accept fileno-having objects for GIL-less capture

README.md

@@ -59,13 +59,22 @@ with pipes(logger, stderr=STDOUT):
     call_some_c_function()
 ```
 
+Forward C-level output to a file (avoids GIL issues with a background thread, new in 3.1):
+
+```python
+from wurlitzer import pipes, STDOUT
+
+with open("log.txt", "ab") as f, pipes(f, stderr=STDOUT):
+    blocking_gil_holding_function()
+```
+
 Or even simpler, enable it as an IPython extension:
 
 ```
 %load_ext wurlitzer
 ```
 
-To forward all C-level output to IPython during execution.
+To forward all C-level output to IPython (e.g. Jupyter cell output) during execution.
 
 ## Acknowledgments
 

test.py

@@ -206,3 +206,39 @@ def test_log_pipes(caplog):
         # check 'stream' extra
         assert record.stream
         assert record.name == "wurlitzer." + record.stream
+
+
+def test_two_file_pipes(tmpdir):
+
+    test_stdout = tmpdir / "stdout.txt"
+    test_stderr = tmpdir / "stderr.txt"
+
+    with test_stdout.open("ab") as stdout_f, test_stderr.open("ab") as stderr_f:
+        w = Wurlitzer(stdout_f, stderr_f)
+        with w:
+            assert w.thread is None
+            printf("some stdout")
+            printf_err("some stderr")
+
+    with test_stdout.open() as f:
+        assert f.read() == "some stdout\n"
+    with test_stderr.open() as f:
+        assert f.read() == "some stderr\n"
+
+
+def test_one_file_pipe(tmpdir):
+
+    test_stdout = tmpdir / "stdout.txt"
+
+    with test_stdout.open("ab") as stdout_f:
+        stderr = io.StringIO()
+        w = Wurlitzer(stdout_f, stderr)
+        with w as (stdout, stderr):
+            assert w.thread is not None
+            printf("some stdout")
+            printf_err("some stderr")
+        assert not w.thread.is_alive()
+
+    with test_stdout.open() as f:
+        assert f.read() == "some stdout\n"
+    assert stderr.getvalue() == "some stderr\n"

wurlitzer.py

@@ -210,6 +210,17 @@ def _setup_pipe(self, name):
         save_fd = os.dup(real_fd)
         self._save_fds[name] = save_fd
 
+        try:
+            capture_fd = getattr(self, "_" + name).fileno()
+        except Exception:
+            pass
+        else:
+            # if it has a fileno(),
+            # dup directly to capture file,
+            # no pipes needed
+            dup2(capture_fd, real_fd)
+            return None
+
         pipe_out, pipe_in = os.pipe()
         # set max pipe buffer size (linux only)
         if self._bufsize:
@@ -272,19 +283,32 @@ def __enter__(self):
         self._flush()
         # setup handle
         self._setup_handle()
-        self._control_r, self._control_w = os.pipe()
 
         # create pipe for stdout
-        pipes = [self._control_r]
-        names = {self._control_r: 'control'}
+        pipes = []
+        names = {}
         if self._stdout:
             pipe = self._setup_pipe('stdout')
-            pipes.append(pipe)
-            names[pipe] = 'stdout'
+            if pipe:
+                pipes.append(pipe)
+                names[pipe] = 'stdout'
         if self._stderr:
             pipe = self._setup_pipe('stderr')
-            pipes.append(pipe)
-            names[pipe] = 'stderr'
+            if pipe:
+                pipes.append(pipe)
+                names[pipe] = 'stderr'
+
+        if not pipes:
+            # no pipes to handle (e.g. direct FD capture)
+            # so no forwarder thread needed
+            self.thread = None
+            return self.handle
+
+        # setup forwarder thread
+
+        self._control_r, self._control_w = os.pipe()
+        pipes.append(self._control_r)
+        names[self._control_r] = "control"
 
         # flush pipes in a background thread to avoid blocking
         # the reader thread when the buffer is full
@@ -366,11 +390,11 @@ def forwarder():
     def __exit__(self, exc_type, exc_value, traceback):
         # flush before exiting
         self._flush()
-
-        # signal output is complete on control pipe
-        os.write(self._control_w, b'\1')
-        self.thread.join()
-        os.close(self._control_w)
+        if self.thread:
+            # signal output is complete on control pipe
+            os.write(self._control_w, b'\1')
+            self.thread.join()
+            os.close(self._control_w)
 
         # restore original state
         for name, real_fd in self._real_fds.items():