Add portalocker for inter-process lock

trains/utilities/locks/constants.py

@@ -0,0 +1,41 @@
+"""
+Locking constants
+
+Lock types:
+
+- `LOCK_EX` exclusive lock
+- `LOCK_SH` shared lock
+
+Lock flags:
+
+- `LOCK_NB` non-blocking
+
+Manually unlock, only needed internally
+
+- `LOCK_UN` unlock
+"""
+import os
+
+# The actual tests will execute the code anyhow so the following code can
+# safely be ignored from the coverage tests
+if os.name == 'nt':  # pragma: no cover
+    import msvcrt
+
+    LOCK_EX = 0x1  #: exclusive lock
+    LOCK_SH = 0x2  #: shared lock
+    LOCK_NB = 0x4  #: non-blocking
+    LOCK_UN = msvcrt.LK_UNLCK  #: unlock
+
+    LOCKFILE_FAIL_IMMEDIATELY = 1
+    LOCKFILE_EXCLUSIVE_LOCK = 2
+
+elif os.name == 'posix':  # pragma: no cover
+    import fcntl
+
+    LOCK_EX = fcntl.LOCK_EX  #: exclusive lock
+    LOCK_SH = fcntl.LOCK_SH  #: shared lock
+    LOCK_NB = fcntl.LOCK_NB  #: non-blocking
+    LOCK_UN = fcntl.LOCK_UN  #: unlock
+
+else:  # pragma: no cover
+    raise RuntimeError('PortaLocker only defined for nt and posix platforms')