Fix regression in 2.10 that caused printing to stdout/stderr in FileType plugins to not work when running using calibre-debug -g in a windows console

src/calibre/utils/ipc/pool.py

@@ -12,7 +12,7 @@ from collections import namedtuple
 from Queue import Queue
 
 from calibre import detect_ncpus, as_unicode, prints
-from calibre.constants import iswindows
+from calibre.constants import iswindows, DEBUG
 from calibre.ptempfile import PersistentTemporaryFile
 from calibre.utils import join_with_timeout
 from calibre.utils.ipc import eintr_retry_call
@@ -26,9 +26,28 @@ File = namedtuple('File', 'name')
 MAX_SIZE = 30 * 1024 * 1024  # max size of data to send over the connection (old versions of windows cannot handle arbitrary data lengths)
 
 worker_kwargs = {'stdout':None}
-if iswindows and getattr(sys, 'gui_app', False):
-    from calibre.utils.ipc.launch import windows_null_file
-    worker_kwargs['stdout'] = worker_kwargs['stderr'] = windows_null_file
+get_stdout_from_child = False
+
+if iswindows:
+    # The windows console cannot show output from child processes
+    # created with CREATE_NO_WINDOW, so the stdout/stderr file handles
+    # the child process inherits will be broken. Similarly, windows GUI apps
+    # have no usable stdout/stderr file handles. In both these cases, redirect
+    # the child's stdout/stderr to NUL. If we are running in calibre-debug -g,
+    # then redirect to PIPE and read from PIPE and print to our stdout.
+    # Note that when running via the "Restart in debug mode" action, stdout is
+    # not a console (its already redirected to a log file), so no redirection
+    # is required.
+    if getattr(sys, 'gui_app', False) or getattr(sys.stdout, 'isatty', lambda : False)():
+        if DEBUG:
+            # We are running in a windows console with calibre-debug -g
+            import subprocess
+            get_stdout_from_child = True
+            worker_kwargs['stdout'] = subprocess.PIPE
+            worker_kwargs['stderr'] = subprocess.STDOUT
+        else:
+            from calibre.utils.ipc.launch import windows_null_file
+            worker_kwargs['stdout'] = worker_kwargs['stderr'] = windows_null_file
 
 class Failure(Exception):
 
@@ -44,6 +63,10 @@ class Worker(object):
         self.process, self.conn = p, conn
         self.events = events
         self.name = name or ''
+        if get_stdout_from_child:
+            t = Thread(target=self.get_stdout, name='PoolWorkerGetOutput-'+self.name)
+            t.daemon = True
+            t.start()
 
     def __call__(self, job):
         eintr_retry_call(self.conn.send_bytes, cPickle.dumps(job, -1))
@@ -66,6 +89,22 @@ class Worker(object):
     def set_common_data(self, data):
         eintr_retry_call(self.conn.send_bytes, data)
 
+    def get_stdout(self):
+        import time
+        while self.process.poll() is None:
+            try:
+                raw = self.process.stdout.read(1)
+                if raw:
+                    try:
+                        sys.stdout.write(raw)
+                    except EnvironmentError:
+                        pass
+                else:
+                    time.sleep(0.1)
+            except (EOFError, EnvironmentError):
+                break
+
+
 class Pool(Thread):
 
     daemon = True
@@ -339,6 +378,9 @@ def run_main(func):
     with closing(Client(address, authkey=key)) as conn:
         raise SystemExit(func(conn))
 
+def test_write():
+    print ('Printing to stdout in worker')
+
 def test():
     def get_results(pool, ignore_fail=False):
         ans = {}