Detect is os_unfair_lock is available at runtime, in order to be able to support older versions of macOS in the same binaries.

Author: guidotack

changelog.in

@@ -72,6 +72,14 @@ Date: TBD
 [DESCRIPTION]
 Changes
 
+[ENTRY]
+Module: support
+What:   change
+Rank:   minor
+[DESCRIPTION]
+Detect is os_unfair_lock is available at runtime, in order to be able
+to support older versions of macOS in the same binaries.
+
 [ENTRY]
 Module: flatzinc
 What:   change

gecode/support/thread.hpp

@@ -108,8 +108,14 @@ namespace Gecode { namespace Support {
     /// Use a simple but more efficient critical section on Windows
     CRITICAL_SECTION w_cs;
 #elif defined(GECODE_THREADS_OSX_UNFAIR)
-    /// Use unfair lock on macOS
-    os_unfair_lock lck;
+    /// Use unfair lock on macOS if available, OSSpinLock on older macOS
+    union {
+      os_unfair_lock unfair_lck;
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wdeprecated-declarations"
+      OSSpinLock spin_lck;
+#pragma clang diagnostic pop
+    } u;
 #elif defined(GECODE_THREADS_PTHREADS)
     /// The Pthread mutex
     pthread_mutex_t p_m;

gecode/support/thread/pthreads.hpp

@@ -45,26 +45,45 @@ namespace Gecode { namespace Support {
 
 #ifdef GECODE_THREADS_OSX_UNFAIR
 
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wdeprecated-declarations"
   /*
   * Mutex
   */
   forceinline
-  Mutex::Mutex(void) : lck(OS_UNFAIR_LOCK_INIT)  {}
+  Mutex::Mutex(void) {
+    if (&os_unfair_lock_lock != NULL)
+      u.unfair_lck = OS_UNFAIR_LOCK_INIT;
+    else
+      u.spin_lck = OS_SPINLOCK_INIT;
+  }
   forceinline void
   Mutex::acquire(void) {
-    os_unfair_lock_lock(&lck);
+    if (&os_unfair_lock_lock != NULL) {
+      os_unfair_lock_lock(&u.unfair_lck);
+    } else {
+      OSSpinLockLock(&u.spin_lck);
+    }
   }
   forceinline bool
   Mutex::tryacquire(void) {
-    return os_unfair_lock_trylock(&lck);
+    if (&os_unfair_lock_trylock != NULL)
+      return os_unfair_lock_trylock(&u.unfair_lck);
+    else
+      return OSSpinLockTry(&u.spin_lck);
   }
   forceinline void
   Mutex::release(void) {
-    os_unfair_lock_unlock(&lck);
+    if (&os_unfair_lock_unlock != NULL)
+      os_unfair_lock_unlock(&u.unfair_lck);
+    else
+      OSSpinLockUnlock(&u.spin_lck);
   }
   forceinline
   Mutex::~Mutex(void) {}
 
+#pragma clang diagnostic pop
+
 #else
 
   /*