src/DbLock.bend source

src/DbLock.bend on the hub · documented module

import Baseimport ./DurableError.bend as DurableErrorimport ./DbLockPolicy.bend as Policy# Owns the open LOCK file until release.type Lock is Type:  Lock{file: File}# Builds the stable LOCK path for a database directory.def lock_path(path: String) -> String:  path ++ "/LOCK"def DbLock.try_lock(file: File) -> IO(File & Result<&1, &1, U32 & String, Unit>):  import "./effs/db_lock.c"  import "./effs/db_lock.js"def DbLock.try_unlock(file: File) -> IO(File & Result<&1, &1, U32 & String, Unit>):  import "./effs/db_unlock.c"  import "./effs/db_unlock.js"# Classifies a failure to open the LOCK file.def open_failed(error: U32 & String, operation: String, path: String) -> IO(Result<&1, &1, DurableError.Error, Lock>):  match error:    case (code, message):      IO.pure(Result<&1, &1, DurableError.Error, Lock>,        Fail{Policy.classify_lock_error(code, message, operation, path)})# Closes the file and classifies a failed lock attempt.def lock_failed(  file: File,  error: U32 & String,  operation: String,  path: String) -> IO(Result<&1, &1, DurableError.Error, Lock>):  match error:    case (code, message):      do IO<Result<&1, &1, DurableError.Error, Lock>>:        _closed : Unit <- File.close(file)        return Fail{Policy.classify_lock_error(code, message, operation, path)}# Returns an owned lock on success or closes the failed handle.def lock_result(  pair: File & Result<&1, &1, U32 & String, Unit>,  operation: String,  path: String) -> IO(Result<&1, &1, DurableError.Error, Lock>):  match pair:    case (file, Fail{error}):      lock_failed(file, error, operation, path)    case (file, Done{Unit{}}):      IO.pure(Result<&1, &1, DurableError.Error, Lock>, Done{Lock{file}})# Attempts the nonblocking OS lock on the open file.def lock_file(file: File, operation: String, path: String) -> IO(Result<&1, &1, DurableError.Error, Lock>):  do IO<Result<&1, &1, DurableError.Error, Lock>>:    pair : File & Result<&1, &1, U32 & String, Unit> <- DbLock.try_lock(file)    lock_result(pair, operation, path)# Locks the opened file or classifies its open error.def opened(  result: Result<&1, &1, U32 & String, File>,  operation: String,  path: String) -> IO(Result<&1, &1, DurableError.Error, Lock>):  match result:    case Fail{error}:      open_failed(error, operation, path)    case Done{file}:      lock_file(file, operation, path)# Opens the stable LOCK file and acquires its OS lock.def acquire(+path: String, operation: String) -> IO(Result<&1, &1, DurableError.Error, Lock>):  do IO<Result<&1, &1, DurableError.Error, Lock>>:    result : Result<&1, &1, U32 & String, File> <- File.open(lock_path(path), "a")    opened(result, operation, path)# Closes the file and preserves the unlock error.def release_failed(  file: File,  error: U32 & String,  operation: String,  path: String) -> IO(Result<&1, &1, DurableError.Error, Unit>):  match error:    case (code, message):      do IO<Result<&1, &1, DurableError.Error, Unit>>:        _closed : Unit <- File.close(file)        return Fail{DurableError.classify_open(DurableError.OpenHostFailure{code, message}, operation, path)}# Closes the file after a successful unlock.def release_succeeded(file: File) -> IO(Result<&1, &1, DurableError.Error, Unit>):  do IO<Result<&1, &1, DurableError.Error, Unit>>:    _closed : Unit <- File.close(file)    return Done{Unit{}}# Closes the file after either unlock result.def released(  pair: File & Result<&1, &1, U32 & String, Unit>,  operation: String,  path: String) -> IO(Result<&1, &1, DurableError.Error, Unit>):  match pair:    case (file, Fail{error}):      release_failed(file, error, operation, path)    case (file, Done{Unit{}}):      release_succeeded(file)# Unlocks the file and closes it after the result.def unlock_file(file: File, operation: String, path: String) -> IO(Result<&1, &1, DurableError.Error, Unit>):  do IO<Result<&1, &1, DurableError.Error, Unit>>:    pair : File & Result<&1, &1, U32 & String, Unit> <- DbLock.try_unlock(file)    released(pair, operation, path)# Consumes the lock and releases its file handle.def release(lock: Lock, operation: String, path: String) -> IO(Result<&1, &1, DurableError.Error, Unit>):  match lock:    case Lock{file}:      unlock_file(file, operation, path)