Stop using spinlocks #43

Apple engineers have pointed out that OSSpinLocks are vulnerable to live locking
on iOS in cases of priority inversion:

. http://mjtsai.com/blog/2015/12/16/osspinlock-is-unsafe/
. https://lists.swift.org/pipermail/swift-dev/Week-of-Mon-20151214/000372.html

YYModel/NSObject+YYModel.m

@@ -11,7 +11,6 @@
 
 #import "NSObject+YYModel.h"
 #import "YYClassInfo.h"
-#import <libkern/OSAtomic.h>
 #import <objc/message.h>
 
 #define force_inline __inline__ __attribute__((always_inline))
@@ -571,20 +570,20 @@ static force_inline id YYValueForMultiKeys(__unsafe_unretained NSDictionary *dic
     if (!cls) return nil;
     static CFMutableDictionaryRef cache;
     static dispatch_once_t onceToken;
-    static OSSpinLock lock;
+    static dispatch_semaphore_t lock;
     dispatch_once(&onceToken, ^{
         cache = CFDictionaryCreateMutable(CFAllocatorGetDefault(), 0, &kCFTypeDictionaryKeyCallBacks, &kCFTypeDictionaryValueCallBacks);
-        lock = OS_SPINLOCK_INIT;
+        lock = dispatch_semaphore_create(1);
     });
-    OSSpinLockLock(&lock);
+    dispatch_semaphore_wait(lock, DISPATCH_TIME_FOREVER);
     _YYModelMeta *meta = CFDictionaryGetValue(cache, (__bridge const void *)(cls));
-    OSSpinLockUnlock(&lock);
+    dispatch_semaphore_signal(lock);
     if (!meta) {
         meta = [[_YYModelMeta alloc] initWithClass:cls];
         if (meta) {
-            OSSpinLockLock(&lock);
+            dispatch_semaphore_wait(lock, DISPATCH_TIME_FOREVER);
             CFDictionarySetValue(cache, (__bridge const void *)(cls), (__bridge const void *)(meta));
-            OSSpinLockUnlock(&lock);
+            dispatch_semaphore_signal(lock);
         }
     }
     return meta;

YYModel/YYClassInfo.m

@@ -11,7 +11,6 @@
 
 #import "YYClassInfo.h"
 #import <objc/runtime.h>
-#import <libkern/OSAtomic.h>
 
 YYEncodingType YYEncodingGetType(const char *typeEncoding) {
     char *type = (char *)typeEncoding;
@@ -309,24 +308,24 @@ YYEncodingType YYEncodingGetType(const char *typeEncoding) {
     static CFMutableDictionaryRef classCache;
     static CFMutableDictionaryRef metaCache;
     static dispatch_once_t onceToken;
-    static OSSpinLock lock;
+    static dispatch_semaphore_t lock;
     dispatch_once(&onceToken, ^{
         classCache = CFDictionaryCreateMutable(CFAllocatorGetDefault(), 0, &kCFTypeDictionaryKeyCallBacks, &kCFTypeDictionaryValueCallBacks);
         metaCache = CFDictionaryCreateMutable(CFAllocatorGetDefault(), 0, &kCFTypeDictionaryKeyCallBacks, &kCFTypeDictionaryValueCallBacks);
-        lock = OS_SPINLOCK_INIT;
+        lock = dispatch_semaphore_create(1);
     });
-    OSSpinLockLock(&lock);
+    dispatch_semaphore_wait(lock, DISPATCH_TIME_FOREVER);
     YYClassInfo *info = CFDictionaryGetValue(class_isMetaClass(cls) ? metaCache : classCache, (__bridge const void *)(cls));
     if (info && info->_needUpdate) {
         [info _update];
     }
-    OSSpinLockUnlock(&lock);
+    dispatch_semaphore_signal(lock);
     if (!info) {
         info = [[YYClassInfo alloc] initWithClass:cls];
         if (info) {
-            OSSpinLockLock(&lock);
+            dispatch_semaphore_wait(lock, DISPATCH_TIME_FOREVER);
             CFDictionarySetValue(info.isMeta ? metaCache : classCache, (__bridge const void *)(cls), (__bridge const void *)(info));
-            OSSpinLockUnlock(&lock);
+            dispatch_semaphore_signal(lock);
         }
     }
     return info;