Add os/sigaction for signal handling.

Also improve interrupts to work better with busy loops
and signals.

examples/sigaction.janet

@@ -0,0 +1,10 @@
+(defn action []
+  (print "Handled SIGHUP!")
+  (flush))
+
+(defn main [_]
+  # Set the interrupt-interpreter argument to `true` to allow
+  # interrupting the busy loop `(forever)`. By default, will not
+  # interrupt the interpreter.
+  (os/sigaction :hup action true)
+  (forever))

src/core/ev.c

@@ -562,6 +562,7 @@ void janet_ev_init_common(void) {
     janet_vm.tq_capacity = 0;
     janet_table_init_raw(&janet_vm.threaded_abstracts, 0);
     janet_table_init_raw(&janet_vm.active_tasks, 0);
+    janet_table_init_raw(&janet_vm.signal_handlers, 0);
     janet_rng_seed(&janet_vm.ev_rng, 0);
 #ifndef JANET_WINDOWS
     pthread_attr_init(&janet_vm.new_thread_attr);
@@ -577,6 +578,7 @@ void janet_ev_deinit_common(void) {
     janet_vm.listeners = NULL;
     janet_table_deinit(&janet_vm.threaded_abstracts);
     janet_table_deinit(&janet_vm.active_tasks);
+    janet_table_deinit(&janet_vm.signal_handlers);
 #ifndef JANET_WINDOWS
     pthread_attr_destroy(&janet_vm.new_thread_attr);
 #endif
@@ -1290,6 +1292,33 @@ int janet_loop_done(void) {
              janet_vm.extra_listeners);
 }
 
+static void janet_loop1_poll(void) {
+    /* Poll for events */
+    if (janet_vm.listener_count || janet_vm.tq_count || janet_vm.extra_listeners) {
+        JanetTimeout to;
+        memset(&to, 0, sizeof(to));
+        int has_timeout;
+        /* Drop timeouts that are no longer needed */
+        while ((has_timeout = peek_timeout(&to))) {
+            if (to.curr_fiber != NULL) {
+                if (!janet_fiber_can_resume(to.curr_fiber)) {
+                    janet_table_remove(&janet_vm.active_tasks, janet_wrap_fiber(to.curr_fiber));
+                    pop_timeout(0);
+                    continue;
+                }
+            } else if (to.fiber->sched_id != to.sched_id) {
+                pop_timeout(0);
+                continue;
+            }
+            break;
+        }
+        /* Run polling implementation only if pending timeouts or pending events */
+        if (janet_vm.tq_count || janet_vm.listener_count || janet_vm.extra_listeners) {
+            janet_loop1_impl(has_timeout, to.when);
+        }
+    }
+}
+
 JanetFiber *janet_loop1(void) {
     /* Schedule expired timers */
     JanetTimeout to;
@@ -1347,30 +1376,7 @@ JanetFiber *janet_loop1(void) {
         }
     }
 
-    /* Poll for events */
-    if (janet_vm.listener_count || janet_vm.tq_count || janet_vm.extra_listeners) {
-        JanetTimeout to;
-        memset(&to, 0, sizeof(to));
-        int has_timeout;
-        /* Drop timeouts that are no longer needed */
-        while ((has_timeout = peek_timeout(&to))) {
-            if (to.curr_fiber != NULL) {
-                if (!janet_fiber_can_resume(to.curr_fiber)) {
-                    janet_table_remove(&janet_vm.active_tasks, janet_wrap_fiber(to.curr_fiber));
-                    pop_timeout(0);
-                    continue;
-                }
-            } else if (to.fiber->sched_id != to.sched_id) {
-                pop_timeout(0);
-                continue;
-            }
-            break;
-        }
-        /* Run polling implementation only if pending timeouts or pending events */
-        if (janet_vm.tq_count || janet_vm.listener_count || janet_vm.extra_listeners) {
-            janet_loop1_impl(has_timeout, to.when);
-        }
-    }
+    janet_loop1_poll();
 
     /* No fiber was interrupted */
     return NULL;
@@ -1391,6 +1397,12 @@ void janet_loop(void) {
     while (!janet_loop_done()) {
         JanetFiber *interrupted_fiber = janet_loop1();
         if (NULL != interrupted_fiber) {
+            /* Allow an extra poll before rescheduling to allow posted events to be handled
+             * before entering a possibly infinite, blocking loop. */
+            Janet x = janet_wrap_fiber(interrupted_fiber);
+            janet_gcroot(x);
+            janet_loop1_poll();
+            janet_gcunroot(x);
             janet_schedule(interrupted_fiber, janet_wrap_nil());
         }
     }

src/core/os.c

@@ -706,6 +706,18 @@ static const struct keyword_signal signal_keywords[] = {
 #endif
     {NULL, 0},
 };
+
+static int get_signal_kw(const Janet *argv, int32_t n) {
+    JanetKeyword signal_kw = janet_getkeyword(argv, n);
+    const struct keyword_signal *ptr = signal_keywords;
+    while (ptr->keyword) {
+        if (!janet_cstrcmp(signal_kw, ptr->keyword)) {
+            return ptr->signal;
+        }
+        ptr++;
+    }
+    janet_panicf("undefined signal %v", argv[n]);
+}
 #endif
 
 JANET_CORE_FN(os_proc_kill,
@@ -731,18 +743,7 @@ JANET_CORE_FN(os_proc_kill,
 #else
     int signal = -1;
     if (argc == 3) {
-        JanetKeyword signal_kw = janet_getkeyword(argv, 2);
-        const struct keyword_signal *ptr = signal_keywords;
-        while (ptr->keyword) {
-            if (!janet_cstrcmp(signal_kw, ptr->keyword)) {
-                signal = ptr->signal;
-                break;
-            }
-            ptr++;
-        }
-        if (signal == -1) {
-            janet_panic("undefined signal");
-        }
+        signal = get_signal_kw(argv, 2);
     }
     int status = kill(proc->pid, signal == -1 ? SIGKILL : signal);
     if (status) {
@@ -803,6 +804,89 @@ static void close_handle(JanetHandle handle) {
 #endif
 }
 
+#ifdef JANET_EV
+
+#ifndef JANET_WINDOWS
+static void janet_signal_callback(JanetEVGenericMessage msg) {
+    int sig = msg.tag;
+    Janet handlerv = janet_table_get(&janet_vm.signal_handlers, janet_wrap_integer(sig));
+    if (!janet_checktype(handlerv, JANET_FUNCTION)) {
+        /* Let another thread/process try to handle this */
+        sigset_t set;
+        sigemptyset(&set);
+        sigaddset(&set, sig);
+        sigprocmask(SIG_BLOCK, &set, NULL);
+        raise(sig);
+        return;
+    }
+    JanetFunction *handler = janet_unwrap_function(handlerv);
+    JanetFiber *fiber = janet_fiber(handler, 64, 0, NULL);
+    janet_schedule(fiber, janet_wrap_nil());
+    if (msg.argi) {
+        janet_ev_dec_refcount();
+    }
+}
+
+static void janet_signal_trampoline_no_interrupt(int sig) {
+    /* Do not interact with global janet state here except for janet_ev_post_event, unsafe! */
+    JanetEVGenericMessage msg;
+    memset(&msg, 0, sizeof(msg));
+    msg.tag = sig;
+    janet_ev_post_event(&janet_vm, janet_signal_callback, msg);
+}
+
+static void janet_signal_trampoline(int sig) {
+    /* Do not interact with global janet state here except for janet_ev_post_event, unsafe! */
+    JanetEVGenericMessage msg;
+    memset(&msg, 0, sizeof(msg));
+    msg.tag = sig;
+    msg.argi = 1;
+    janet_ev_post_event(&janet_vm, janet_signal_callback, msg);
+    janet_ev_inc_refcount();
+    janet_interpreter_interrupt(NULL);
+}
+#endif
+
+JANET_CORE_FN(os_sigaction,
+              "(os/sigaction which &opt handler interrupt-interpreter)",
+              "Add a signal handler for a given action. Use nil for the `handler` argument to remove a signal handler.") {
+    janet_arity(argc, 1, 3);
+#ifdef JANET_WINDOWS
+    janet_panic("unsupported on this platform");
+#else
+    /* TODO - per thread signal masks */
+    int rc;
+    int sig = get_signal_kw(argv, 0);
+    JanetFunction *handler = janet_optfunction(argv, argc, 1, NULL);
+    int can_interrupt = janet_optboolean(argv, argc, 2, 0);
+    Janet oldhandler = janet_table_get(&janet_vm.signal_handlers, janet_wrap_integer(sig));
+    if (!janet_checktype(oldhandler, JANET_NIL)) {
+        janet_gcunroot(oldhandler);
+    }
+    if (NULL != handler) {
+        Janet handlerv = janet_wrap_function(handler);
+        janet_gcroot(handlerv);
+        janet_table_put(&janet_vm.signal_handlers, janet_wrap_integer(sig), handlerv);
+    } else {
+        janet_table_put(&janet_vm.signal_handlers, janet_wrap_integer(sig), janet_wrap_nil());
+    }
+    struct sigaction action;
+    sigset_t mask;
+    sigfillset(&mask);
+    memset(&action, 0, sizeof(action));
+    if (can_interrupt) {
+        action.sa_handler = janet_signal_trampoline;
+    } else {
+        action.sa_handler = janet_signal_trampoline_no_interrupt;
+    }
+    action.sa_mask = mask;
+    RETRY_EINTR(rc, sigaction(sig, &action, NULL));
+    return janet_wrap_nil();
+#endif
+}
+
+#endif
+
 /* Create piped file for os/execute and os/spawn. Need to be careful that we mark
    the error flag if we can't create pipe and don't leak handles. *handle will be cleaned
    up by the calling function. If everything goes well, *handle is owned by the calling function,
@@ -2536,6 +2620,7 @@ void janet_lib_os(JanetTable *env) {
 #ifdef JANET_EV
         JANET_CORE_REG("os/open", os_open), /* fs read and write */
         JANET_CORE_REG("os/pipe", os_pipe),
+        JANET_CORE_REG("os/sigaction", os_sigaction),
 #endif
 #endif
         JANET_REG_END

src/core/state.h

@@ -89,7 +89,7 @@ struct JanetVM {
 
     /* If this flag is true, suspend on function calls and backwards jumps.
      * When this occurs, this flag will be reset to 0. */
-    int auto_suspend;
+    volatile int auto_suspend;
 
     /* The current running fiber on the current thread.
      * Set and unset by functions in vm.c */
@@ -160,6 +160,7 @@ struct JanetVM {
     size_t extra_listeners;
     JanetTable threaded_abstracts; /* All abstract types that can be shared between threads (used in this thread) */
     JanetTable active_tasks; /* All possibly live task fibers - used just for tracking */
+    JanetTable signal_handlers;
 #ifdef JANET_WINDOWS
     void **iocp;
 #elif defined(JANET_EV_EPOLL)

src/core/vm.c

@@ -800,13 +800,13 @@ static JanetSignal run_vm(JanetFiber *fiber, Janet in) {
 
     VM_OP(JOP_JUMP)
     pc += DS;
-    vm_maybe_auto_suspend(DS < 0);
+    vm_maybe_auto_suspend(DS <= 0);
     vm_next();
 
     VM_OP(JOP_JUMP_IF)
     if (janet_truthy(stack[A])) {
         pc += ES;
-        vm_maybe_auto_suspend(ES < 0);
+        vm_maybe_auto_suspend(ES <= 0);
     } else {
         pc++;
     }
@@ -817,14 +817,14 @@ static JanetSignal run_vm(JanetFiber *fiber, Janet in) {
         pc++;
     } else {
         pc += ES;
-        vm_maybe_auto_suspend(ES < 0);
+        vm_maybe_auto_suspend(ES <= 0);
     }
     vm_next();
 
     VM_OP(JOP_JUMP_IF_NIL)
     if (janet_checktype(stack[A], JANET_NIL)) {
         pc += ES;
-        vm_maybe_auto_suspend(ES < 0);
+        vm_maybe_auto_suspend(ES <= 0);
     } else {
         pc++;
     }
@@ -835,7 +835,7 @@ static JanetSignal run_vm(JanetFiber *fiber, Janet in) {
         pc++;
     } else {
         pc += ES;
-        vm_maybe_auto_suspend(ES < 0);
+        vm_maybe_auto_suspend(ES <= 0);
     }
     vm_next();