quentin has experienced a glaring race condition in make_rundirs when…

… launching multiple workflows at once.

it's unclear to me why its *so bad* in his situation, but the race condition exists none-the-less
and this PR complicates rundir creation to accept that it might be run multiple times concurrently

parsl/dataflow/errors.py

@@ -63,3 +63,7 @@ def __init__(self, dependent_exceptions_tids: Sequence[Tuple[BaseException, Opti
     def __str__(self) -> str:
         dep_tids = [tid for (exception, tid) in self.dependent_exceptions_tids]
         return "Join failure for task {} with failed join dependencies from tasks {}".format(self.task_id, dep_tids)
+
+
+class RundirCreateError(ParslError):
+    pass

parsl/dataflow/rundirs.py

@@ -1,11 +1,15 @@
 import os
 from glob import glob
 import logging
+import random
+import time
+
+from parsl.dataflow.errors import RundirCreateError
 
 logger = logging.getLogger(__name__)
 
 
-def make_rundir(path: str) -> str:
+def make_rundir(path: str, *, max_tries: int = 3) -> str:
     """When a path has not been specified, make the run directory.
 
     Creates a rundir with the following hierarchy:
@@ -18,23 +22,39 @@ def make_rundir(path: str) -> str:
     Kwargs:
         - path (str): String path to a specific run dir
     """
-    try:
-        if not os.path.exists(path):
-            os.makedirs(path)
-
-        prev_rundirs = glob(os.path.join(path, "[0-9]*[0-9]"))
-
-        current_rundir = os.path.join(path, '000')
-
-        if prev_rundirs:
-            # Since we globbed on files named as 0-9
-            x = sorted([int(os.path.basename(x)) for x in prev_rundirs])[-1]
-            current_rundir = os.path.join(path, '{0:03}'.format(x + 1))
-
-        os.makedirs(current_rundir)
-        logger.debug("Parsl run initializing in rundir: {0}".format(current_rundir))
-        return os.path.abspath(current_rundir)
-
-    except Exception:
-        logger.exception("Failed to create run directory")
-        raise
+    backoff_time_s = 1 + random.random()
+
+    os.makedirs(path, exist_ok=True)
+
+    # try_count is 1-based for human readability
+    try_count = 1
+    while True:
+
+        # Python 3.10 introduces root_dir argument to glob which in future
+        # can be used to simplify this code, something like:
+        #   prev_rundirs = glob("[0-9]*[0-9]", root_dir=path)
+        full_prev_rundirs = glob(os.path.join(path, "[0-9]*[0-9]"))
+        prev_rundirs = [os.path.basename(d) for d in full_prev_rundirs]
+
+        next = max([int(d) for d in prev_rundirs] + [-1]) + 1
+
+        current_rundir = os.path.join(path, '{0:03}'.format(next))
+
+        try:
+            os.makedirs(current_rundir)
+            logger.debug("rundir created: {}", current_rundir)
+            return os.path.abspath(current_rundir)
+        except FileExistsError:
+            logger.warning(f"Could not create rundir {current_rundir} on try {try_count}")
+
+            if try_count >= max_tries:
+                raise
+            else:
+                logger.debug("Backing off {}s", backoff_time_s)
+                time.sleep(backoff_time_s)
+                backoff_time_s *= 2 + random.random()
+                try_count += 1
+
+    # this should never be reached - the above loop should have either returned
+    # or raised an exception on the last try
+    raise RundirCreateError()