Use libpthread primitives for OpenBSD mutexes.

stdlib/public/Synchronization/CMakeLists.txt

@@ -80,6 +80,13 @@ set(SWIFT_SYNCHRONIZATION_WINDOWS_SOURCES
   Mutex/WindowsImpl.swift
 )
 
+# OpenBSD sources
+
+set(SWIFT_SYNCHRONIZATION_OPENBSD_SOURCES
+  Mutex/Mutex.swift
+  Mutex/OpenBSDImpl.swift
+)
+
 set(SWIFT_SYNCHRNOIZATION_SWIFT_FLAGS
   ${SWIFT_STANDARD_LIBRARY_SWIFT_FLAGS}
   "-enable-builtin-module"
@@ -115,6 +122,8 @@ add_swift_target_library(swiftSynchronization ${SWIFT_STDLIB_LIBRARY_BUILD_TYPES
     ${SWIFT_SYNCHRONIZATION_WINDOWS_SOURCES}
   SWIFT_SOURCES_DEPENDS_FREEBSD
     ${SWIFT_SYNCHRONIZATION_FREEBSD_SOURCES}
+  SWIFT_SOURCES_DEPENDS_OPENBSD
+    ${SWIFT_SYNCHRONIZATION_OPENBSD_SOURCES}
   SWIFT_SOURCES_DEPENDS_FREESTANDING
     Mutex/MutexUnavailable.swift
 
@@ -140,6 +149,8 @@ add_swift_target_library(swiftSynchronization ${SWIFT_STDLIB_LIBRARY_BUILD_TYPES
     WinSDK
   SWIFT_MODULE_DEPENDS_FREEBSD
     Glibc
+  SWIFT_MODULE_DEPENDS_OPENBSD
+    Glibc
 
   SWIFT_COMPILE_FLAGS
     ${SWIFT_SYNCHRNOIZATION_SWIFT_FLAGS}

stdlib/public/Synchronization/Mutex/OpenBSDImpl.swift

@@ -0,0 +1,58 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift Atomics open source project
+//
+// Copyright (c) 2024 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+import Glibc
+
+@available(SwiftStdlib 6.0, *)
+@frozen
+@_staticExclusiveOnly
+public struct _MutexHandle: ~Copyable {
+  @usableFromInline
+  let value: _Cell<pthread_mutex_t?>
+
+  @available(SwiftStdlib 6.0, *)
+  @_alwaysEmitIntoClient
+  @_transparent
+  public init() {
+    var mx = pthread_mutex_t(bitPattern: 0)
+    pthread_mutex_init(&mx, nil)
+    value = _Cell(mx)
+  }
+
+  @available(SwiftStdlib 6.0, *)
+  @_alwaysEmitIntoClient
+  @_transparent
+  internal borrowing func _lock() {
+    pthread_mutex_lock(value._address)
+  }
+
+  @available(SwiftStdlib 6.0, *)
+  @_alwaysEmitIntoClient
+  @_transparent
+  internal borrowing func _tryLock() -> Bool {
+    pthread_mutex_trylock(value._address) != 0
+  }
+
+  @available(SwiftStdlib 6.0, *)
+  @_alwaysEmitIntoClient
+  @_transparent
+  internal borrowing func _unlock() {
+    pthread_mutex_unlock(value._address)
+  }
+
+  @available(SwiftStdlib 6.0, *)
+  @_alwaysEmitIntoClient
+  @_transparent
+  deinit {
+    pthread_mutex_destroy(value._address)
+  }
+}