Merge pull request #654 from ReactiveCocoa/anders/locks

Always use error checking pthread mutex.

Author: mdiep

CHANGELOG.md

@@ -2,6 +2,8 @@
 
 *Please add new entries at the top.*
 
+1. When unfair locks from libplatform are unavailable, ReactiveSwift now fallbacks to error checking Pthread mutexes instead of the default. Mitigations regarding issues with `pthread_mutex_trylock` have also been applied. (#654, kudos to @andersio)
+1. Fix some documentation errors about Carthage usage (#655)
 1. [CocoaPods] CocoaPods 1.4.0 is the minimum required version. (#651, kudos to @ikesyo)
 1. `<~` bindings now works with optional left-hand-side operands. (#642, kudos to @andersio and @Ankit-Aggarwal)
 
@@ -13,8 +15,6 @@
    nilTarget <~ notifications.map { $0.count }
    ```
 
-1. Fix some documentation errors about Carthage usage (#655)
-
 # 4.0.0-rc.2
 
 1. Support Swift 4.2 (Xcode 10) (#644, kudos to @ikesyo) 

Sources/Atomic.swift

@@ -155,13 +155,7 @@ internal class Lock {
 				attr.deallocate()
 			}
 
-			// Darwin pthread for 32-bit ARM somehow returns `EAGAIN` when
-			// using `trylock` on a `PTHREAD_MUTEX_ERRORCHECK` mutex.
-			#if DEBUG && !arch(arm)
 			pthread_mutexattr_settype(attr, Int32(recursive ? PTHREAD_MUTEX_RECURSIVE : PTHREAD_MUTEX_ERRORCHECK))
-			#else
-			pthread_mutexattr_settype(attr, Int32(recursive ? PTHREAD_MUTEX_RECURSIVE : PTHREAD_MUTEX_NORMAL))
-			#endif
 
 			let status = pthread_mutex_init(_lock, attr)
 			assert(status == 0, "Unexpected pthread mutex error code: \(status)")
@@ -184,7 +178,7 @@ internal class Lock {
 			switch status {
 			case 0:
 				return true
-			case EBUSY:
+			case EBUSY, EAGAIN:
 				return false
 			default:
 				assertionFailure("Unexpected pthread mutex error code: \(status)")