Implement locking for update/bulkchange process

Avoid the possibility of these two clashing especially when multiple
branches are being used.

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>

layerindex/bulkchange.py

@@ -215,6 +215,12 @@ def main():
     fetchdir = settings.LAYER_FETCH_DIR
     bitbakepath = os.path.join(fetchdir, 'bitbake')
 
+    lockfn = os.path.join(fetchdir, "layerindex.lock")
+    lockfile = utils.lock_file(lockfn)
+    if not lockfile:
+        sys.stderr.write("Layer index lock timeout expired\n")
+        sys.exit(1)
+    try:
         (tinfoil, tempdir) = recipeparse.init_parser(settings, branch, bitbakepath, True)
 
         changeset = get_changeset(sys.argv[1])
@@ -223,6 +229,9 @@ def main():
             sys.exit(1)
 
         outp = generate_patches(tinfoil, fetchdir, changeset, sys.argv[2])
+    finally:
+        utils.unlock_file(lockfile)
+
     if outp:
         print outp
     else:

layerindex/update.py

@@ -174,6 +174,12 @@ def main():
     fetchedrepos = []
     failedrepos = []
 
+    lockfn = os.path.join(fetchdir, "layerindex.lock")
+    lockfile = utils.lock_file(lockfn)
+    if not lockfile:
+        logger.error("Layer index lock timeout expired")
+        sys.exit(1)
+    try:
         bitbakepath = os.path.join(fetchdir, 'bitbake')
 
         if not options.nofetch:
@@ -513,6 +519,9 @@ def main():
             finally:
                 transaction.leave_transaction_management()
 
+    finally:
+        utils.unlock_file(lockfile)
+
     shutil.rmtree(tempdir)
     sys.exit(0)
 

layerindex/utils.py

@@ -9,6 +9,8 @@ import sys
 import os.path
 import subprocess
 import logging
+import time
+import fcntl
 
 def get_branch(branchname):
     from layerindex.models import Branch
@@ -63,3 +65,18 @@ def logger_create(name):
     logger.addHandler(loggerhandler)
     logger.setLevel(logging.INFO)
     return logger
+
+def lock_file(fn):
+    starttime = time.time()
+    while True:
+        lock = open(fn, 'w')
+        try:
+            fcntl.flock(lock, fcntl.LOCK_EX | fcntl.LOCK_NB)
+            return lock
+        except IOError:
+            lock.close()
+            if time.time() - starttime > 30:
+                return None
+
+def unlock_file(lock):
+    fcntl.flock(lock, fcntl.LOCK_UN)