From 1c17d02f57a3f559ecab63ee5d81ae33eb6210e3 Mon Sep 17 00:00:00 2001
From: "Mr. Outis" <mroutis@protonmail.com>
Date: Fri, 31 Jan 2020 16:08:04 -0600
Subject: [PATCH 1/2] rwlock: include actionable in error message

Fix: #3164
---
 dvc/rwlock.py | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/dvc/rwlock.py b/dvc/rwlock.py
index d805bcd55a..871b23a545 100644
--- a/dvc/rwlock.py
+++ b/dvc/rwlock.py
@@ -73,8 +73,11 @@ def _check_no_writers(lock, info, path_infos):
             continue
 
         raise LockError(
-            "'{}' is busy, it is being written to by:\n{}".format(
-                str(path_info), _infos_to_str(writers)
+            "'{path}' is busy, it is being written to by:\n{process}"
+            "\n\n"
+            "If there's no process with such PID, you can manually remove"
+            "'.dvc/tmp/rwlock' and try again.".format(
+                path=str(path_info), process=_infos_to_str(writers)
             )
         )
 
@@ -91,8 +94,11 @@ def _check_no_readers(lock, info, path_infos):
             continue
 
         raise LockError(
-            "'{}' is busy, it is being read by:\n{}".format(
-                str(path_info), _infos_to_str(readers)
+            "'{path}' is busy, it is being read by:\n{process}"
+            "\n\n"
+            "If there's no process with such PID, you can manually remove"
+            "'.dvc/tmp/rwlock' and try again.".format(
+                path=str(path_info), process=_infos_to_str(readers)
             )
         )
 

From e6ed5cc6cf766a47a5b824671c7de049eb6a980d Mon Sep 17 00:00:00 2001
From: "Mr. Outis" <mroutis@protonmail.com>
Date: Tue, 4 Feb 2020 18:05:21 -0600
Subject: [PATCH 2/2] rwlock: check blockers on a single method

---
 dvc/rwlock.py | 53 +++++++++++++++++----------------------------------
 1 file changed, 17 insertions(+), 36 deletions(-)

diff --git a/dvc/rwlock.py b/dvc/rwlock.py
index 871b23a545..ce452d0a0c 100644
--- a/dvc/rwlock.py
+++ b/dvc/rwlock.py
@@ -5,7 +5,6 @@
 from contextlib import contextmanager
 
 from voluptuous import Schema, Invalid
-from funcy.py3 import lmap, lfilter, lmapcat
 
 from .exceptions import DvcException
 from .lock import LockError
@@ -61,44 +60,25 @@ def _infos_to_str(infos):
     )
 
 
-def _check_no_writers(lock, info, path_infos):
-    for path_info in path_infos:
-        blocking_urls = lfilter(path_info.overlaps, lock["write"])
-        if not blocking_urls:
-            continue
-
-        writers = lmap(lock["write"].get, blocking_urls)
-        writers = lfilter(lambda i: info != i, writers)
-        if not writers:
-            continue
-
-        raise LockError(
-            "'{path}' is busy, it is being written to by:\n{process}"
-            "\n\n"
-            "If there's no process with such PID, you can manually remove"
-            "'.dvc/tmp/rwlock' and try again.".format(
-                path=str(path_info), process=_infos_to_str(writers)
-            )
-        )
+def _check_blockers(lock, info, *, mode, waiters):
+    for path_info in waiters:
+        blockers = [
+            info
+            for path, infos in lock[mode].items()
+            if path_info.overlaps(path)
+            if info not in (infos if type(infos) is list else [infos])
+        ]
 
-
-def _check_no_readers(lock, info, path_infos):
-    for path_info in path_infos:
-        blocking_urls = lfilter(path_info.overlaps, lock["read"])
-        if not blocking_urls:
-            continue
-
-        readers = lmapcat(lock["read"].get, blocking_urls)
-        readers = lfilter(lambda i: info != i, readers)
-        if not readers:
+        if not blockers:
             continue
 
         raise LockError(
-            "'{path}' is busy, it is being read by:\n{process}"
-            "\n\n"
-            "If there's no process with such PID, you can manually remove"
+            "'{path}' is busy, it is being blocked by:\n"
+            "{blockers}\n"
+            "\n"
+            "If there are no processes with such PIDs, you can manually remove"
             "'.dvc/tmp/rwlock' and try again.".format(
-                path=str(path_info), process=_infos_to_str(readers)
+                path=str(path_info), blockers=_infos_to_str(blockers)
             )
         )
 
@@ -177,8 +157,9 @@ def rwlock(tmp_dir, cmd, read, write):
     info = {"pid": os.getpid(), "cmd": cmd}
 
     with _edit_rwlock(tmp_dir) as lock:
-        _check_no_writers(lock, info, read + write)
-        _check_no_readers(lock, info, write)
+
+        _check_blockers(lock, info, mode="write", waiters=read + write)
+        _check_blockers(lock, info, mode="read", waiters=write)
 
         rchanges = _acquire_read(lock, info, read)
         wchanges = _acquire_write(lock, info, write)