RunLoops should be a single instance per their scope

NSRunLoop.mainRunLoop() should return a single object
and it should be the same as NSRunLoop. currentRunLoop() and subsequent calls of both should not create new run loops

Author: phausler

CoreFoundation/Base.subproj/ForSwiftFoundationOnly.h

@@ -177,6 +177,10 @@ struct _NSXMLParserBridge {
                            const unsigned char *SystemID);
 };
 
+struct _NSRunLoop {
+    CFTypeRef (*_new)(CFRunLoopRef rl);
+};
+
 struct _CFSwiftBridge {
     struct _NSObjectBridge NSObject;
     struct _NSArrayBridge NSArray;
@@ -188,6 +192,7 @@ struct _CFSwiftBridge {
     struct _NSStringBridge NSString;
     struct _NSMutableStringBridge NSMutableString;
     struct _NSXMLParserBridge NSXMLParser;
+    struct _NSRunLoop NSRunLoop;
 };
 
 __attribute__((__visibility__("hidden"))) extern struct _CFSwiftBridge __CFSwiftBridge;
@@ -264,6 +269,8 @@ extern void *_CFReallocf(void *ptr, size_t size);
 
 CFHashCode CFStringHashNSString(CFStringRef str);
 
+extern CFTypeRef _CFRunLoopGet2(CFRunLoopRef rl);
+
 extern CFIndex __CFStringEncodeByteStream(CFStringRef string, CFIndex rangeLoc, CFIndex rangeLen, Boolean generatingExternalFile, CFStringEncoding encoding, uint8_t lossByte,  UInt8 * _Nullable buffer, CFIndex max, CFIndex * _Nullable usedBufLen);
 
 typedef	unsigned char __cf_uuid[16];

CoreFoundation/RunLoop.subproj/CFRunLoop.c

@@ -1526,7 +1526,12 @@ CF_PRIVATE void __CFFinalizeRunLoop(uintptr_t data) {
     }
     if (rl && CFRunLoopGetMain() != rl) { // protect against cooperative threads
         if (NULL != rl->_counterpart) {
+#if DEPLOYMENT_RUNTIME_SWIFT
+            extern void swift_release(void *);
+            swift_release((void *)rl->_counterpart);
+#else
             CFRelease(rl->_counterpart);
+#endif
 	    rl->_counterpart = NULL;
         }
 	// purge all sources before deallocation
@@ -1549,6 +1554,12 @@ pthread_t _CFRunLoopGet1(CFRunLoopRef rl) {
 CF_EXPORT CFTypeRef _CFRunLoopGet2(CFRunLoopRef rl) {
     CFTypeRef ret = NULL;
     __CFLock(&loopsLock);
+#if DEPLOYMENT_RUNTIME_SWIFT
+    if (rl->_counterpart == NULL) {
+        CFTypeRef ns = __CFSwiftBridge.NSRunLoop._new(rl); // returns retained so we will claim ownership of that return value by just assigning (the release is balanced in the destruction of the CFRunLoop
+        rl->_counterpart = ns;
+    }
+#endif
     ret = rl->_counterpart;
     __CFUnlock(&loopsLock);
     return ret;

Foundation/NSRunLoop.swift

@@ -12,22 +12,24 @@ import CoreFoundation
 public let NSDefaultRunLoopMode: String = kCFRunLoopDefaultMode._swiftObject
 public let NSRunLoopCommonModes: String = kCFRunLoopCommonModes._swiftObject
 
+internal func _NSRunLoopNew(cf: CFRunLoopRef) -> Unmanaged<AnyObject>! {
+    let rl = Unmanaged<NSRunLoop>.passRetained(NSRunLoop(cfObject: cf))
+    return unsafeBitCast(rl, Unmanaged<AnyObject>.self) // this retain is balanced on the other side of the CF fence
+}
+
 public class NSRunLoop : NSObject {
     internal var _cfRunLoop : CFRunLoopRef!
-    internal static var _mainRunLoop : NSRunLoop = {
-        return NSRunLoop(cfObject: CFRunLoopGetMain())
-    }()
 
     internal init(cfObject : CFRunLoopRef) {
         _cfRunLoop = cfObject
     }
 
     public class func currentRunLoop() -> NSRunLoop {
-        return NSRunLoop(cfObject: CFRunLoopGetCurrent())
+        return _CFRunLoopGet2(CFRunLoopGetCurrent()) as! NSRunLoop
     }
 
     public class func mainRunLoop() -> NSRunLoop {
-        return _mainRunLoop
+        return _CFRunLoopGet2(CFRunLoopGetMain()) as! NSRunLoop
     }
 
     public var currentMode: String? {

Foundation/NSSwiftRuntime.swift

@@ -199,6 +199,8 @@ internal func __CFInitializeSwift() {
     __CFSwiftBridge.NSXMLParser.comment = _NSXMLParserComment
     __CFSwiftBridge.NSXMLParser.externalSubset = _NSXMLParserExternalSubset
 
+    __CFSwiftBridge.NSRunLoop._new = _NSRunLoopNew
+    
     __CFDefaultEightBitStringEncoding = UInt32(kCFStringEncodingUTF8)
 }
 

TestFoundation/TestNSRunLoop.swift

@@ -31,6 +31,18 @@ class TestNSRunLoop : XCTestCase {
         XCTAssertNotNil(mainRunLoop)
         let currentRunLoop = NSRunLoop.currentRunLoop()
         XCTAssertNotNil(currentRunLoop)
+
+        let secondAccessOfMainLoop = NSRunLoop.mainRunLoop()
+        XCTAssertEqual(mainRunLoop, secondAccessOfMainLoop, "fetching the main loop a second time should be equal")
+        XCTAssertTrue(mainRunLoop === secondAccessOfMainLoop, "fetching the main loop a second time should be identical")
+        
+        let secondAccessOfCurrentLoop = NSRunLoop.currentRunLoop()
+        XCTAssertEqual(currentRunLoop, secondAccessOfCurrentLoop, "fetching the current loop a second time should be equal")
+        XCTAssertTrue(currentRunLoop === secondAccessOfCurrentLoop, "fetching the current loop a second time should be identical")
+        
+        // We can assume that the tests will be run on the main run loop
+        // so the current loop should be the main loop
+        XCTAssertEqual(mainRunLoop, currentRunLoop, "the current run loop should be the main loop")
     }
 
     func test_runLoopRunMode() {
@@ -70,5 +82,4 @@ class TestNSRunLoop : XCTestCase {
 
         XCTAssertLessThan(abs(timerTickInterval - expectedTimeInterval), 0.01)
     }
-    
 }