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#import "DDLog.h"
#import <pthread.h>
#import <objc/runtime.h>
#import <mach/mach_host.h>
#import <mach/host_info.h>
#import <libkern/OSAtomic.h>
/**
* Welcome to Cocoa Lumberjack!
*
* The project page has a wealth of documentation if you have any questions.
* https://github.com/robbiehanson/CocoaLumberjack
*
* If you're new to the project you may wish to read the "Getting Started" wiki.
* https://github.com/robbiehanson/CocoaLumberjack/wiki/GettingStarted
*
**/
#if ! __has_feature(objc_arc)
#warning This file must be compiled with ARC. Use -fobjc-arc flag (or convert project to ARC).
#endif
// Does ARC support support GCD objects?
// It does if the minimum deployment target is iOS 6+ or Mac OS X 10.8+
#if TARGET_OS_IPHONE
// Compiling for iOS
#if __IPHONE_OS_VERSION_MIN_REQUIRED >= 60000 // iOS 6.0 or later
#define NEEDS_DISPATCH_RETAIN_RELEASE 0
#else // iOS 5.X or earlier
#define NEEDS_DISPATCH_RETAIN_RELEASE 1
#endif
#else
// Compiling for Mac OS X
#if MAC_OS_X_VERSION_MIN_REQUIRED >= 1080 // Mac OS X 10.8 or later
#define NEEDS_DISPATCH_RETAIN_RELEASE 0
#else
#define NEEDS_DISPATCH_RETAIN_RELEASE 1 // Mac OS X 10.7 or earlier
#endif
#endif
// We probably shouldn't be using DDLog() statements within the DDLog implementation.
// But we still want to leave our log statements for any future debugging,
// and to allow other developers to trace the implementation (which is a great learning tool).
//
// So we use a primitive logging macro around NSLog.
// We maintain the NS prefix on the macros to be explicit about the fact that we're using NSLog.
#define DD_DEBUG NO
#define NSLogDebug(frmt, ...) do{ if(DD_DEBUG) NSLog((frmt), ##__VA_ARGS__); } while(0)
// Specifies the maximum queue size of the logging thread.
//
// Since most logging is asynchronous, its possible for rogue threads to flood the logging queue.
// That is, to issue an abundance of log statements faster than the logging thread can keepup.
// Typically such a scenario occurs when log statements are added haphazardly within large loops,
// but may also be possible if relatively slow loggers are being used.
//
// This property caps the queue size at a given number of outstanding log statements.
// If a thread attempts to issue a log statement when the queue is already maxed out,
// the issuing thread will block until the queue size drops below the max again.
#define LOG_MAX_QUEUE_SIZE 1000 // Should not exceed INT32_MAX
@interface DDLoggerNode : NSObject {
@public
id <DDLogger> logger;
dispatch_queue_t loggerQueue;
}
+ (DDLoggerNode *)nodeWithLogger:(id <DDLogger>)logger loggerQueue:(dispatch_queue_t)loggerQueue;
@end
@interface DDLog (PrivateAPI)
+ (void)lt_addLogger:(id <DDLogger>)logger;
+ (void)lt_removeLogger:(id <DDLogger>)logger;
+ (void)lt_removeAllLoggers;
+ (void)lt_log:(DDLogMessage *)logMessage;
+ (void)lt_flush;
@end
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
#pragma mark -
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
@implementation DDLog
// An array used to manage all the individual loggers.
// The array is only modified on the loggingQueue/loggingThread.
static NSMutableArray *loggers;
// All logging statements are added to the same queue to ensure FIFO operation.
static dispatch_queue_t loggingQueue;
// Individual loggers are executed concurrently per log statement.
// Each logger has it's own associated queue, and a dispatch group is used for synchrnoization.
static dispatch_group_t loggingGroup;
// In order to prevent to queue from growing infinitely large,
// a maximum size is enforced (LOG_MAX_QUEUE_SIZE).
static dispatch_semaphore_t queueSemaphore;
// Minor optimization for uniprocessor machines
static unsigned int numProcessors;
/**
* The runtime sends initialize to each class in a program exactly one time just before the class,
* or any class that inherits from it, is sent its first message from within the program. (Thus the
* method may never be invoked if the class is not used.) The runtime sends the initialize message to
* classes in a thread-safe manner. Superclasses receive this message before their subclasses.
*
* This method may also be called directly (assumably by accident), hence the safety mechanism.
**/
+ (void)initialize
{
static BOOL initialized = NO;
if (!initialized)
{
initialized = YES;
loggers = [[NSMutableArray alloc] initWithCapacity:4];
NSLogDebug(@"DDLog: Using grand central dispatch");
loggingQueue = dispatch_queue_create("cocoa.lumberjack", NULL);
loggingGroup = dispatch_group_create();
queueSemaphore = dispatch_semaphore_create(LOG_MAX_QUEUE_SIZE);
// Figure out how many processors are available.
// This may be used later for an optimization on uniprocessor machines.
host_basic_info_data_t hostInfo;
mach_msg_type_number_t infoCount;
infoCount = HOST_BASIC_INFO_COUNT;
host_info(mach_host_self(), HOST_BASIC_INFO, (host_info_t)&hostInfo, &infoCount);
unsigned int result = (unsigned int)(hostInfo.max_cpus);
unsigned int one = (unsigned int)(1);
numProcessors = MAX(result, one);
NSLogDebug(@"DDLog: numProcessors = %u", numProcessors);
#if TARGET_OS_IPHONE
NSString *notificationName = @"UIApplicationWillTerminateNotification";
#else
NSString *notificationName = @"NSApplicationWillTerminateNotification";
#endif
[[NSNotificationCenter defaultCenter] addObserver:self
selector:@selector(applicationWillTerminate:)
name:notificationName
object:nil];
}
}
/**
* Provides access to the logging queue.
**/
+ (dispatch_queue_t)loggingQueue
{
return loggingQueue;
}
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
#pragma mark Notifications
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+ (void)applicationWillTerminate:(NSNotification *)notification
{
[self flushLog];
}
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
#pragma mark Logger Management
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+ (void)addLogger:(id <DDLogger>)logger
{
if (logger == nil) return;
dispatch_async(loggingQueue, ^{ @autoreleasepool {
[self lt_addLogger:logger];
}});
}
+ (void)removeLogger:(id <DDLogger>)logger
{
if (logger == nil) return;
dispatch_async(loggingQueue, ^{ @autoreleasepool {
[self lt_removeLogger:logger];
}});
}
+ (void)removeAllLoggers
{
dispatch_async(loggingQueue, ^{ @autoreleasepool {
[self lt_removeAllLoggers];
}});
}
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
#pragma mark Master Logging
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+ (void)queueLogMessage:(DDLogMessage *)logMessage asynchronously:(BOOL)asyncFlag
{
// We have a tricky situation here...
//
// In the common case, when the queueSize is below the maximumQueueSize,
// we want to simply enqueue the logMessage. And we want to do this as fast as possible,
// which means we don't want to block and we don't want to use any locks.
//
// However, if the queueSize gets too big, we want to block.
// But we have very strict requirements as to when we block, and how long we block.
//
// The following example should help illustrate our requirements:
//
// Imagine that the maximum queue size is configured to be 5,
// and that there are already 5 log messages queued.
// Let us call these 5 queued log messages A, B, C, D, and E. (A is next to be executed)
//
// Now if our thread issues a log statement (let us call the log message F),
// it should block before the message is added to the queue.
// Furthermore, it should be unblocked immediately after A has been unqueued.
//
// The requirements are strict in this manner so that we block only as long as necessary,
// and so that blocked threads are unblocked in the order in which they were blocked.
//
// Returning to our previous example, let us assume that log messages A through E are still queued.
// Our aforementioned thread is blocked attempting to queue log message F.
// Now assume we have another separate thread that attempts to issue log message G.
// It should block until log messages A and B have been unqueued.
// We are using a counting semaphore provided by GCD.
// The semaphore is initialized with our LOG_MAX_QUEUE_SIZE value.
// Everytime we want to queue a log message we decrement this value.
// If the resulting value is less than zero,
// the semaphore function waits in FIFO order for a signal to occur before returning.
//
// A dispatch semaphore is an efficient implementation of a traditional counting semaphore.
// Dispatch semaphores call down to the kernel only when the calling thread needs to be blocked.
// If the calling semaphore does not need to block, no kernel call is made.
dispatch_semaphore_wait(queueSemaphore, DISPATCH_TIME_FOREVER);
// We've now sure we won't overflow the queue.
// It is time to queue our log message.
dispatch_block_t logBlock = ^{ @autoreleasepool {
[self lt_log:logMessage];
}};
if (asyncFlag)
dispatch_async(loggingQueue, logBlock);
else
dispatch_sync(loggingQueue, logBlock);
}
+ (void)log:(BOOL)asynchronous
level:(int)level
flag:(int)flag
context:(int)context
file:(const char *)file
function:(const char *)function
line:(int)line
tag:(id)tag
format:(NSString *)format, ...
{
va_list args;
if (format)
{
va_start(args, format);
NSString *logMsg = [[NSString alloc] initWithFormat:format arguments:args];
DDLogMessage *logMessage = [[DDLogMessage alloc] initWithLogMsg:logMsg
level:level
flag:flag
context:context
file:file
function:function
line:line
tag:tag
options:0];
[self queueLogMessage:logMessage asynchronously:asynchronous];
va_end(args);
}
}
+ (void)log:(BOOL)asynchronous
level:(int)level
flag:(int)flag
context:(int)context
file:(const char *)file
function:(const char *)function
line:(int)line
tag:(id)tag
format:(NSString *)format
args:(va_list)args
{
if (format)
{
NSString *logMsg = [[NSString alloc] initWithFormat:format arguments:args];
DDLogMessage *logMessage = [[DDLogMessage alloc] initWithLogMsg:logMsg
level:level
flag:flag
context:context
file:file
function:function
line:line
tag:tag
options:0];
[self queueLogMessage:logMessage asynchronously:asynchronous];
}
}
+ (void)flushLog
{
dispatch_sync(loggingQueue, ^{ @autoreleasepool {
[self lt_flush];
}});
}
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
#pragma mark Registered Dynamic Logging
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+ (BOOL)isRegisteredClass:(Class)class
{
SEL getterSel = @selector(ddLogLevel);
SEL setterSel = @selector(ddSetLogLevel:);
#if TARGET_OS_IPHONE && !TARGET_IPHONE_SIMULATOR
// Issue #6 (GoogleCode) - Crashes on iOS 4.2.1 and iPhone 4
//
// Crash caused by class_getClassMethod(2).
//
// "It's a bug with UIAccessibilitySafeCategory__NSObject so it didn't pop up until
// users had VoiceOver enabled [...]. I was able to work around it by searching the
// result of class_copyMethodList() instead of calling class_getClassMethod()"
BOOL result = NO;
unsigned int methodCount, i;
Method *methodList = class_copyMethodList(object_getClass(class), &methodCount);
if (methodList != NULL)
{
BOOL getterFound = NO;
BOOL setterFound = NO;
for (i = 0; i < methodCount; ++i)
{
SEL currentSel = method_getName(methodList[i]);
if (currentSel == getterSel)
{
getterFound = YES;
}
else if (currentSel == setterSel)
{
setterFound = YES;
}
if (getterFound && setterFound)
{
result = YES;
break;
}
}
free(methodList);
}
return result;
#else
// Issue #24 (GitHub) - Crashing in in ARC+Simulator
//
// The method +[DDLog isRegisteredClass] will crash a project when using it with ARC + Simulator.
// For running in the Simulator, it needs to execute the non-iOS code.
Method getter = class_getClassMethod(class, getterSel);
Method setter = class_getClassMethod(class, setterSel);
if ((getter != NULL) && (setter != NULL))
{
return YES;
}
return NO;
#endif
}
+ (NSArray *)registeredClasses
{
int numClasses, i;
// We're going to get the list of all registered classes.
// The Objective-C runtime library automatically registers all the classes defined in your source code.
//
// To do this we use the following method (documented in the Objective-C Runtime Reference):
//
// int objc_getClassList(Class *buffer, int bufferLen)
//
// We can pass (NULL, 0) to obtain the total number of
// registered class definitions without actually retrieving any class definitions.
// This allows us to allocate the minimum amount of memory needed for the application.
numClasses = objc_getClassList(NULL, 0);
// The numClasses method now tells us how many classes we have.
// So we can allocate our buffer, and get pointers to all the class definitions.
Class *classes = (Class *)malloc(sizeof(Class) * numClasses);
numClasses = objc_getClassList(classes, numClasses);
// We can now loop through the classes, and test each one to see if it is a DDLogging class.
NSMutableArray *result = [NSMutableArray arrayWithCapacity:numClasses];
for (i = 0; i < numClasses; i++)
{
Class class = classes[i];
if ([self isRegisteredClass:class])
{
[result addObject:class];
}
}
free(classes);
return result;
}
+ (NSArray *)registeredClassNames
{
NSArray *registeredClasses = [self registeredClasses];
NSMutableArray *result = [NSMutableArray arrayWithCapacity:[registeredClasses count]];
for (Class class in registeredClasses)
{
[result addObject:NSStringFromClass(class)];
}
return result;
}
+ (int)logLevelForClass:(Class)aClass
{
if ([self isRegisteredClass:aClass])
{
return [aClass ddLogLevel];
}
return -1;
}
+ (int)logLevelForClassWithName:(NSString *)aClassName
{
Class aClass = NSClassFromString(aClassName);
return [self logLevelForClass:aClass];
}
+ (void)setLogLevel:(int)logLevel forClass:(Class)aClass
{
if ([self isRegisteredClass:aClass])
{
[aClass ddSetLogLevel:logLevel];
}
}
+ (void)setLogLevel:(int)logLevel forClassWithName:(NSString *)aClassName
{
Class aClass = NSClassFromString(aClassName);
[self setLogLevel:logLevel forClass:aClass];
}
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
#pragma mark Logging Thread
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
/**
* This method should only be run on the logging thread/queue.
**/
+ (void)lt_addLogger:(id <DDLogger>)logger
{
// Add to loggers array.
// Need to create loggerQueue if loggerNode doesn't provide one.
dispatch_queue_t loggerQueue = NULL;
if ([logger respondsToSelector:@selector(loggerQueue)])
{
// Logger may be providing its own queue
loggerQueue = [logger loggerQueue];
}
if (loggerQueue == nil)
{
// Automatically create queue for the logger.
// Use the logger name as the queue name if possible.
const char *loggerQueueName = NULL;
if ([logger respondsToSelector:@selector(loggerName)])
{
loggerQueueName = [[logger loggerName] UTF8String];
}
loggerQueue = dispatch_queue_create(loggerQueueName, NULL);
}
DDLoggerNode *loggerNode = [DDLoggerNode nodeWithLogger:logger loggerQueue:loggerQueue];
[loggers addObject:loggerNode];
if ([logger respondsToSelector:@selector(didAddLogger)])
{
dispatch_async(loggerNode->loggerQueue, ^{ @autoreleasepool {
[logger didAddLogger];
}});
}
}
/**
* This method should only be run on the logging thread/queue.
**/
+ (void)lt_removeLogger:(id <DDLogger>)logger
{
// Find associated loggerNode in list of added loggers
DDLoggerNode *loggerNode = nil;
for (DDLoggerNode *node in loggers)
{
if (node->logger == logger)
{
loggerNode = node;
break;
}
}
if (loggerNode == nil)
{
NSLogDebug(@"DDLog: Request to remove logger which wasn't added");
return;
}
// Notify logger
if ([logger respondsToSelector:@selector(willRemoveLogger)])
{
dispatch_async(loggerNode->loggerQueue, ^{ @autoreleasepool {
[logger willRemoveLogger];
}});
}
// Remove from loggers array
[loggers removeObject:loggerNode];
}
/**
* This method should only be run on the logging thread/queue.
**/
+ (void)lt_removeAllLoggers
{
// Notify all loggers
for (DDLoggerNode *loggerNode in loggers)
{
if ([loggerNode->logger respondsToSelector:@selector(willRemoveLogger)])
{
dispatch_async(loggerNode->loggerQueue, ^{ @autoreleasepool {
[loggerNode->logger willRemoveLogger];
}});
}
}
// Remove all loggers from array
[loggers removeAllObjects];
}
/**
* This method should only be run on the logging thread/queue.
**/
+ (void)lt_log:(DDLogMessage *)logMessage
{
// Execute the given log message on each of our loggers.
if (numProcessors > 1)
{
// Execute each logger concurrently, each within its own queue.
// All blocks are added to same group.
// After each block has been queued, wait on group.
//
// The waiting ensures that a slow logger doesn't end up with a large queue of pending log messages.
// This would defeat the purpose of the efforts we made earlier to restrict the max queue size.
for (DDLoggerNode *loggerNode in loggers)
{
dispatch_group_async(loggingGroup, loggerNode->loggerQueue, ^{ @autoreleasepool {
[loggerNode->logger logMessage:logMessage];
}});
}
dispatch_group_wait(loggingGroup, DISPATCH_TIME_FOREVER);
}
else
{
// Execute each logger serialy, each within its own queue.
for (DDLoggerNode *loggerNode in loggers)
{
dispatch_sync(loggerNode->loggerQueue, ^{ @autoreleasepool {
[loggerNode->logger logMessage:logMessage];
}});
}
}
// If our queue got too big, there may be blocked threads waiting to add log messages to the queue.
// Since we've now dequeued an item from the log, we may need to unblock the next thread.
// We are using a counting semaphore provided by GCD.
// The semaphore is initialized with our LOG_MAX_QUEUE_SIZE value.
// When a log message is queued this value is decremented.
// When a log message is dequeued this value is incremented.
// If the value ever drops below zero,
// the queueing thread blocks and waits in FIFO order for us to signal it.
//
// A dispatch semaphore is an efficient implementation of a traditional counting semaphore.
// Dispatch semaphores call down to the kernel only when the calling thread needs to be blocked.
// If the calling semaphore does not need to block, no kernel call is made.
dispatch_semaphore_signal(queueSemaphore);
}
/**
* This method should only be run on the background logging thread.
**/
+ (void)lt_flush
{
// All log statements issued before the flush method was invoked have now been executed.
//
// Now we need to propogate the flush request to any loggers that implement the flush method.
// This is designed for loggers that buffer IO.
for (DDLoggerNode *loggerNode in loggers)
{
if ([loggerNode->logger respondsToSelector:@selector(flush)])
{
dispatch_group_async(loggingGroup, loggerNode->loggerQueue, ^{ @autoreleasepool {
[loggerNode->logger flush];
}});
}
}
dispatch_group_wait(loggingGroup, DISPATCH_TIME_FOREVER);
}
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
#pragma mark Utilities
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
NSString *DDExtractFileNameWithoutExtension(const char *filePath, BOOL copy)
{
if (filePath == NULL) return nil;
char *lastSlash = NULL;
char *lastDot = NULL;
char *p = (char *)filePath;
while (*p != '\0')
{
if (*p == '/')
lastSlash = p;
else if (*p == '.')
lastDot = p;
p++;
}
char *subStr;
NSUInteger subLen;
if (lastSlash)
{
if (lastDot)
{
// lastSlash -> lastDot
subStr = lastSlash + 1;
subLen = lastDot - subStr;
}
else
{
// lastSlash -> endOfString
subStr = lastSlash + 1;
subLen = p - subStr;
}
}
else
{
if (lastDot)
{
// startOfString -> lastDot
subStr = (char *)filePath;
subLen = lastDot - subStr;
}
else
{
// startOfString -> endOfString
subStr = (char *)filePath;
subLen = p - subStr;
}
}
if (copy)
{
return [[NSString alloc] initWithBytes:subStr
length:subLen
encoding:NSUTF8StringEncoding];
}
else
{
// We can take advantage of the fact that __FILE__ is a string literal.
// Specifically, we don't need to waste time copying the string.
// We can just tell NSString to point to a range within the string literal.
return [[NSString alloc] initWithBytesNoCopy:subStr
length:subLen
encoding:NSUTF8StringEncoding
freeWhenDone:NO];
}
}
@end
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
#pragma mark -
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
@implementation DDLoggerNode
- (id)initWithLogger:(id <DDLogger>)aLogger loggerQueue:(dispatch_queue_t)aLoggerQueue
{
if ((self = [super init]))
{
logger = aLogger;
if (aLoggerQueue) {
loggerQueue = aLoggerQueue;
#if NEEDS_DISPATCH_RETAIN_RELEASE
dispatch_retain(loggerQueue);
#endif
}
}
return self;
}
+ (DDLoggerNode *)nodeWithLogger:(id <DDLogger>)logger loggerQueue:(dispatch_queue_t)loggerQueue
{
return [[DDLoggerNode alloc] initWithLogger:logger loggerQueue:loggerQueue];
}
- (void)dealloc
{
#if NEEDS_DISPATCH_RETAIN_RELEASE
if (loggerQueue) dispatch_release(loggerQueue);
#endif
}
@end
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
#pragma mark -
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
@implementation DDLogMessage
static char *dd_str_copy(const char *str)
{
if (str == NULL) return NULL;
size_t length = strlen(str);
char * result = malloc(length + 1);
strncpy(result, str, length);
result[length] = 0;
return result;
}
- (id)initWithLogMsg:(NSString *)msg
level:(int)level
flag:(int)flag
context:(int)context
file:(const char *)aFile
function:(const char *)aFunction
line:(int)line
tag:(id)aTag
options:(DDLogMessageOptions)optionsMask
{
if ((self = [super init]))
{
logMsg = msg;
logLevel = level;
logFlag = flag;
logContext = context;
lineNumber = line;
tag = aTag;
options = optionsMask;
if (options & DDLogMessageCopyFile)
file = dd_str_copy(aFile);
else
file = (char *)aFile;
if (options & DDLogMessageCopyFunction)
file = dd_str_copy(aFunction);
else
function = (char *)aFunction;
timestamp = [[NSDate alloc] init];
machThreadID = pthread_mach_thread_np(pthread_self());
queueLabel = dd_str_copy(dispatch_queue_get_label(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0)));
threadName = [[NSThread currentThread] name];
}
return self;
}
- (NSString *)threadID
{
return [[NSString alloc] initWithFormat:@"%x", machThreadID];
}
- (NSString *)fileName
{
return DDExtractFileNameWithoutExtension(file, NO);
}
- (NSString *)methodName
{
if (function == NULL)
return nil;
else
return [[NSString alloc] initWithUTF8String:function];
}
- (void)dealloc
{
if (file && (options & DDLogMessageCopyFile))
free(file);
if (function && (options & DDLogMessageCopyFunction))
free(function);
if (queueLabel)
free(queueLabel);
}
@end
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
#pragma mark -
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
@implementation DDAbstractLogger
- (id)init
{
if ((self = [super init]))
{
const char *loggerQueueName = NULL;
if ([self respondsToSelector:@selector(loggerName)])
{
loggerQueueName = [[self loggerName] UTF8String];
}
loggerQueue = dispatch_queue_create(loggerQueueName, NULL);
}
return self;
}
- (void)dealloc
{
#if NEEDS_DISPATCH_RETAIN_RELEASE
if (loggerQueue) dispatch_release(loggerQueue);
#endif
}
- (void)logMessage:(DDLogMessage *)logMessage
{
// Override me
}
- (id <DDLogFormatter>)logFormatter
{
// This method must be thread safe and intuitive.
// Therefore if somebody executes the following code:
//
// [logger setLogFormatter:myFormatter];
// formatter = [logger logFormatter];
//
// They would expect formatter to equal myFormatter.
// This functionality must be ensured by the getter and setter method.
//
// The thread safety must not come at a cost to the performance of the logMessage method.
// This method is likely called sporadically, while the logMessage method is called repeatedly.
// This means, the implementation of this method:
// - Must NOT require the logMessage method to acquire a lock.
// - Must NOT require the logMessage method to access an atomic property (also a lock of sorts).
//
// Thread safety is ensured by executing access to the formatter variable on the loggerQueue.
// This is the same queue that the logMessage method operates on.
//
// Note: The last time I benchmarked the performance of direct access vs atomic property access,
// direct access was over twice as fast on the desktop and over 6 times as fast on the iPhone.
//
//
// loggerQueue : Our own private internal queue that the logMessage method runs on.
// Operations are added to this queue from the global loggingQueue.
//
// loggingQueue : The queue that all log messages go through before they arrive in our loggerQueue.
//
// It is important to note that, while the loggerQueue is used to create thread-safety for our formatter,
// changes to the formatter variable are queued through the loggingQueue.
//
// Since this will obviously confuse the hell out of me later, here is a better description.
// Imagine the following code:
//
// DDLogVerbose(@"log msg 1");
// DDLogVerbose(@"log msg 2");
// [logger setFormatter:myFormatter];
// DDLogVerbose(@"log msg 3");
//
// Our intuitive requirement means that the new formatter will only apply to the 3rd log message.
// But notice what happens if we have asynchronous logging enabled for verbose mode.
//
// Log msg 1 starts executing asynchronously on the loggingQueue.
// The loggingQueue executes the log statement on each logger concurrently.
// That means it executes log msg 1 on our loggerQueue.
// While log msg 1 is executing, log msg 2 gets added to the loggingQueue.
// Then the user requests that we change our formatter.
// So at this exact moment, our queues look like this:
//
// loggerQueue : executing log msg 1, nil
// loggingQueue : executing log msg 1, log msg 2, nil
//
// So direct access to the formatter is only available if requested from the loggerQueue.
// In all other circumstances we need to go through the loggingQueue to get the proper value.
dispatch_queue_t currentQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
if (currentQueue == loggerQueue)
{
return formatter;
}
else
{
dispatch_queue_t globalLoggingQueue = [DDLog loggingQueue];
NSAssert(currentQueue != globalLoggingQueue, @"Core architecture requirement failure");
__block id <DDLogFormatter> result;
dispatch_sync(globalLoggingQueue, ^{
dispatch_sync(loggerQueue, ^{
result = formatter;
});
});
return result;
}
}
- (void)setLogFormatter:(id <DDLogFormatter>)logFormatter
{
// The design of this method is documented extensively in the logFormatter message (above in code).
dispatch_block_t block = ^{ @autoreleasepool {
if (formatter != logFormatter)
{
if ([formatter respondsToSelector:@selector(willRemoveFromLogger:)]) {
[formatter willRemoveFromLogger:self];
}
formatter = logFormatter;
if ([formatter respondsToSelector:@selector(didAddToLogger:)]) {
[formatter didAddToLogger:self];
}
}
}};
dispatch_queue_t currentQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
if (currentQueue == loggerQueue)
{
block();
}
else
{
dispatch_queue_t globalLoggingQueue = [DDLog loggingQueue];
NSAssert(currentQueue != globalLoggingQueue, @"Core architecture requirement failure");
dispatch_async(globalLoggingQueue, ^{
dispatch_async(loggerQueue, block);
});
}
}
- (dispatch_queue_t)loggerQueue
{
return loggerQueue;
}
- (NSString *)loggerName
{
return NSStringFromClass([self class]);
}
@end
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