daemon: ipc to log pid from the child (#10058)

* daemon: ipc to log pid from the child

* fix tests to use pid

* also test for updater/analytics keyword

dvc/daemon.py

@@ -96,32 +96,39 @@ def _fork_process() -> int:
     return pid
 
 
-def _posix_detached_subprocess(args: Sequence[str], **kwargs) -> Optional[int]:
+def _posix_detached_subprocess(args: Sequence[str], **kwargs) -> int:
     # double fork and execute a subprocess so that there are no zombies
+    read_end, write_end = os.pipe()
     pid = _fork_process()
     if pid > 0:  # in parent
-        return None
+        os.close(write_end)
+        pid_str = os.read(read_end, 32).decode("utf8")
+        os.close(read_end)
+        return int(pid_str)
 
     proc = subprocess.Popen(
         args,
         shell=False,  # noqa: S603 # nosec B603
         close_fds=True,
         **kwargs,
     )
+    os.close(read_end)
+    os.write(write_end, str(proc.pid).encode("utf8"))
+    os.close(write_end)
+
     exit_code = proc.wait()
     os._exit(exit_code)
 
 
-def _detached_subprocess(args: Sequence[str], **kwargs) -> Optional[int]:
+def _detached_subprocess(args: Sequence[str], **kwargs) -> int:
     """Run in a detached subprocess."""
     kwargs.setdefault("stdin", subprocess.DEVNULL)
     kwargs.setdefault("stdout", subprocess.DEVNULL)
     kwargs.setdefault("stderr", subprocess.DEVNULL)
 
     if os.name == "nt":
         return _win_detached_subprocess(args, **kwargs)
-    _posix_detached_subprocess(args, **kwargs)
-    return None
+    return _posix_detached_subprocess(args, **kwargs)
 
 
 def _map_log_level_to_flag() -> Optional[str]:
@@ -145,7 +152,7 @@ def _spawn(
     executable: Optional[Union[str, List[str]]] = None,
     env: Optional[Mapping[str, str]] = None,
     output_file: Optional[str] = None,
-) -> Optional[int]:
+) -> int:
     file: "ContextManager[Any]" = nullcontext()
     kwargs = {}
     if output_file:
@@ -177,4 +184,4 @@ def daemonize(args: List[str], executable: Union[None, str, List[str]] = None) -
 
     logger.debug("Trying to spawn %r", args)
     pid = _spawn(args, executable, env, output_file=env.get(DVC_DAEMON_LOGFILE))
-    logger.debug("Spawned %r%s", args, f" with pid {pid}" if pid else "")
+    logger.debug("Spawned %r with pid %s", args, pid)

tests/func/test_daemon.py

@@ -3,14 +3,14 @@
 import re
 import subprocess
 import sys
-import time
 from collections import defaultdict
 from contextlib import contextmanager
 from http.server import HTTPServer, SimpleHTTPRequestHandler
 from pathlib import Path
 from threading import Thread
 from typing import Dict, Iterator
 
+import psutil
 import pytest
 
 from dvc import version_tuple
@@ -82,16 +82,6 @@ def server():
         yield httpd
 
 
-def retry_until(pred, timeout):
-    timeout_ns = timeout * 1e9
-    start = time.perf_counter_ns()
-    while time.perf_counter_ns() - start < timeout_ns:
-        if pred():
-            return
-        time.sleep(0.01)
-    raise RuntimeError(f"timed out after {timeout}s")
-
-
 def test_analytics(tmp_path, server):
     addr = server.server_address
     logfile = tmp_path / "logfile"
@@ -110,18 +100,17 @@ def test_analytics(tmp_path, server):
         text=True,
     )
 
-    pattern = r".*Saving analytics report to (.*)"
-    for line in output.splitlines():
-        if match := re.search(pattern, line):
-            report_file = match.group(1).strip()
-            break
-    else:
-        raise AssertionError("no match for the report file")
-
-    # wait until the file disappears
-    retry_until(lambda: not os.path.exists(report_file), 10)
-    # wait till the daemon exits
-    retry_until(lambda: "exiting with 0" in logfile.read_text(encoding="utf8"), 5)
+    match = re.search(r".*Saving analytics report to (.*)", output, flags=re.M)
+    assert match, "no match for the report file"
+    report_file = match.group(1).strip()
+
+    match = re.search(r".*Spawned .*analytics.* with pid (.*)", output, flags=re.M)
+    assert match, "no match for the pid"
+    pid = int(match.group(1).strip())
+
+    psutil.Process(pid).wait(timeout=10)
+    assert not os.path.exists(report_file)
+    assert f"Process {pid} exiting with 0" in logfile.read_text(encoding="utf8")
     assert server.RequestHandlerClass.hits == {"POST": 1}
 
 
@@ -139,20 +128,21 @@ def test_updater(tmp_dir, dvc, server):
     env.pop("DVC_TEST", None)
     env.pop("CI", None)
 
-    subprocess.check_output(
+    output = subprocess.check_output(
         [*_get_dvc_args(), "version", "-vv"],
         env=env,
         text=True,
     )
 
-    updater_file = Path(dvc.tmp_dir) / Updater.UPDATER_FILE
+    match = re.search(r".*Spawned .*updater.* with pid (.*)", output, flags=re.M)
+    assert match, "no match for the pid"
+    pid = int(match.group(1).strip())
 
-    # wait until the updater file appears
-    retry_until(updater_file.is_file, 10)
-    # wait till the daemon exits
-    retry_until(lambda: "exiting with 0" in logfile.read_text(encoding="utf8"), 5)
+    psutil.Process(pid).wait(timeout=10)
+    assert f"Process {pid} exiting with 0" in logfile.read_text(encoding="utf8")
     assert server.RequestHandlerClass.hits == {"GET": 1}
     # check that the file is saved correctly
+    updater_file = Path(dvc.tmp_dir) / Updater.UPDATER_FILE
     assert json.loads(updater_file.read_text(encoding="utf8")) == UPDATER_INFO