Windows: fix termination of process output redirection (#29923)

The parent thread in the process stdout redirection logic on Windows
was closing a file that was being read in child thread, which lead to
error-based termination of the reader thread. This updates the
interaction to avoid the error.

lib/spack/llnl/util/tty/log.py

@@ -809,19 +809,23 @@ def __enter__(self):
             def background_reader(reader, echo_writer, _kill):
                 # for each line printed to logfile, read it
                 # if echo: write line to user
+                try:
                     while True:
                         is_killed = _kill.wait(.1)
+                        # Flush buffered build output to file
+                        # stdout/err fds refer to log file
                         self.stderr.flush()
                         self.stdout.flush()
+
                         line = reader.readline()
-                    while line:
-                        if self.echo:
-                            self.echo_writer.write('{0}'.format(line.decode()))
-                            self.echo_writer.flush()
-                        line = reader.readline()
+                        if self.echo and line:
+                            echo_writer.write('{0}'.format(line.decode()))
+                            echo_writer.flush()
 
                         if is_killed:
                             break
+                finally:
+                    reader.close()
 
             self._active = True
             with replace_environment(self.env):
@@ -837,7 +841,6 @@ def __exit__(self, exc_type, exc_val, exc_tb):
             self._ioflag = False
         else:
             self.writer.close()
-            self.reader.close()
             self.echo_writer.flush()
             self.stdout.flush()
             self.stderr.flush()
@@ -853,10 +856,7 @@ def force_echo(self):
         if not self._active:
             raise RuntimeError(
                 "Can't call force_echo() outside log_output region!")
-        try:
-            yield self
-        finally:
-            pass
+        yield
 
 
 def _writer_daemon(stdin_multiprocess_fd, read_multiprocess_fd, write_fd, echo,

lib/spack/spack/main.py

@@ -30,7 +30,7 @@
 import llnl.util.tty as tty
 import llnl.util.tty.colify
 import llnl.util.tty.color as color
-from llnl.util.tty.log import log_output, winlog
+from llnl.util.tty.log import log_output
 
 import spack
 import spack.cmd
@@ -605,11 +605,6 @@ def __call__(self, *argv, **kwargs):
 
         out = StringIO()
         try:
-            if sys.platform == 'win32':
-                with winlog(out):
-                    self.returncode = _invoke_command(
-                        self.command, self.parser, args, unknown)
-            else:
             with log_output(out):
                 self.returncode = _invoke_command(
                     self.command, self.parser, args, unknown)