Wait/retry when cannot delete file on Windows

Author: pkch

mypy/build.py

@@ -901,7 +901,7 @@ def write_cache(id: str, path: str, tree: MypyFile,
             f.write(data_str)
             f.write('\n')
         data_mtime = os.path.getmtime(data_json_tmp)
-        os.replace(data_json_tmp, data_json)
+        util.replace(data_json_tmp, data_json)
         manager.trace("Interface for {} has changed".format(id))
 
     mtime = st.st_mtime
@@ -927,7 +927,7 @@ def write_cache(id: str, path: str, tree: MypyFile,
             json.dump(meta, f, indent=2, sort_keys=True)
         else:
             json.dump(meta, f)
-    os.replace(meta_json_tmp, meta_json)
+    util.replace(meta_json_tmp, meta_json)
 
     return interface_hash
 

mypy/test/testutil.py

@@ -0,0 +1,41 @@
+import sys
+from typing import Type, Callable, List
+import time
+try:
+    import collections.abc as collections_abc
+except ImportError:
+    import collections as collections_abc  # type: ignore # PY32 and earlier
+from unittest import TestCase, main, skipUnless
+from mypy import util
+
+
+def create_bad_function(lag: float, exc: BaseException) -> Callable[[], None]:
+    start_time = time.perf_counter()
+
+    def f() -> None:
+        if time.perf_counter() - start_time < lag:
+            raise exc
+        else:
+            return
+    return f
+
+
+def create_funcs() -> List[Callable[[], None]]:
+
+    def linux_function() -> None: pass
+    windows_function1 = create_bad_function(0.01, PermissionError())
+    windows_function2 = create_bad_function(0.02, FileExistsError())
+    return [windows_function1, windows_function2, linux_function]
+
+
+class WaitRetryTests(TestCase):
+    def test_waitfor(self) -> None:
+        with self.assertRaises(OSError):
+            util.wait_for(create_funcs(), (PermissionError, FileExistsError), 0.01)
+        util.wait_for(create_funcs(), (PermissionError, FileExistsError), 1)
+        with self.assertRaises(FileExistsError):
+            util.wait_for(create_funcs(), (PermissionError,), 0.04)
+
+
+if __name__ == '__main__':
+    main()

mypy/util.py

@@ -2,8 +2,15 @@
 
 import re
 import subprocess
+import os
+import sys
+import math
+import time
+from functools import partial
 from xml.sax.saxutils import escape
-from typing import TypeVar, List, Tuple, Optional, Sequence, Dict
+from typing import (
+    TypeVar, List, Tuple, Optional, Sequence, Dict, Callable, Iterable, Type, Union, AnyStr, cast
+)
 
 
 T = TypeVar('T')
@@ -134,3 +141,54 @@ def id(self, o: object) -> int:
             self.id_map[o] = self.next_id
             self.next_id += 1
         return self.id_map[o]
+
+
+# default timeout is short in case this functions is called individually for many files
+# batch processing results in better performance
+def wait_for(funcs: Iterable[Callable[[], None]],
+             exc: Iterable[Type[BaseException]] = (),
+             timeout: float = 0.1,
+             msg: str = 'file operations') -> None:
+    '''
+    Execute functions in funcs (without arguments)
+    Wait and retry all functions that raised exception that matches exc
+    Increase wait time exponentially, give up after a total wait of timeout seconds
+    Reraises the latest exception seen if timeout exceeded
+    '''
+    exc = tuple(exc)
+    last_exc = None
+    pending = set(funcs)
+    n_iter = max(1, math.ceil(math.log2(timeout / 0.001)))
+    for i in range(n_iter):
+        if not pending:
+            return
+        # last wait is ~ timeout/2, so that total wait ~ timeout
+        wait = timeout / 2 ** (n_iter - i)
+        failed = set()
+        for func in pending:
+            try:
+                func()
+            except exc as e:
+                last_exc = e
+                failed.add(func)
+        pending = failed
+        time.sleep(wait)
+    sys.stderr.write('timed out waiting for {}'.format(msg))
+    raise last_exc
+
+
+if sys.version_info >= (3, 6):
+    PathType = Union[AnyStr, os.PathLike]
+else:
+    PathType = AnyStr
+
+
+def _replace(src: PathType, dest: PathType) -> None:
+    repl = cast(Callable[[], None], partial(os.replace, src, dest))
+    wait_for([repl], (OSError,), 0.1)
+
+
+if sys.platform.startswith("win"):
+    replace = _replace
+else:
+    replace = os.replace

runtests.py

@@ -215,6 +215,7 @@ def add_imports(driver: Driver) -> None:
     'testdiff',
     'testfinegrained',
     'testmerge',
+    'testutil',
 ]]