Fixed the subprocess read deadlock

nvflare/app_common/launchers/subprocess_launcher.py

@@ -18,18 +18,70 @@
 from threading import Thread
 from typing import Optional
 
+from nvflare.utils.job_launcher_utils import add_custom_dir_to_path
+
 from nvflare.apis.fl_constant import FLContextKey
 from nvflare.apis.fl_context import FLContext
 from nvflare.apis.shareable import Shareable
 from nvflare.apis.signal import Signal
 from nvflare.app_common.abstract.launcher import Launcher, LauncherRunStatus
 from nvflare.fuel.utils.log_utils import get_obj_logger
-from nvflare.utils.job_launcher_utils import add_custom_dir_to_path
+
+
+def get_line(buffer: bytearray):
+    """Read a line from the binary buffer. It treats all combinations of \n and \r as line breaks.
+
+    Args:
+        buffer: A binary buffer
+
+    Returns:
+        (line, remaining): Return the first line as str and the remaining buffer.
+        line is None if no newline found
+
+    """
+    size = len(buffer)
+    r = buffer.find(b"\r")
+    if r < 0:
+        r = size + 1
+    n = buffer.find(b"\n")
+    if n < 0:
+        n = size + 1
+    index = min(r, n)
+
+    if index >= size:
+        return None, buffer
+
+    # if \r and \n are adjacent, treat them as one
+    if abs(r - n) == 1:
+        index = index + 1
+
+    line = buffer[:index].decode().rstrip()
+    if index >= size - 1:
+        remaining = bytearray()
+    else:
+        remaining = buffer[index + 1 :]
+    return line, remaining
 
 
 def log_subprocess_output(process, logger):
-    for c in iter(process.stdout.readline, b""):
-        logger.info(c.decode().rstrip())
+
+    buffer = bytearray()
+    while True:
+        chunk = process.stdout.read1(4096)
+        if not chunk:
+            break
+        buffer = buffer + chunk
+
+        while True:
+            line, buffer = get_line(buffer)
+            if line is None:
+                break
+
+            if line:
+                logger.info(line)
+
+    if buffer:
+        logger.info(buffer.decode())
 
 
 class SubprocessLauncher(Launcher):