Fix process polling exit code

src/basic/unix.cpp

@@ -356,7 +356,6 @@ Process SpawnProcess(String command_line, String working_dir, String write_stdin
     }
 
 
-    process.is_valid = true;
     plat->child_stdout_read = stdout_desc[PIPE_READ];
     plat->stdin_write = stdin_desc[PIPE_WRITE];
 
@@ -365,8 +364,7 @@ Process SpawnProcess(String command_line, String working_dir, String write_stdin
         CloseStdin(&process);
     }
 
-
-
+    process.is_valid = true;
     return process;
 }
 
@@ -377,12 +375,14 @@ bool IsValid(Process *process) {
     }
 
     int status = 0;
-    pid_t result = waitpid(plat->pid, &status, WNOHANG);
-    if (result >= 0) {
-        if (WIFSIGNALED(status) || WIFEXITED(status)) {
-            process->exit_code = WEXITSTATUS(status);
-            return false;
-        }
+    pollfd p = {};
+    p.fd = plat->child_stdout_read;
+    p.events = POLLRDHUP | POLLERR | POLLHUP | POLLNVAL;
+    int res = poll(&p, 1, 0);
+    if (res > 0) {
+        pid_t result = waitpid(plat->pid, &status, 0);
+        process->exit_code = WEXITSTATUS(status);
+        return false;
     }
 
     return true;
@@ -406,7 +406,7 @@ String PollStdout(Allocator allocator, Process *process, bool force_read) {
     p.fd = plat->child_stdout_read;
     p.events = POLLIN;
     int res = poll(&p, 1, 0);
-    if (res == 1 || force_read) {
+    if (res > 0 || force_read) {
         result.len = read(plat->child_stdout_read, result.data, 4 * 4096);
     }
     return result;