I'm writing an OS X launch agent (which watches, as it happens, for FSEvents);
it therefore has no UI and is not started from a bundle – it's just a program.
The relevant documentation and sample
code
illustrates persisting FS event IDs between invocations, and does so using
NSUserDefaults. This is clear the Right Thing To Do(TM).
The documentation for NSUserDefaults in the
Preferences and Settings Programming Guide
would appear to be the appropriate thing to read.
This shows only the Application and Global domains as being persistent, but (fairly
obviously) only the Application domain is writable for an application. However
the preferences in the application domain are keyed on the
ApplicationBundleIdentifier, which a launch agent won't have. So I'm at a loss
how such an agent should persist state.
All I can think of is that the Label in the launchd job can act as the
ApplicationBundleIdentifier – it at least has the correct form. But I can't see any
hint that that's correct, in the documentation.
The obvious (unix-normal) thing to do would be to write to a dot-file
in $HOME, but that's presumably not the Cocoa Way. Google searches
on 'osx daemon preferences', and the like, don't show up anything useful,
or else my google-fu is sadly lacking today. Googling for 'set application
bundle identifier' doesn't turn up anything likely, either.
NSUserDefaults:persistentDomainForName looks like it should be relevant,
but I can't work out its intentions from its method documentation.
I've found one question here which seems relevant, but while it's tantalisingly close, it doesn't say where the daemon gets its identifier from.
I've limited experience with Objective-C and Cocoa, which means that by
now I rather suspect I'm barking up the wrong tree, but don't really know where
to look next.
You can (and imo should) have an Info.plist even in a single-file executable.(see http://www.red-sweater.com/blog/2083/the-power-of-plist)
However, NSUserDefaults is a little more questionable. Conceptually, it's intended for user settings, rather than internal state. However, there's no real reason it wouldn't be suited to this, so I'd probably go ahead and do so.
Related
As soon as you hit "Play" what happens in the background of the software? The code is already compiled and ready at this point. So when I press "Play" the code gets executed. What other things occur along with this?
I have this question as an assignment and would really like to know. Thanks. :)
Actually everything is loaded by script. This graph explains the process. Also the links below can be useful for you to understand all the background process.
Execution Order of Event Functions
Overview: Script compilation
Asking what happens when you press Play is like asking Coke to reveal the drink recipe. This is what they sell. You got that as assignment, fact is you can say anything and your teacher would lie to tell you wrong, since he does not know either (except if he works for a company that bought the source code of the engine).
What you can say, is that the OpenGl/DirectX API is initialised, registration of all event to the OS like Input, application data and so on, then all the Engine functioning, registering of the needed classes in memory, init of the physics, parsing of the opening scene YAML file, creation of the content and placement in space, for each item, if a MonoBehaviour, registration of all callbacks, all the debug code related to profiler and stack tracing, crash reports and many more...
Those are the obvious ones and I cannot have any clue of what is going on without using a tool to decompose the code. Problem, it is against the EULA and then illegal.
I'm having a strange issue with my application for Mac OS X. I have a process that runs in a secondary thread. The process repeats a certain action a user-specified number of times in a for loop.
With each iteration of the for loop, there is a string that is initialized with the contents of a strings file. If the content of the strings file equals "YES" then the loop breaks (the file is set to "NO" by default). When the user wants to stop the loop, they hit the "Stop" button which sets the contents of the file to "YES".
This actually works great when I run the application in Xcode and when I export the application as a .app. The problem occurs when I actually turn the application into a pkg and install it. The stop function no longer operates correctly. I'm pretty stumped as to what the issue is. I'm initializing all my references to my file using [NSBundle mainBundle] so I should be referencing the file in my application bundle.
EDIT: I actually decided to switch to checking an atomic BOOL value within the loop that I change when the stop button is pressed. This seems to be a simpler solution for me.
Regular users do not have permission to modify applications installed in the /Application folder for very good security reasons. Also, signed apps (ie, any app sold through the App Store) cannot be modified without invalidating your signed code.
Never, ever, ever rely on the application bundle being modifiable. It's never supposed to be. Always use standard user data folders like "~/Library/Application Support/" or "~/Library/Caches/" for app-related, non-document files.
As to your general approach, repeatedly polling a file - especially in a tight loop - is a lot of disk activity. "Laptop Killah" would be a good name for the app. :-) You should consider changing this approach altogether. If you provide more detail in another question (what you're doing and why) and ask for suggestions, I'm almost positive there'll be a number of better ways that don't chew through your users' battery charge like crack-addled rats in a grocery store.
Also, I'm guessing you never check to see if your file is written successfully. The standard -writeToURL/File:... methods return a BOOL to signal success or failure as well as set an NSError (if you pass a pointer to one) with further details. Get into the habit of not ignoring this. In this case, you might've found your own answer because you'd have known just where your code is breaking. From there, it wouldn't have been a huge leap to figure out why.
Sometimes when looking at someone else's large Objective-C program, it is hard to know where to begin.
In such situations, I think it would be helpful to log every call to every non-Apple method.
Is there a way to do that? Basically, make one change in some central place, and log every method that is called. Preferably limited to non-Apple methods.
You can set the environment variable NSObjCMessageLoggingEnabled to YES. This will write a log of all message sends in the folder /tmp/msgSends-xxx.
You could add a symbolic breakpoint to objc_msgSend(), and have it log the second parameter without stopping.
How to do it for your own methods only though is a toucher task. Maybe if you could inspect the class name being called and do some magic to have a conditional breakpoint for only calls where the class' prefix matches your own?
I don't think logging every single call is practical enough to be useful, but here's a suggestion in that direction.
On a side note, if it's a large program, it better have some kind of documentation or an intro comment for people to get started with the code.
In any case, every Cocoa application has an applicationDidFinishLaunching... method. It's a good place to start from. Some apps also have their principal (or 'main window') class defined in the Info.plist file. Both these things might give you a hint as to what classes (specifically, view controllers) are the most prominent ones and what methods are likely to have long stack-traces while the program is running. Like a game-loop in a game engine, or some other frequently called method. By placing a breakpoint inside such a method and looking at the stack-trace in the debugger, you can get a general idea of what's going on.
If it's a UI-heavy app, looking at its NIB files and classes used in them may also help identify parts of app's functionality you might be looking for.
Another option is to fire up the Time Profiler instrument and check both Hide missing symbols and Hide system libraries checkboxes. This will give you not only a bird's eye view on the methods being called inside the program, but also will pin-point the most often called ones.
By interacting with your program with the Time Profiler recording on, you could also identify different parts of the program's functionality and correlate them with your actions pretty easily.
Instruments allows you to build your own "instruments", which are really just DTrace scripts in disguise. Use the menu option Instrument >> Build New Instrument and select options like which library you'd like to trace, what you'd like to record when you hit particular functions, etc. Go wild!
That's an interesting question. The answer would be more interesting if the solution supported multiple execution threads and there were some sort of call timeline that could report the activity over time (maybe especially with user events plotted in somehow).
I usually fire up the debugger, set a breakpoint at the main entry point (e.g. - applicationDidFinishLaunching:withOptions:) and walk it in the debugger.
On OSX, there are also some command-line tools (e.g. sample and heap) that can provide some insight.
It seems like some kind of integration with instruments could be really cool, but I am not aware of something that does exactly what you're wanting (and I want it now too after thinking about it).
If one were to log a thread number, and call address, and some frame details, it seems like the pieces would be there to plot the call timeline. The logic for figuring out the appropriate library (Apple-provided or third party) should exist in Apple's symbolicatecrash script.
Cloud App has this neat feature wherein it automatically uploads new screenshots as they are added to the Desktop. Any ideas how this is done?
You can do similar things yourself without much in the way of programming. In OSX, you can configure "Folder Actions" to run a script, for example, when a new item appears in a folder, including the Desktop. You can then use the script to do whatever you want with the new files.
This article at TUAW includes an example of uploading files to a web server when they hit a particular folder.
So, basically, the answer is "Folder Actions", or "something's keeping an eye on the folder and sending notifications", at some level. Whether Cloud App uses Folder Actions or watches the folder itself at a lower level, using FSEvents/NSWorkspace, or the kqueue mechanisms (for which there's a nice wrapper class called UKKQueue, if I remember correctly -- don't know how current my knowledge is on that one though!) is another matter...
You could implement this at several different levels, depending on the outcome you want, how you want to design whatever it is you're actually doing, and even what kind of filesystem you're targeting. Fundamentally, in Cocoa/Objective C, I think you probably want to start looking at FSEvents.
Once you've got notifications of the file changes, I'd probably use something like ConnectionKit to do the uploading -- any library at all, really, that means you don't have to bother with the sockets level yourself -- but again, there's a lot of different ways.
Depends, really, what level you're looking to solve the problem at, and whether you want to build something for other people or get something working for yourself. If I just wanted to bash something together for myself, I could probably have something cobbled together using Coda's Transmit app, and Folder Actions, or maybe Hazel, and a minimal bit of Applescript, in a half-hour at most, that would do the job well enough for me...
I am not sure what you are asking for exactly. If you are asking for a way to take a screenshot programmatically in MacOSX, I suggest you have a look at the "screencapture" command (in the terminal, type "man screencapture" for doc).
If you want to do it the "hard" way, you should look at this.
I have an old VW3/ENVY image with a parcel loaded as unmanaged code (exactly the situation Mastering ENVY/DEVELOPER warns against). Unfortunately, this problem happened a long time ago and it's too late to just "go back" to an image without the parcel loaded.
Apparently, there is a way to solve this problem (we have one development image where this has been solved, and there are normal configuration maps that contain the exact same code as the unmanaged parcel but they can't be loaded), but the exact way has long since been forgotten (and there are some problems with taking that particular dev image as the base for a new runtime image, so I need to find out how how to do it again).
In theory, it should be possible to remove the parcel and reload the code from a configuration map. In practice, all normal ways (using the ParcelBrowser or directly calling UnmanagedCode>>remove) fail. I even tried manually removing the offending selectors from the method dictionary, but past a certain point (involving a call to #primBecome:) the whole image hangs completely (I can't even drop into the debugger). I started hacking the instances of the classes and methods, hoping I'd trick ENVY into thinking that these particular methods are normal versioned code, but without any success yet.
Are there any smalltalk/envy gurus around that still remember enough of VW 3 to provide me with any pointers?
Status update
After a week of trying to solve the problem I finally made it, at least partially, so in case anyone's interested...
First, I had to fix file pointers for the umnanaged code (otherwise, all everything that tried to touch the methods would throw an exception). It looks like ENVY extends Parcel so that, in theory, all integer file pointers are changed to ENVY's void filepointer when loaded, but in my case, I had to do it manually (a Parcel provides enumeration for all selectors it defines). Another way would be to tweak the filePointer code, but that can't easily be done automatically on every image where it's needed.
Then, the parcel can be discarded, which drops the parcel information, but keeps the code. The official "Discard" mechanism needs to have a valid changes file (which envy doesn't use so it has to be set manually, and reset afterwards) and the parcel source (which we fortunately had).
To be able to make any changes to the methods (either manually, or via loading an application or class from ENVY), they need to get rid of their unmanaged status. This can be done by manually tweaking TheClass>>applicationAssocs (I also got rid of all references to the classes in UnmanagedCode sich as timestamps, and removed the reference to the discarded parcel). I actually had some info on how to get to this point from my boss, but I haven't been able to understand the instructions until I almost figured it out by myself.
This finally allowed me to load and reload all the Applications that contained the classes. In theory. In practice, the image still hung completely whenever I tried to load a newer version of the Application (that contained the code formerly in the parcel).
It turned out that the crashes had absolutely nothing to do with the code being unmanaged, but with the fact that the parcel in question modified InputState>>process:, where it caused an exception due to a missing and/or uninitialized class variable (the InputState>>initialize method wasn't called until after the new process: method was in place). I had to modify the Notifier class to dump all exceptions to a file to find out what was going on. Adding the class variable to the source of the class (instead of adding it via reflection), suspending the input processing thread via toBeLoadedCode and starting it again in the loaded method and creating a new version of the application solved even this problem.
Now everything works, in theory. In practice it's still unusable, because reloading the WindowSystem or VisualworksBase applications causes their initialization blocks to run, and a whole lot of settings are reset to their defaults - fonts and font sizes, window colors, UI settings... And there doesn't seem to be any way to just save the settings to a file and load them later on, or just to see what all the settings are (either the official Settings menu doesn't show everything, or we have a heavily tweaked image... so much for reconstructing it from scratch). But that's a completely different question.
Well, normally the recommendation would be that you should be able to rebuild your development image from scratch by loading your code from the repository. But if you had that, then the answer would be simple, just discard that image and reload. I think it's been long enough that I've lost whatever knowledge I've had about how to mess with the internal structures to get it back, and it sounds like you've tried a lot of things. So, although it might be painful, figuring out the recipe to rebuild your development image by loading stuff from the repository sounds like it may be your best bet. It probably isn't all that horrible, there just might be a few dependencies on the image state, or special doits that need to be executed.
You also probably need to validate what's in the repository against what's in the image you're working from. If there was unmanaged code loaded and then someone modified it and saved it, it's not clear to me that it would have been saved to ENVY. So you probably want to audit everything that was unmanaged code and if it's been changed, save that to a repository edition.
Sorry I don't have any better answers.