I run the same code from two different locations in my application. I know it is the same code, because it is in a class and that class only has one publicly facing function. Both places call the function with the same arguments and both are running in the UI thread.
The function does a search for a particular printer by name using an asynchronous WMI query-->
var searcher =
new ManagementObjectSearcher(
"SELECT * from Win32_Printer WHERE Name LIKE '%ZDesigner GX430t'");
// Create an observer to trigger a callback when the search is completed.
var watcher = new ManagementOperationObserver();
watcher.Completed += PrinterSearchCompleted;
watcher.ObjectReady += PrinterSearchReady;
// Look for the printer
_printerFound = false;
_searchCompleted = false;
searcher.Get(watcher);
The problem I am having is that the ObjectReady event is not triggered when I run it from one location and when I run it from another, it get's triggered all the time.
Also, another problem is that this seems to be computer specific; some of the computers I run this on work just fine, others exhibit the problem I described above.
Any ideas what I should be looking for?
Couple of things to try:
Check if WMI service is running on all the computers.
Restart WMI service on the computers where it is not working.
You may find this article useful.
If its a Windows 7 or Windows Server 2008 R2 server, WMI has a memory leak problem. Check this.
Related
Can we use graph database neo4j with react js? If not so is there any alternate option for including graph database in react JS?
Easily, all you need is neo4j-driver: https://www.npmjs.com/package/neo4j-driver
Here is the most simplistic usage:
neo4j.js
//import { v1 as neo4j } from 'neo4j-driver'
const neo4j = require('neo4j-driver').v1
const driver = neo4j.driver('bolt://localhost', neo4j.auth.basic('username', 'password'))
const session = driver.session()
session
.run(`
MATCH (n:Node)
RETURN n AS someName
`)
.then((results) => {
results.records.forEach((record) => console.log(record.get('someName')))
session.close()
driver.close()
})
It is best practice to close the session always after you get the data. It is inexpensive and lightweight.
It is best practice to only close the driver session once your program is done (like Mongo DB). You will see extreme errors if you close the driver at a bad time, which is incredibly important to note if you are beginner. You will see errors like 'connection to server closed', etc. In async code, for example, if you run a query and close the driver before the results are parsed, you will have a bad time.
You can see in my example that I close the driver after, but only to illustrate proper cleanup. If you run this code in a standalone JS file to test, you will see node.js hangs after the query and you need to press CTRL + C to exit. Adding driver.close() fixes that. Normally, the driver is not closed until the program exits/crashes, which is never in a Backend API, and not until the user logs out in the Frontend.
Knowing this now, you are off to a great start.
Remember, session.close() immediately every time, and be careful with the driver.close().
You could put this code in a React component or action creator easily and render the data.
You will find it no different than hooking up and working with Axios.
You can run statements in a transaction also, which is beneficial for writelocking affected nodes. You should research that thoroughly first, but transaction flow is like this:
const session = driver.session()
const tx = session.beginTransaction()
tx
.run(query)
.then(// same as normal)
.catch(// errors)
// the difference is you can chain multiple transactions:
const tx1 = await tx.run().then()
// use results
const tx2 = await tx.run().then()
// then, once you are ready to commit the changes:
if (results.good !== true) {
tx.rollback()
session.close()
throw error
}
await tx.commit()
session.close()
const finalResults = { tx1, tx2 }
return finalResults
// in my experience, you have to await tx.commit
// in async/await syntax conditions, otherwise it may not commit properly
// that operation is not instant
tl;dr;
Yes, you can!
You are mixing two different technologies together. Neo4j is graph database and React.js is framework for front-end.
You can connect to Neo4j from JavaScript - http://neo4j.com/developer/javascript/
Interesting topic. I am using the driver in a React App and recently experienced some issues. I am closing the session every time a lifecycle hook completes like in your example. When there where more intensive queries I would see a timeout error. Going back to my setup decided to experiment by closing the driver in some more expensive queries and it looks like (still need more testing) the crashes are gone.
If you are deploying a real-world application I would urge you to think about Authentication and Authorization when using a DB-React setup only as you would have to store username/password of the neo4j server in the client. I am looking into options of having the Neo4J server issuing a token and receiving it for Authorization but the best practice is for sure to have a Node.js server in the middle with something like Passport to handle Authentication.
So, all in all, maybe the best scenario is to only use the driver in Node and have the browser always communicating with the Node server using axios...
I've implemented quartz.net in windows service to run tasks. And everything works fine on local workstation. But once it's deployed to remote win server host, it just hangs after initialization.
ISchedulerFactory schedFact = new StdSchedulerFactory();
// get a scheduler
var _scheduler = schedFact.GetScheduler();
// Configuration of triggers and jobs
var trigger = (ICronTrigger)TriggerBuilder.Create()
.WithIdentity("trigger1", "group1")
.WithCronSchedule(job.Value)
.Build();
var jobDetail = JobBuilder.Create(Type.GetType(job.Key)).StoreDurably(true)
.WithIdentity("job1", "group1").Build();
var ft = _scheduler.ScheduleJob(jobDetail, trigger);
Everything seems to be standard. I have private static pointer to scheduler, logging process stops right after jobs are initialized and added to scheduler. Nothing else happens after.
I'd appreciate any advices.
Thanks.
PS:
Found some strange events in event viewer mb according quartz.net:
Restart Manager - Starting session 2 - 2012-07-09T15:14:15.729569700Z.
Restart Manager - Ending session 2 started 2012-07-09T15:14:15.729569700Z.
Based on your question and the additional info you gave in comments, I would guess there is something going wrong in the onStart method of your service.
Here are some things you can do to help figure out and solve the problem:
Place the code in your onStart method in a try/catch block, and try to install and start the service. Then check windows logs to see if it was installed correctly, started correctly, etc.
The fact that restart manager is running leads me to believe that your service may be dependent on a process which is already in use. Make sure that any dependencies of your service are closed before installing it.
This problem can also be caused by putting data-intense or long running operations in your onStart method. Make sure that you keep this kind of code out of onStart.
I had a similar problem to this and it was caused by having dots/periods in the assembly name e.g. Project.Update.Service. When I changed it to ProjectUpdateService it worked fine.
Strangely it always worked on the development machine. Just never on the remote machine.
UPDATE: It may have been the length of the service that has caused this issue. By removing the dots I shortened the service name. It looks like the maximum length is 25 characters.
I have this line of code in my Delphi app:
sh := CoShellWindows.Create;
When run through a Citrix session, this raises an exception "Not enough storage is available to complete this operation."
Can someone confirm my suspicion that I can't access this through Citrix? I'm running in Seamless mode if that makes any difference. Maybe there's something I need to change on the published icon to make it work?
I am guessing that there is no "Shell" in Citrix to create.
Thanks
EDIT
The CoShellWindows is simply a class which creates an object which implements the IShellWindows interface. This interface is then used to iterate through it's items looking for an instance of Internet Explorer (or more specifically, an item which implements the IWebBrowser2 interface).
There are a few other use case scenarios using the CoShellWindows, but all ultimately are used to interact with the IWebBrowser2 interface (Internet Explorer 8). My requirement is to obtain this IWebBrowser2 object.
The call, behind the scenes is calling the Windows API CoCreateInstance with the following parameters:
rclsid = {9BA05972-F6A8-11CF-A442-00A0C90A8F39} (CLSID of
IShellWindows)
pUnkOuter = null (nil)
dwClsContext = CLSCTX_ALL (I've tried various combinations of these
flags)
riid = {85CB6900-4D95-11CF-960C-0080C7F4EE85} (IID of IShellWindows)
ppv = a variable declared as type IShellWindows
eg:CoCreateInstance(CLASS_ShellWindows, nil, CLSCTX_ALL, IID_IShellWindows, sh)
Your exception "Not enough storage is available to complete this operation." should really read "Shell does not exist so no instance can be created"
Basically you are correct in your assumption that there is no shell to create in Citrix.
What are you using the shell for? as if you provide more information we may well be able to offer a full work around.
I have got a dll that I load in my program which reads and writes its settings to the registry (hkcu). My program changes these settings prior to loading the dll so it uses the settings my program wants it to use which works fine.
Unfortunately I need to run several instances of my program with different settings for the dll. Now the approach I have used so far no longer works reliably because it is possible for one instance of the program to overwrite the settings that another instance just wrote before the dll has a chance to read them.
I haven't got the source of the dll in question and I cannot ask the programmer who wrote it to change it.
One idea I had, was to hook registry access functions and redirect them to a different branch of the registry which is specific to the instance of my program (e.g. use the process id as part of the path). I think this should work but maybe you have got a different / more elegant.
In case it matters: I am using Delphi 2007 for my program, the dll is probably written in C or C++.
As an alternative to API hooking, perhaps you could use RegOverridePredefKey API.
Instead of hooking the registry access for the dll, you can use an inter-process lock mechanism for writing the values to the registry for your own app. The idea being that the lock acquired by instance1 isn't released until its dll "instance" has read the values, so that when instance2 starts it won't acquire the lock until instance1 has finished. You'd need a locking mechanism that works between processes for this to work. For example mutexes.
To create mutexes:
procedure CreateMutexes(const MutexName: string);
//Creates the two mutexes checked for by the installer/uninstaller to see if
//the program is still running.
//One of the mutexes is created in the global name space (which makes it
//possible to access the mutex across user sessions in Windows XP); the other
//is created in the session name space (because versions of Windows NT prior
//to 4.0 TSE don't have a global name space and don't support the 'Global\'
//prefix).
const
SECURITY_DESCRIPTOR_REVISION = 1; // Win32 constant not defined in Delphi 3
var
SecurityDesc: TSecurityDescriptor;
SecurityAttr: TSecurityAttributes;
begin
// By default on Windows NT, created mutexes are accessible only by the user
// running the process. We need our mutexes to be accessible to all users, so
// that the mutex detection can work across user sessions in Windows XP. To
// do this we use a security descriptor with a null DACL.
InitializeSecurityDescriptor(#SecurityDesc, SECURITY_DESCRIPTOR_REVISION);
SetSecurityDescriptorDacl(#SecurityDesc, True, nil, False);
SecurityAttr.nLength := SizeOf(SecurityAttr);
SecurityAttr.lpSecurityDescriptor := #SecurityDesc;
SecurityAttr.bInheritHandle := False;
CreateMutex(#SecurityAttr, False, PChar(MutexName));
CreateMutex(#SecurityAttr, False, PChar('Global\' + MutexName));
end;
To release a mutex, you'd use the ReleaseMutex API and to acquire a created mutex, you'd use the OpenMutex API.
For CreateMutex see: http://msdn.microsoft.com/en-us/library/ms682411(VS.85).aspx
For OpenMutex see: http://msdn.microsoft.com/en-us/library/ms684315(v=VS.85).aspx
For ReleaseMutex see: http://msdn.microsoft.com/en-us/library/ms685066(v=VS.85).aspx
dirty method: open the dll in a hexeditor and change/alter the registry-path from the original hive to any other you want to use or have your proper settings.
I have a Windows Service that I inherited from a departed developer. The Windows Service is running just fine in the QA environment. When I install the service and run it locally, I receive this error:
Service cannot be started. System.InvalidOperationException: The requested Performance Counter is not a custom counter, it has to be initialized as ReadOnly.
Here is the code:
ExternalDataExchangeService exchangeService = new ExternalDataExchangeService();
workflowRuntime.AddService(exchangeService);
workflowRuntime.AddService(new SqlTrackingService(AppContext.SqlConnectionImportLog));
ChallengerWorkflowService challengerWorkflowService = new ChallengerWorkflowService();
challengerWorkflowService.SendDataEvent += new EventHandler<SendDataEventArgs>(challengerWorkflowService_SendDataEvent);
workflowRuntime.AddService(challengerWorkflowService);
workflowRuntime.StartRuntime(); <---- Exception is thrown here.
Check for installer code. Often you will find counters are created within an installation (which is going to of been run under admin privledges on client site) and the code then uses them as though they exist - but will not try create them because they do not expect to have the permissions.
If you just get the source and then try run it, the counters / counter classes do not exist so you fall over immediately. (Alternatively check whether the counter exists / you have local admin if they wrote the code to create it in the service.)
Seen it before so mentioned it.
Attach Debugger and break on InvalidOperationException (first-chance, i.e. when thrown)?