From 66264fe5730943576b847077dadf5e4531d4beb1 Mon Sep 17 00:00:00 2001
From: Frederick Yin <fkfd@fkfd.me>
Date: Wed, 2 Feb 2022 11:15:09 +0800
Subject: Adapt core to new db

---
 jimbrella/lockfile.py | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)
 create mode 100644 jimbrella/lockfile.py

(limited to 'jimbrella/lockfile.py')

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
-- 
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