Adapt core to new db

1 files changed, 33 insertions, 0 deletions

diff --git a/jimbrella/lockfile.py b/jimbrella/lockfile.py
new file mode 100644
index 0000000..987f0e3
--- /dev/null
+++ b/jimbrella/lockfile.py
@@ -0,0 +1,33 @@
+import os
+
+
+class Lockfile:
+    """Prevent unwanted concurrency for file I/O.
+
+    For a file named "<file>", create or remove a lockfile named "<file>.lock".
+
+    When a process is modifying the file, call `lock(). When the modification
+    is done, call `unlock()`.
+    """
+
+    def __init__(self, filepath):
+        self.filepath = str(filepath)
+        self.lockpath = self.filepath + ".lock"
+
+    def lock(self):
+        """Continue attempting to lock until locked."""
+        locked = False
+        while not locked:
+            try:
+                f = open(self.lockpath, "x")
+                f.close()
+                locked = True
+            except FileExistsError:
+                continue
+
+    def unlock(self):
+        """Remove lockfile."""
+        try:
+            os.remove(self.lockpath)
+        except FileNotFoundError:
+            return