feat(ble/ObjC): add countdownlatch impl in ObjC

Signed-off-by: Sacha Froment <sfroment42@gmail.com>

core/network/ble/CountDownLatch.h

@@ -0,0 +1,28 @@
+//
+//  CountDownLatch.h
+//  ble
+//
+//  Created by sacha on 22/11/2018.
+//  Copyright © 2018 berty. All rights reserved.
+//
+
+
+
+#ifndef CountDownLatch_h
+#define CountDownLatch_h
+
+#import <Foundation/Foundation.h>
+
+@interface CountDownLatch : NSObject
+
+@property (nonatomic, assign) int count;
+@property (atomic, readwrite, strong) dispatch_semaphore_t semaphore;
+@property (nonatomic, strong) dispatch_queue_t dispatch_queue;
+
+- (instancetype)init:(int)count;
+- (void)coundDown;
+- (void)await;
+
+@end
+
+#endif

core/network/ble/CountDownLatch.m

@@ -0,0 +1,38 @@
+//
+//  CountDownLatch.m
+//  ble
+//
+//  Created by sacha on 22/11/2018.
+//  Copyright © 2018 berty. All rights reserved.
+//
+
+#import "CountDownLatch.h"
+
+@implementation CountDownLatch
+
+- (instancetype)init:(int)count {
+    if (count < 0) {
+        return nil;
+    }
+
+    self.count = count;
+    self.semaphore = dispatch_semaphore_create(0);
+    self.dispatch_queue = dispatch_queue_create("CountDownLatchQueue", DISPATCH_QUEUE_CONCURRENT);
+    [super self];
+    return self;
+}
+
+- (void)coundDown {
+    dispatch_async(self.dispatch_queue, ^{
+        self.count--;
+        if (self.count == 0) {
+            while (dispatch_semaphore_signal(self.semaphore) != 0) {};
+        }
+    });
+}
+
+- (void)await {
+    dispatch_semaphore_wait(self.semaphore, DISPATCH_TIME_FOREVER);
+}
+
+@end