members are used to track the MFA, any pending exception, and
+ * arguments of the top NIF in case a chain of one or more
+ * enif_schedule_nif() calls results in an exception, since in that case
+ * the original MFA and registers have to be restored before returning to
+ * Erlang to ensure stacktrace information associated with the exception is
+ * correct.
  */
 typedef ERL_NIF_TERM (*NativeFunPtr)(ErlNifEnv*, int, const ERL_NIF_TERM[]);
 
@@ -1555,25 +1562,28 @@ typedef struct {
     struct erl_module_nif* m;
     NativeFunPtr fp;
     Eterm saved_mfa[3];
+    int exception_thrown;
     int saved_argc;
-    int alloced_argv_sz;
-    Eterm argv[1];
+    int rootset_extra;
+    Eterm rootset[1];
 } NifExport;
 
 /*
  * If a process has saved arguments, they need to be part of the GC
  * rootset. The function below is called from setup_rootset() in
- * erl_gc.c. This function is declared in erl_process.h.
+ * erl_gc.c. This function is declared in erl_process.h. Any exception term
+ * saved in the NifExport is also made part of the GC rootset here; it
+ * always resides in rootset[0].
  */
 int
 erts_setup_nif_gc(Process* proc, Eterm** objv, int* nobj)
 {
     NifExport* ep = (NifExport*) ERTS_PROC_GET_NIF_TRAP_EXPORT(proc);
-    int gc = (ep && ep->saved_argc > 0);
+    int gc = ep && (ep->saved_argc > 0 || ep->rootset[0] != NIL);
 
     if (gc) {
-	*objv = ep->argv;
-	*nobj = ep->saved_argc;
+	*objv = ep->rootset;
+	*nobj = 1 + ep->saved_argc;
     }
     return gc;
 }
@@ -1585,14 +1595,14 @@ static NifExport*
 allocate_nif_sched_data(Process* proc, int argc)
 {
     NifExport* ep;
-    size_t argv_extra, total;
+    size_t total;
     int i;
 
-    argv_extra = argc > 1 ? sizeof(Eterm)*(argc-1) : 0;
-    total = sizeof(NifExport) + argv_extra;
+    total = sizeof(NifExport) + argc*sizeof(Eterm);
     ep = erts_alloc(ERTS_ALC_T_NIF_TRAP_EXPORT, total);
     sys_memset((void*) ep, 0, total);
-    ep->alloced_argv_sz = argc;
+    ep->rootset_extra = argc;
+    ep->rootset[0] = NIL;
     for (i=0; i<ERTS_NUM_CODE_IX; i++) {
 	ep->exp.addressv[i] = &ep->exp.code[3];
     }
@@ -1633,15 +1643,22 @@ init_nif_sched_data(ErlNifEnv* env, NativeFunPtr direct_fp, NativeFunPtr indirec
     ep = (NifExport*) ERTS_PROC_GET_NIF_TRAP_EXPORT(proc);
     if (!ep)
 	ep = allocate_nif_sched_data(proc, argc);
-    else if (need_save && ep->alloced_argv_sz < argc) {
+    else if (need_save && ep->rootset_extra < argc) {
 	NifExport* new_ep = allocate_nif_sched_data(proc, argc);
 	destroy_nif_export(ep);
 	ep = new_ep;
     }
+    if (env->exception_thrown) {
+	ep->exception_thrown = 1;
+	ep->rootset[0] = env->proc->fvalue;
+    } else {
+	ep->exception_thrown = 0;
+	ep->rootset[0] = NIL;
+    }
     ERTS_VBUMP_ALL_REDS(proc);
     for (i = 0; i < argc; i++) {
 	if (need_save)
-	    ep->argv[i] = reg[i];
+	    ep->rootset[i+1] = reg[i];
 	reg[i] = (Eterm) argv[i];
     }
     if (need_save) {
@@ -1677,7 +1694,7 @@ restore_nif_mfa(Process* proc, NifExport* ep, int exception)
     proc->current[2] = ep->saved_mfa[2];
     if (exception)
 	for (i = 0; i < ep->saved_argc; i++)
-	    reg[i] = ep->argv[i];
+	    reg[i] = ep->rootset[i+1];
     ep->saved_argc = 0;
     ep->saved_mfa[0] = THE_NON_VALUE;
 }
@@ -1702,6 +1719,7 @@ dirty_nif_finalizer(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[])
     ASSERT(!ERTS_SCHEDULER_IS_DIRTY(env->proc->scheduler_data));
     ep = (NifExport*) ERTS_PROC_GET_NIF_TRAP_EXPORT(proc);
     ASSERT(ep);
+    ASSERT(!ep->exception_thrown);
     if (ep->fp)
 	restore_nif_mfa(proc, ep, 0);
     return argv[0];
@@ -1719,9 +1737,10 @@ dirty_nif_exception(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[])
     ASSERT(!ERTS_SCHEDULER_IS_DIRTY(env->proc->scheduler_data));
     ep = (NifExport*) ERTS_PROC_GET_NIF_TRAP_EXPORT(proc);
     ASSERT(ep);
+    ASSERT(ep->exception_thrown);
     if (ep->fp)
 	restore_nif_mfa(proc, ep, 1);
-    return enif_make_badarg(env);
+    return enif_raise_exception(env, ep->rootset[0]);
 }
 
 /*