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lock.swift
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lock.swift
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//===----------------------------------------------------------------------===//
//
// This source file is part of the SwiftNIO open source project
//
// Copyright (c) 2017-2018 Apple Inc. and the SwiftNIO project authors
// Licensed under Apache License v2.0
//
// See LICENSE.txt for license information
// See CONTRIBUTORS.txt for the list of SwiftNIO project authors
//
// SPDX-License-Identifier: Apache-2.0
//
//===----------------------------------------------------------------------===//
#if os(macOS) || os(iOS) || os(watchOS) || os(tvOS)
import Darwin
#elseif os(Windows)
import ucrt
import WinSDK
#else
import Glibc
#endif
/// A threading lock based on `libpthread` instead of `libdispatch`.
///
/// This object provides a lock on top of a single `pthread_mutex_t`. This kind
/// of lock is safe to use with `libpthread`-based threading models, such as the
/// one used by NIO.
public final class Lock {
#if os(Windows)
fileprivate let mutex: UnsafeMutablePointer<SRWLOCK> =
UnsafeMutablePointer.allocate(capacity: 1)
#else
fileprivate let mutex: UnsafeMutablePointer<pthread_mutex_t> =
UnsafeMutablePointer.allocate(capacity: 1)
#endif
/// Create a new lock.
public init() {
#if os(Windows)
InitializeSRWLock(self.mutex)
#else
var attr = pthread_mutexattr_t()
pthread_mutexattr_init(&attr);
pthread_mutexattr_settype(&attr, .init(PTHREAD_MUTEX_ERRORCHECK));
let err = pthread_mutex_init(self.mutex, &attr)
precondition(err == 0, "\(#function) failed in pthread_mutex with error \(err)")
#endif
}
deinit {
#if os(Windows)
// mutexes do not need to be explicitly destroyed
#else
let err = pthread_mutex_destroy(self.mutex)
precondition(err == 0, "\(#function) failed in pthread_mutex with error \(err)")
#endif
mutex.deallocate()
}
/// Acquire the lock.
///
/// Whenever possible, consider using `withLock` instead of this method and
/// `unlock`, to simplify lock handling.
public func lock() {
#if os(Windows)
AcquireSRWLockExclusive(self.mutex)
#else
let err = pthread_mutex_lock(self.mutex)
precondition(err == 0, "\(#function) failed in pthread_mutex with error \(err)")
#endif
}
/// Release the lock.
///
/// Whenver possible, consider using `withLock` instead of this method and
/// `lock`, to simplify lock handling.
public func unlock() {
#if os(Windows)
ReleaseSRWLockExclusive(self.mutex)
#else
let err = pthread_mutex_unlock(self.mutex)
precondition(err == 0, "\(#function) failed in pthread_mutex with error \(err)")
#endif
}
}
extension Lock {
/// Acquire the lock for the duration of the given block.
///
/// This convenience method should be preferred to `lock` and `unlock` in
/// most situations, as it ensures that the lock will be released regardless
/// of how `body` exits.
///
/// - Parameter body: The block to execute while holding the lock.
/// - Returns: The value returned by the block.
@inlinable
public func withLock<T>(_ body: () throws -> T) rethrows -> T {
self.lock()
defer {
self.unlock()
}
return try body()
}
// specialise Void return (for performance)
@inlinable
public func withLockVoid(_ body: () throws -> Void) rethrows -> Void {
try self.withLock(body)
}
}
/// A `Lock` with a built-in state variable.
///
/// This class provides a convenience addition to `Lock`: it provides the ability to wait
/// until the state variable is set to a specific value to acquire the lock.
public final class ConditionLock<T: Equatable> {
private var _value: T
private let mutex: Lock
#if os(Windows)
private let cond: UnsafeMutablePointer<CONDITION_VARIABLE> =
UnsafeMutablePointer.allocate(capacity: 1)
#else
private let cond: UnsafeMutablePointer<pthread_cond_t> =
UnsafeMutablePointer.allocate(capacity: 1)
#endif
/// Create the lock, and initialize the state variable to `value`.
///
/// - Parameter value: The initial value to give the state variable.
public init(value: T) {
self._value = value
self.mutex = Lock()
#if os(Windows)
InitializeConditionVariable(self.cond)
#else
let err = pthread_cond_init(self.cond, nil)
precondition(err == 0, "\(#function) failed in pthread_cond with error \(err)")
#endif
}
deinit {
#if os(Windows)
// condition variables do not need to be explicitly destroyed
#else
let err = pthread_cond_destroy(self.cond)
precondition(err == 0, "\(#function) failed in pthread_cond with error \(err)")
#endif
self.cond.deallocate()
}
/// Acquire the lock, regardless of the value of the state variable.
public func lock() {
self.mutex.lock()
}
/// Release the lock, regardless of the value of the state variable.
public func unlock() {
self.mutex.unlock()
}
/// The value of the state variable.
///
/// Obtaining the value of the state variable requires acquiring the lock.
/// This means that it is not safe to access this property while holding the
/// lock: it is only safe to use it when not holding it.
public var value: T {
self.lock()
defer {
self.unlock()
}
return self._value
}
/// Acquire the lock when the state variable is equal to `wantedValue`.
///
/// - Parameter wantedValue: The value to wait for the state variable
/// to have before acquiring the lock.
public func lock(whenValue wantedValue: T) {
self.lock()
while true {
if self._value == wantedValue {
break
}
#if os(Windows)
let result = SleepConditionVariableSRW(self.cond, self.mutex.mutex, INFINITE, 0)
precondition(result, "\(#function) failed in SleepConditionVariableSRW with error \(GetLastError())")
#else
let err = pthread_cond_wait(self.cond, self.mutex.mutex)
precondition(err == 0, "\(#function) failed in pthread_cond with error \(err)")
#endif
}
}
/// Acquire the lock when the state variable is equal to `wantedValue`,
/// waiting no more than `timeoutSeconds` seconds.
///
/// - Parameter wantedValue: The value to wait for the state variable
/// to have before acquiring the lock.
/// - Parameter timeoutSeconds: The number of seconds to wait to acquire
/// the lock before giving up.
/// - Returns: `true` if the lock was acquired, `false` if the wait timed out.
public func lock(whenValue wantedValue: T, timeoutSeconds: Double) -> Bool {
precondition(timeoutSeconds >= 0)
#if os(Windows)
var dwMilliseconds: DWORD = DWORD(timeoutSeconds * 1000)
self.lock()
while true {
if self._value == wantedValue {
return true
}
let dwWaitStart = timeGetTime()
if !SleepConditionVariableSRW(self.cond, self.mutex.mutex,
dwMilliseconds, 0) {
let dwError = GetLastError()
if (dwError == ERROR_TIMEOUT) {
self.unlock()
return false
}
fatalError("SleepConditionVariableSRW: \(dwError)")
}
// NOTE: this may be a spurious wakeup, adjust the timeout accordingly
dwMilliseconds = dwMilliseconds - (timeGetTime() - dwWaitStart)
}
#else
let nsecPerSec: Int64 = 1000000000
self.lock()
/* the timeout as a (seconds, nano seconds) pair */
let timeoutNS = Int64(timeoutSeconds * Double(nsecPerSec))
var curTime = timeval()
gettimeofday(&curTime, nil)
let allNSecs: Int64 = timeoutNS + Int64(curTime.tv_usec) * 1000
var timeoutAbs = timespec(tv_sec: curTime.tv_sec + Int((allNSecs / nsecPerSec)),
tv_nsec: Int(allNSecs % nsecPerSec))
assert(timeoutAbs.tv_nsec >= 0 && timeoutAbs.tv_nsec < Int(nsecPerSec))
assert(timeoutAbs.tv_sec >= curTime.tv_sec)
while true {
if self._value == wantedValue {
return true
}
switch pthread_cond_timedwait(self.cond, self.mutex.mutex, &timeoutAbs) {
case 0:
continue
case ETIMEDOUT:
self.unlock()
return false
case let e:
fatalError("caught error \(e) when calling pthread_cond_timedwait")
}
}
#endif
}
/// Release the lock, setting the state variable to `newValue`.
///
/// - Parameter newValue: The value to give to the state variable when we
/// release the lock.
public func unlock(withValue newValue: T) {
self._value = newValue
self.unlock()
#if os(Windows)
WakeAllConditionVariable(self.cond)
#else
let err = pthread_cond_broadcast(self.cond)
precondition(err == 0, "\(#function) failed in pthread_cond with error \(err)")
#endif
}
}