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, 93 insertions, 0 deletions

diff --git a/DebugUtils/GTMSynchronizationAsserts.m b/DebugUtils/GTMSynchronizationAsserts.m
new file mode 100644
index 0000000..6c76550
--- /dev/null
+++ b/DebugUtils/GTMSynchronizationAsserts.m
@@ -0,0 +1,93 @@
+//
+//  GTMSyncAsserts.m
+//
+//  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.
+//
+
+#import "GTMSynchronizationAsserts.h"
+
+#if DEBUG
+
+@implementation GTMSyncMonitorInternal
+
+- (instancetype)initWithSynchronizationObject:(id)object
+                               allowRecursive:(BOOL)allowRecursive
+                                 functionName:(const char *)functionName {
+  self = [super init];
+  if (self) {
+    // In the thread's dictionary, we keep a counted set of the names
+    // of functions that are synchronizing on the object.
+    Class threadKey = [GTMSyncMonitorInternal class];
+    _objectKey = [NSValue valueWithNonretainedObject:object];
+    _functionName = functionName;
+
+    NSMutableDictionary *threadDict = [NSThread currentThread].threadDictionary;
+    NSMutableDictionary *counters = threadDict[threadKey];
+    if (counters == nil) {
+      counters = [NSMutableDictionary dictionary];
+      threadDict[(id)threadKey] = counters;
+    }
+    NSCountedSet *functionNamesCounter = counters[_objectKey];
+    NSUInteger numberOfSyncingFunctions = functionNamesCounter.count;
+
+    if (!allowRecursive) {
+      BOOL isTopLevelSyncScope = (numberOfSyncingFunctions == 0);
+      NSArray *stack = [NSThread callStackSymbols];
+      _GTMDevAssert(isTopLevelSyncScope,
+                    @"*** Recursive sync on %@ at %s; previous sync at %@\n%@",
+                    [object class], functionName, functionNamesCounter.allObjects,
+                    [stack subarrayWithRange:NSMakeRange(1, stack.count - 1)]);
+    }
+
+    if (!functionNamesCounter) {
+      functionNamesCounter = [NSCountedSet set];
+      counters[_objectKey] = functionNamesCounter;
+    }
+    [functionNamesCounter addObject:@(functionName)];
+  }
+  return self;
+}
+
+- (void)dealloc {
+  Class threadKey = [GTMSyncMonitorInternal class];
+
+  NSMutableDictionary *threadDict = [NSThread currentThread].threadDictionary;
+  NSMutableDictionary *counters = threadDict[threadKey];
+  NSCountedSet *functionNamesCounter = counters[_objectKey];
+  NSString *functionNameStr = @(_functionName);
+  NSUInteger numberOfSyncsByThisFunction = [functionNamesCounter countForObject:functionNameStr];
+  NSArray *stack = [NSThread callStackSymbols];
+  _GTMDevAssert(numberOfSyncsByThisFunction > 0, @"Sync not found on %@ at %s\n%@",
+                [_objectKey.nonretainedObjectValue class], _functionName,
+                [stack subarrayWithRange:NSMakeRange(1, stack.count - 1)]);
+  [functionNamesCounter removeObject:functionNameStr];
+  if (functionNamesCounter.count == 0) {
+    [counters removeObjectForKey:_objectKey];
+  }
+}
+
++ (NSArray *)functionsHoldingSynchronizationOnObject:(id)object {
+  Class threadKey = [GTMSyncMonitorInternal class];
+  NSValue *localObjectKey = [NSValue valueWithNonretainedObject:object];
+
+  NSMutableDictionary *threadDict = [NSThread currentThread].threadDictionary;
+  NSMutableDictionary *counters = threadDict[threadKey];
+  NSCountedSet *functionNamesCounter = counters[localObjectKey];
+  return functionNamesCounter.count > 0 ? functionNamesCounter.allObjects : nil;
+}
+
+@end
+
+#endif  // DEBUG