1	import Base
2	import ./DurableError.bend as DurableError
3	import ./DbLockPolicy.bend as Policy
4	
5	# Owns the open LOCK file until release.
6	type Lock is Type:
7	  Lock{file: File}
8	
9	# Builds the stable LOCK path for a database directory.
10	def lock_path(path: String) -> String:
11	  path ++ "/LOCK"
12	
13	def DbLock.try_lock(file: File) -> IO(File & Result<&1, &1, U32 & String, Unit>):
14	  import "./effs/db_lock.c"
15	  import "./effs/db_lock.js"
16	
17	def DbLock.try_unlock(file: File) -> IO(File & Result<&1, &1, U32 & String, Unit>):
18	  import "./effs/db_unlock.c"
19	  import "./effs/db_unlock.js"
20	
21	# Classifies a failure to open the LOCK file.
22	def open_failed(error: U32 & String, operation: String, path: String) -> IO(Result<&1, &1, DurableError.Error, Lock>):
23	  match error:
24	    case (code, message):
25	      IO.pure(Result<&1, &1, DurableError.Error, Lock>,
26	        Fail{Policy.classify_lock_error(code, message, operation, path)})
27	
28	# Closes the file and classifies a failed lock attempt.
29	def lock_failed(
30	  file: File,
31	  error: U32 & String,
32	  operation: String,
33	  path: String
34	) -> IO(Result<&1, &1, DurableError.Error, Lock>):
35	  match error:
36	    case (code, message):
37	      do IO<Result<&1, &1, DurableError.Error, Lock>>:
38	        _closed : Unit <- File.close(file)
39	        return Fail{Policy.classify_lock_error(code, message, operation, path)}
40	
41	# Returns an owned lock on success or closes the failed handle.
42	def lock_result(
43	  pair: File & Result<&1, &1, U32 & String, Unit>,
44	  operation: String,
45	  path: String
46	) -> IO(Result<&1, &1, DurableError.Error, Lock>):
47	  match pair:
48	    case (file, Fail{error}):
49	      lock_failed(file, error, operation, path)
50	    case (file, Done{Unit{}}):
51	      IO.pure(Result<&1, &1, DurableError.Error, Lock>, Done{Lock{file}})
52	
53	# Attempts the nonblocking OS lock on the open file.
54	def lock_file(file: File, operation: String, path: String) -> IO(Result<&1, &1, DurableError.Error, Lock>):
55	  do IO<Result<&1, &1, DurableError.Error, Lock>>:
56	    pair : File & Result<&1, &1, U32 & String, Unit> <- DbLock.try_lock(file)
57	    lock_result(pair, operation, path)
58	
59	# Locks the opened file or classifies its open error.
60	def opened(
61	  result: Result<&1, &1, U32 & String, File>,
62	  operation: String,
63	  path: String
64	) -> IO(Result<&1, &1, DurableError.Error, Lock>):
65	  match result:
66	    case Fail{error}:
67	      open_failed(error, operation, path)
68	    case Done{file}:
69	      lock_file(file, operation, path)
70	
71	# Opens the stable LOCK file and acquires its OS lock.
72	def acquire(+path: String, operation: String) -> IO(Result<&1, &1, DurableError.Error, Lock>):
73	  do IO<Result<&1, &1, DurableError.Error, Lock>>:
74	    result : Result<&1, &1, U32 & String, File> <- File.open(lock_path(path), "a")
75	    opened(result, operation, path)
76	
77	# Closes the file and preserves the unlock error.
78	def release_failed(
79	  file: File,
80	  error: U32 & String,
81	  operation: String,
82	  path: String
83	) -> IO(Result<&1, &1, DurableError.Error, Unit>):
84	  match error:
85	    case (code, message):
86	      do IO<Result<&1, &1, DurableError.Error, Unit>>:
87	        _closed : Unit <- File.close(file)
88	        return Fail{DurableError.classify_open(DurableError.OpenHostFailure{code, message}, operation, path)}
89	
90	# Closes the file after a successful unlock.
91	def release_succeeded(file: File) -> IO(Result<&1, &1, DurableError.Error, Unit>):
92	  do IO<Result<&1, &1, DurableError.Error, Unit>>:
93	    _closed : Unit <- File.close(file)
94	    return Done{Unit{}}
95	
96	# Closes the file after either unlock result.
97	def released(
98	  pair: File & Result<&1, &1, U32 & String, Unit>,
99	  operation: String,
100	  path: String
101	) -> IO(Result<&1, &1, DurableError.Error, Unit>):
102	  match pair:
103	    case (file, Fail{error}):
104	      release_failed(file, error, operation, path)
105	    case (file, Done{Unit{}}):
106	      release_succeeded(file)
107	
108	# Unlocks the file and closes it after the result.
109	def unlock_file(file: File, operation: String, path: String) -> IO(Result<&1, &1, DurableError.Error, Unit>):
110	  do IO<Result<&1, &1, DurableError.Error, Unit>>:
111	    pair : File & Result<&1, &1, U32 & String, Unit> <- DbLock.try_unlock(file)
112	    released(pair, operation, path)
113	
114	# Consumes the lock and releases its file handle.
115	def release(lock: Lock, operation: String, path: String) -> IO(Result<&1, &1, DurableError.Error, Unit>):
116	  match lock:
117	    case Lock{file}:
118	      unlock_file(file, operation, path)