This seems, to me, a slightly more specific question that those already asked, so: How reliable is the Windows Event Log service if I'm looking for a 'fire and forget' logging service, so that even an error in calling the service does not impact the caller, and is noted somewhere, somehow, by the OS?
On Windows side, the event log is fine. Being used for so long by so many applications, it is definitely stable. I'm sure you can find creative ways to crash the API by feeding it bad enough input, but that's probably true with every API. When used properly it will work.
Having that said, you usually don't use the event log in a "fire and forget" context. Keep in mind it is a system-global log, which is supposed to be read by an administrator. Being fed too many events, it will become quite useless from the administrator's point of view. If you do use it sparsely and only for significant events, you can take your time and make sure your input is valid and no exceptions propagate back to your main logic.
Lastly, if you're looking for a real "fire and forget" logging infrastructure, take a look at ETW, which is a high performance event tracing infrastructure that is built into Windows.
In my experience, I have never had a programmatic issue with the Event Service. I did have an issue once, but it was a 4201(?) 'Access Denied' error caused by the Platforms "gurus" at my shop. But never anything regarding any usage or API calls.
The Windows event log has worked well for us in practice. The only problems that we had regarding stability were in the days of NT4 and are long gone in practice. Just make sure that you don't flood it with the same event repeatedly or it becomes a pain to actually look at ;)
Related
I have an app which needs almost no user interaction, but requires Geofences. Can I run this entirely within a background service?
There will be an Activity when the service is first run. This Activity will start a service and register a BroadcastReceiver for BOOT_COMPLETED, so the service will start at boot. It's unlikely that this Activity will ever be run again.
The service will set an Alarm to go off periodically, which will cause an IntentService to download a list of locations from the network. This IntentService will then set up Geofences around those locations, and create PendingIntents which will fire when the locations are approached. In turn, those PendingIntents will cause another IntentService to take some action.
All this needs to happen in the background, with no user interaction apart from starting the Activity for the first time after installation. Hence, the Activity will not interact with LocationClient or any location services.
I've actually got this set up with proximityAlerts, but wish to move to the new Geofencing API for battery life reasons. However, I have heard that there can be a few problems with using LocationClient from within a service. Specifically, what I've heard (sorry, no references, just hearsay claims):
location client relies on ui availability for error handling
when called from background thread, LocationClient.connect() assumes that it is called from main ui thread (or other thread with event looper), so connection callback is never called, if we call this method from service running in background thread
When I've investigated, I can't see any reason why this would be the case, or why it would stop my doing what I want. I was hoping it would be almost a drop-in replacement for proximityAlerts...
Can anyone shed some light on things here?
The best thing would be to just try it out, right? Your strategy seems sound.
when called from background thread, LocationClient.connect() assumes that it is called from main ui thread (or other thread with event looper), so connection callback is never called, if we call this method from service running in background thread.
I know this to be not true. I have a Service that is started from an Activity, and the connection callback is called.
I dont know about proximity alerts; but I cant seem to find an API to list my GeoFences. I am worried that my database (sqlite) and the actual fences might get out of sync. That is a design flaw in my opinion.
The reason LocationClient needs UI, is that the device may not have Google Play Services installed. Google has deviced a cunning and complex mechanism that allows your app to prompt the user to download it. The whole thing is horrible and awful in my opinion. Its all "what-if what-if" programming.
(They rushed a lot of stuff out the door for google IO 2013. Not all of it are well documented, and some of it seems a bit "rough around the edges").
We have a system where there are typically two processes running on the same system. One process handles the GUI and the other runs like a service (although for historical reasons, it's not a service, just an exe with no visible window).
The two processes undertake IPC mainly via registered messages asynchronously - i.e. we use RegisterWindowMessage() in both processes to define a large'ish set of messages that effectively form the API to the server process.
I have written a "hands-free" monitoring application that uses SetWindowsHookEx() to monitor and display the message queues of both processes and provide some level of decoding of the way the API is being utilised and how notifications are being propagated to the GUI process (each individual window can subscribe to notifications from the server directly).
So, there are a large number of messages in both directions so I have filtering and summary counts etc. so I can focus on particular activity. All this can be done without affecting the live code, which is good.
This all works well, but it now would be very useful to be able to "tag" a message originating in the GUI so I can trace the same message when it's processed by the server. This would be enormously useful for debugging and diagnosing system issues, but I can't find a clean way (actually I can't find any way!) of doing this without adding such support to our registered message API, which would be a lot of work and involves more risk than I'm comfortable with at the moment. It gets further complicated by the fact that the server pre-processes some messages and then does a PostMessage() back to itself to perform the action, so the originating message can get "lost".
Has anyone here tackled this type of problem? If so, can you give me some pointers? If not, then are there any documented or undocumented ways of adding a small block of data to a Windows message and retrieving it later? I've looked at SetMessageExtraInfo() but that seems to be per-queue rather than per-message.
FindWindow or FindWindowEx will give you the details of the GUI Window. Compare the details with message intercepted
I need to track to a log when a service or application in Windows is started, stopped, and whether it exits successfully or with an error code.
I understand that many services do not log their own start and stop times, or if they exit correctly, so it seems the way to go would have to be inserting a hook into the API that will catch when services/applications request a process space and relinquish it.
My question is what function do I need to hook in order to accomplish this, and is it even possible? I need it to work on Windows XP and 7, both 64-bit.
I think your best bet is to use a device driver. See PsSetCreateProcessNotifyRoutine.
Windows Vista has NotifyServiceStatusChange(), but only for single services. On earlier versions, it's not possible other than polling for changes or watching the event log.
If you're looking for a user-space solution, EnumProcesses() will return a current list. But it won't signal you with changes, you'd have to continually poll it and act on the differences.
If you're watching for a specific application or set of applications, consider assigning them to Job Objects, which are all about allowing you to place limits on processes and manage them externally. I think you could even associate Explorer with a job object, then all tasks launched by the user would be associated with your job object automatically. Something to look into, perhaps.
I've got a service that acts as a watchdog for several apps/servers. There are no user sessions on this machine. I'd like the watchdog to be capable of beeping on the internal speaker should something go wrong (that'd be my queue to go fix whatever it's complaining about)
when I try the Beep() API on Windows nothing happens - I suspect the problem is that the services session isnt permitted to make noises?
can I make this work? any other ideas for how to make the service alert me?
-CG
Call CreateFile on \device\beep, then send down IOCTL_BEEP_SET (see http://www.koders.com/c/fidFEC3527B9D951559D62722A9C0C603863106CA9B.aspx for details)
It may work if you allow it to interact with the desktop (an option configurable somewhere, I can't remember where).
But personally, I'd have it email me.
Though maybe you could have it use the task scheduling API to schedule a task for yourself, so next time you log on you can see it.
I don't know; you've got a few options. I'd avoid beeping though.
Try sending beep char "\a" to console. Not sure if it will work.
Beeping doesn't seem like a good idea - it might end up driving everyone mad....
I'd also agree about the "interact with desktop" option and you set this in the services parameters see A Windows Service without a template
I'd recommend creating a simple client application that polls that server to query for any problems and returns a set of status messages. Then an appropriate UI would be raised (e.g. balloon on the tray), an email sent, etc. containing any warning or failure messages.
This way you also know that the watchdog itself is running and has network connectivity - if the watchdog dies and/or machine locks up you wouldn't otherwise know.
It also avoids being thrown out of a window when the machine starts beeping continuously just after you go to lunch. [+1 to #mikej] :-)
The poll period should be around half (see Nyquist sampling rate) your minimum required response time.
Why not use the Windows scheduler?
I have several applications that have to run at certain times according to business rules not the typical every weekday at 1pm.
I also need a way for the applications to provide feedback of their progress so that I can have rules that notify me when the applications are running slow or aren't even running anymore.
What Windows API should I be looking into? (like, a time version of the FileWatcher apis)
What's the best way to have the application notify the scheduler of its progress (files, sockets, windows messages, ???)?
For Vista/Win2k8, there's the nice Task Scheduler 2.0 API: http://msdn.microsoft.com/en-us/library/aa384138(VS.85).aspx. Previous version have the Task Scheduler 1.0 API, but I've never used it.
AppControls has a CronJob component that you can use to create scheduled events. This saves your program from having to wake up every minute and check the schedule itself. Instead, just schedule the job and indicate a callback method.
I have used this component for scheduling jobs myself and have been very happy with the way that it works.
I think what you really want is a common framework for your applications that report to something (you or the system messages or tracing or perfmon, event log, whatever) and also to receive via some inter process protocol a way to receive messages and respond.
based on the reporting you can change the scheduling or make changes, etc.
So, there is some monitor app, and then each of your other apps does common reporting.
events I can think of:
- started
- stopped
- error
- normal log messages
- and of course specific things your apps do.
I think there are probably existing classes/framework that do this - you'll have to check around.
If it were me, I would make a service that could talk to all the other apps and perhaps was even an http server. It would be able to route messages to particular apps and start stop those processes and query them.
There are lots of ways to do what you want though. those were just off the top of my head.
Alternatively you might just be able to get these to be services and they handle messages sent to them. Their normal processing does nothing until they are "woken up" with some task command.
You have more questions in one. Normally you should split them. But let's overlook this and try to answer.
To schedule certain events (including running an application): Use TJvScheduledEvents from JVCL. IMHO JVCL is the best Delphi open source library around with extensive number of components, developers & support. TJvScheduledEvents is quite neat, uses threads for event scheduling and also you have in JVCL a detailed editor for your events (it needs a small hack to use it though).
To provide 'feedback' from your applications to a (remote) central point: A very very very good solution (if your requirements permit) is to log the progress of your applications in a table (let's call it LOG) on a Firebird server. In LOG you can have the following fields: COMPUTER, USERNAME, APPNAME, MSG, LOGDATE (etc. etc.). In the After Insert trigger of the LOG table you can fire an event (let's call it NEW_LOG). In your console app you can register the interest for this event and so, your application will be automatically updated with everything which happens in any of your applications, so you can do log analysis, graphs etc. Of course you can do it with IB, but IB costs.
...going on Windows API route you need headers (which probably aren't translated), you'll encounter our dearest Pointers/PChars etc. etc. Of course, building from scratch everything isn't worthwhile but when this is already done in a Delphi way, why don't use it?
Use service with a timer that is fired regulary (for example each minute). It reads the schedule and looks if some are due before the next iteration. If so, you can execute them.
You can add an interface that shows all running apps. For the feedback and query that using a desktop application.