From ef7129f45d1239e10d63e03eec93a2776ac3fea1 Mon Sep 17 00:00:00 2001
From: Calvin Rose <calsrose@gmail.com>
Date: Thu, 18 Nov 2021 19:03:08 -0600
Subject: [PATCH] Address #874 - Call waitpid on waiter thread with WNOWAIT.

This doesn't destory the pid until the original thread decides to
call waitpid again. Since the pid is exposed in the C API and now
in the Janet API, we don't want to destroy it until we are ready.
---
 src/core/os.c | 26 +++++++++++++++-----------
 1 file changed, 15 insertions(+), 11 deletions(-)

diff --git a/src/core/os.c b/src/core/os.c
index 8c75eac0..752e1dd1 100644
--- a/src/core/os.c
+++ b/src/core/os.c
@@ -415,17 +415,8 @@ static JanetEVGenericMessage janet_proc_wait_subr(JanetEVGenericMessage args) {
     pid_t result;
     int status = 0;
     do {
-        result = waitpid(proc->pid, &status, 0);
+        result = waitpid(proc->pid, &status, WNOWAIT);
     } while (result == -1 && errno == EINTR);
-    /* Use POSIX shell semantics for interpreting signals */
-    if (WIFEXITED(status)) {
-        status = WEXITSTATUS(status);
-    } else if (WIFSTOPPED(status)) {
-        status = WSTOPSIG(status) + 128;
-    } else {
-        status = WTERMSIG(status) + 128;
-    }
-    args.argi = status;
     return args;
 }
 
@@ -434,9 +425,22 @@ static JanetEVGenericMessage janet_proc_wait_subr(JanetEVGenericMessage args) {
 /* Callback that is called in main thread when subroutine completes. */
 static void janet_proc_wait_cb(JanetEVGenericMessage args) {
     janet_ev_dec_refcount();
-    int status = args.argi;
     JanetProc *proc = (JanetProc *) args.argp;
     if (NULL != proc) {
+        /* Wait again without NOWAIT.
+         * Use POSIX shell semantics for interpreting signals */
+        int status = 0;
+        pid_t result;
+        do {
+            result = waitpid(proc->pid, &status, 0);
+        } while (result == -1 && errno == EINTR);
+        if (WIFEXITED(status)) {
+            status = WEXITSTATUS(status);
+        } else if (WIFSTOPPED(status)) {
+            status = WSTOPSIG(status) + 128;
+        } else {
+            status = WTERMSIG(status) + 128;
+        }
         proc->return_code = (int32_t) status;
         proc->flags |= JANET_PROC_WAITED;
         proc->flags &= ~JANET_PROC_WAITING;