Add GTMSynchronizationAsserts.h/m and a unit test file.

These macros allow code to assert being in or not in a @sync-protected section,
which is important when calling across methods or calling out to other classes
or callbacks.

1 files changed, 124 insertions, 0 deletions

diff --git a/DebugUtils/GTMSynchronizationAsserts.h b/DebugUtils/GTMSynchronizationAsserts.h
new file mode 100644
index 0000000..b026565
--- /dev/null
+++ b/DebugUtils/GTMSynchronizationAsserts.h
@@ -0,0 +1,124 @@
+//
+//  GTMSynchronizationAsserts.h
+//
+//  Copyright 2016 Google Inc.
+//
+//  Licensed under the Apache License, Version 2.0 (the "License"); you may not
+//  use this file except in compliance with the License.  You may obtain a copy
+//  of the License at
+//
+//  http://www.apache.org/licenses/LICENSE-2.0
+//
+//  Unless required by applicable law or agreed to in writing, software
+//  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+//  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
+//  License for the specific language governing permissions and limitations under
+//  the License.
+//
+
+#if !__has_feature(objc_arc)
+#error "This file needs to be compiled with ARC enabled."
+#endif
+
+#import <Foundation/Foundation.h>
+
+#import "GTMDefines.h"  // For _GTMDevAssert.
+
+// Macros to monitor synchronization blocks in debug builds.
+//
+// These report problems using _GTMDevAssert, which may be defined by the
+// project or by GTMDefines.h
+//
+// GTMMonitorSynchronized           Start monitoring a top-level-only @sync scope.
+//                                  Asserts if already inside a monitored @sync scope.
+// GTMMonitorRecursiveSynchronized  Start monitoring a top-level or recursive @sync
+//                                  scope.
+// GTMCheckSynchronized             Assert that the current execution is inside a monitored @sync
+//                                  scope.
+// GTMCheckNotSynchronized          Assert that the current execution is not inside a monitored
+//                                  @sync scope.
+//
+// Example usage:
+//
+// - (void)myExternalMethod {
+//   @synchronized(self) {
+//     GTMMonitorSynchronized(self)
+//
+// - (void)myInternalMethod {
+//   GTMCheckSynchronized(self);
+//
+// - (void)callMyCallbacks {
+//   GTMCheckNotSynchronized(self);
+//
+// GTMCheckNotSynchronized is available for verifying the code isn't
+// in a deadlockable @sync state, important when posting notifications and
+// invoking callbacks.
+//
+// Don't use GTMCheckNotSynchronized immediately before a @sync scope; the
+// normal recursiveness check of GTMMonitorSynchronized can catch those.
+
+#if DEBUG
+
+  #define __GTMMonitorSynchronizedVariableInner(varname, counter) \
+      varname ## counter
+  #define __GTMMonitorSynchronizedVariable(varname, counter)      \
+      __GTMMonitorSynchronizedVariableInner(varname, counter)
+
+  #define GTMMonitorSynchronized(obj)                                           \
+      NS_VALID_UNTIL_END_OF_SCOPE id                                            \
+        __GTMMonitorSynchronizedVariable(__monitor, __COUNTER__) =              \
+        [[GTMSyncMonitorInternal alloc] initWithSynchronizationObject:obj       \
+                                                    allowRecursive:NO           \
+                                                     functionName:__func__]
+
+  #define GTMMonitorRecursiveSynchronized(obj)                                  \
+      NS_VALID_UNTIL_END_OF_SCOPE id                                            \
+        __GTMMonitorSynchronizedVariable(__monitor, __COUNTER__) =              \
+        [[GTMSyncMonitorInternal alloc] initWithSynchronizationObject:obj       \
+                                                    allowRecursive:YES          \
+                                                     functionName:__func__]
+
+  #define GTMCheckSynchronized(obj) {                                           \
+      _GTMDevAssert(                                                            \
+          [GTMSyncMonitorInternal functionsHoldingSynchronizationOnObject:obj], \
+          @"GTMCheckSynchronized(" #obj ") failed: not sync'd"                  \
+          @" on " #obj " in %s. Call stack:\n%@",                               \
+          __func__, [NSThread callStackSymbols]);                               \
+      }
+
+  #define GTMCheckNotSynchronized(obj) {                                       \
+      _GTMDevAssert(                                                           \
+        ![GTMSyncMonitorInternal functionsHoldingSynchronizationOnObject:obj], \
+        @"GTMCheckNotSynchronized(" #obj ") failed: was sync'd"                \
+        @" on " #obj " in %s by %@. Call stack:\n%@", __func__,                \
+        [GTMSyncMonitorInternal functionsHoldingSynchronizationOnObject:obj],  \
+        [NSThread callStackSymbols]);                                          \
+      }
+
+// GTMSyncMonitorInternal is a private class that keeps track of the
+// beginning and end of synchronized scopes, relying on ARC to release
+// it at the end of a scope.
+//
+// This class should not be used directly, but only via the
+// GTMMonitorSynchronized macro.
+@interface GTMSyncMonitorInternal : NSObject {
+  NSValue *_objectKey;        // The synchronize target object.
+  const char *_functionName;  // The function containing the monitored sync block.
+}
+
+- (instancetype)initWithSynchronizationObject:(id)object
+                               allowRecursive:(BOOL)allowRecursive
+                                 functionName:(const char *)functionName;
+// Return the names of the functions that hold sync on the object, or nil if none.
++ (NSArray *)functionsHoldingSynchronizationOnObject:(id)object;
+@end
+
+#else
+
+  // !DEBUG
+  #define GTMMonitorSynchronized(obj) do { } while (0)
+  #define GTMMonitorRecursiveSynchronized(obj) do { } while (0)
+  #define GTMCheckSynchronized(obj) do { } while (0)
+  #define GTMCheckNotSynchronized(obj) do { } while (0)
+
+#endif  // DEBUG