fix potential leaks and improve comments

Author: Jan Philipp Hafer

test/standalone/childprocess_extrapipe/child.zig

@@ -11,14 +11,14 @@ pub fn main() !void {
     _ = it.next() orelse unreachable; // skip binary name
     const s_handle = it.next() orelse unreachable;
     var file_handle = try std.os.stringToHandle(s_handle);
+    defer std.os.close(file_handle);
 
     // child inherited the handle, so inheritance must be enabled
     const is_inheritable = try std.os.isInheritable(file_handle);
     std.debug.assert(is_inheritable);
 
     try std.os.disableInheritance(file_handle);
     var file_in = std.fs.File{ .handle = file_handle }; // read side of pipe
-    defer file_in.close();
     const file_in_reader = file_in.reader();
     const message = try file_in_reader.readUntilDelimiterAlloc(gpa, '\x17', 20_000);
     defer gpa.free(message);

test/standalone/childprocess_extrapipe/parent.zig

@@ -20,21 +20,21 @@ pub fn main() !void {
     const child_path = it.next() orelse unreachable;
 
     var pipe = try child_process.portablePipe();
-
-    // write read side of pipe to string + add to spawn command
-    var buf: [os.handleCharSize]u8 = comptime [_]u8{0} ** os.handleCharSize;
-    const s_handle = try os.handleToString(pipe[pipe_rd], &buf);
-    var child_proc = ChildProcess.init(
-        &.{ child_path, s_handle },
-        gpa,
-    );
-
-    // enabling of file inheritance directly before and closing directly after spawn
-    // less time to leak => better
+    defer os.close(pipe[pipe_wr]);
+    var child_proc: ChildProcess = undefined;
+    // spawn block ensures read end of pipe always closed + shortly closed after spawn().
     {
-        try os.enableInheritance(pipe[pipe_rd]);
         defer os.close(pipe[pipe_rd]);
 
+        var buf: [os.handleCharSize]u8 = comptime [_]u8{0} ** os.handleCharSize;
+        const s_handle = os.handleToString(pipe[pipe_rd], &buf) catch unreachable;
+        child_proc = ChildProcess.init(
+            &.{ child_path, s_handle },
+            gpa,
+        );
+
+        // less time to leak read end of pipe => better
+        try os.enableInheritance(pipe[pipe_rd]);
         try child_proc.spawn();
     }
 
@@ -43,7 +43,6 @@ pub fn main() !void {
     std.debug.assert(!is_inheritable);
 
     var file_out = std.fs.File{ .handle = pipe[pipe_wr] };
-    defer file_out.close();
     const file_out_writer = file_out.writer();
     try file_out_writer.writeAll("test123\x17"); // ETB = \x17
     const ret_val = try child_proc.wait();