I'm new to this so sorry in case my question seems to be silly, I'm writing a Delphi program in which I'm running a list of external executables though multiple threads in a queue and waiting for them to finish using CreateProcess like:
CreateProcess(Pchar(NotepadExe), Nil, Nil, Nil,
False, NORMAL_PRIORITY_CLASS,
Nil, Nil, StartupInfo,ProcessInfo),
and
WaitForSingleObject(ProcessInfo.hProcess, INFINITE);
now the programs I called are performing lengthy jobs, so in case my program got closed while the external executables are still running, is there an easy way to regain access to the processes and waiting for them again? and what about the case when some of them are finished already?
I did sort of what #SertacAkyuz suggested, and it works
During execution I add the current process id to a file using
GetCurrentProcessId
When I start my program I read from the file the saved processIds then determine which of the currently running processes are children which I already ran, afterwards I create a thread to open and monitor the same again
uses tlhelp32;
----
var Snap:THandle;
ProcessE:TProcessEntry32;
----
Snap:=CreateToolhelp32Snapshot(TH32CS_SNAPALL, 0);
ProcessE.dwSize:=SizeOf(ProcessE);
if Process32First(Snap,ProcessE) then
begin \\Iterate through running processes
while Process32Next(Snap,ProcessE) do
\\Determine whether it's a child process of the saved PiD
if ProcessE.th32ParentProcessID = mySavedPiD then
\\ Creating the thread to monitor the process
cnThread:=TContinueThread.Create(ProcessE.th32ProcessID);
cnThread.Start;
\\ In the thread Execute
var hndl:THandle;
----
hndl:=OpenProcess(PROCESS_ALL_ACCESS ,False,PiD);
WaitForSingleObject(hndl, INFINITE);
It might not be the best solution but it works for me for now, however, still I need to handle the delta (processes which got finished during my program absence)
Creating a thread for each started process, wastes a thread. And the internal thread resources are limited. If you're using WaitForSingleObject(,INFINITE) now, take the time to learn about WaitForMultipleObjects and start a single thread to wait on a number of processes. (Or learn about jobs like #DavidHeffernan proposes)
Related
I create a mutex at the start of the my application, primarily to prevent running 2 instances of same application.
if CreateMutex(nil,false,'Proton Studio') = 0 then
RaiseLastOSError;
if GetLastError = ERROR_ALREADY_EXISTS then exit;
However, when I reconfigure my application I need to release the mutex before the application is closed in order to start a short program which will then restart my application.
hw := OpenMutex(MUTEX_ALL_ACCESS, false, 'Proton Studio');
if ReleaseMutex(hw)then begin
if ShellExecute(application.Handle, 'open',
Pchar('StudioRestart.exe'), PChar(Application.ExeName),'', SW_SHOWNORMAL) > 32 then
fmIDEMain.Close
else
ShowMessage('Unable to Restart, please close and restart manually')
end
OpenMutex returns a handle but when I call ReleaseMutex the function returns false. How should I close this mutex?
You seem to use the existence of the mutex as the criterion to decide whether the process already runs and not who owns the mutex. ReleaseMutex is used to give up ownership of a mutex if you currently own it. But your code doesn't actually retrieve ownership of the mutex anywhere.
I see these ways towards solving your problem:
Destroy mutex instead of trying to release it.
Instead of using ReleaseMutex, use CloseHandle to destroy the mutex. If you are the only one holding a handle to the mutex, it will be gone afterwards.
For this purpose, remember the original handle returned by CreateMutex and don't open the mutex a second time.
Use mutexes as intended
Instead of using the mere existing of the mutex, try to obtain ownership by calling WaitForSingleObject on it. You can then release it by calling ReleaseMutex.
External program should wait (my preferred method)
Have the external program wait until the old instance of the application was fully terminated before trying to start a new instance.
I am trying to understand why an installation file hangs up using Windbg, but I am at a point where I can't stop the execution.
As background, I had already been able to install this program on the same PC, but for some reason I had then uninstalled, and now I can't re-install it (I tried to clean up everything from the old installation, incl. registry). Now this setup.exe starts and stays idle among the running processes without doing anything.
But let's go to the actual question. I am trying to use Windbg for the first time (I only had some practice with the old 8086 debug at DOS-time :-), so please bear with me if I'm asking something straightforward).
I have tracked the code up to a point where I have a RET code. I am able to stop the debugger at the RET instruction, but as soon as I "step into" the RET, the execution starts and does not stop, while I was expecting it to just go to the instruction following the previous CALL. From how I see things, it seems that after the RET the execution goes somewhere else ... how is it possible? Also, just before the RET there is a SYSCALL that I don't fully understand ... can it have an impact?
This is the portion of the code I am examining at the moment:
ntdll!NtTerminateThread:
00007ff9`fc8b5b20 4c8bd1 mov r10,rcx
00007ff9`fc8b5b23 b853000000 mov eax,53h
00007ff9`fc8b5b28 f604250803fe7f01 test byte ptr [SharedUserData+0x308 (00000000`7ffe0308)],1
00007ff9`fc8b5b30 7503 jne ntdll!NtTerminateThread+0x15 (00007ff9`fc8b5b35)
00007ff9`fc8b5b32 0f05 syscall
00007ff9`fc8b5b34 c3 ret
00007ff9`fc8b5b35 cd2e int 2Eh
00007ff9`fc8b5b37 c3 ret
I am stuck at the first RET instruction, at address 5b34.
At this time, this is the stack call:
00000000`0203fc38 00007ff9`fc86c63e ntdll!NtTerminateThread+0x14
00000000`0203fc40 00007ff9`fc8d903a ntdll!RtlExitUserThread+0x4e
00000000`0203fc80 00007ff9`fc86c5c5 ntdll!DbgUiRemoteBreakin+0x5a
00000000`0203fcb0 00000000`00000000 ntdll!RtlUserThreadStart+0x45
so my understanding is that execution should continue at address 00007ff9`fc86c63e. However, even if I add a BP at this address, or if I just go for a trace, the execution continues and keeps running some idle loop until I hit the "pause" button in windbg, after which it resume at a completely different address.
In case the registers are relevant, here are some of them:
rax: 353000
rbx: 0
rcx: 0
rdx: 0
rsp: 203fc38
rdi: 7ff9c8d8fe0
rip: 7ff9fc8b5b34
So, eventually, where am I wrong? How can I see where the code goes after this RET?
Thanks in advance for any help,
Bob
when a thread exits the execution wont return to the return address
the system is free to schedule another thread that is ready in the process
the stack shows NtTerminateThread on the stack it is a function that does not return
__declspec noreturn foo (...) ;
btw when you say it goes elsewhere do you mean the app keeps running and is not terminated if so hit ctrl+break and check what other threads are doing
ie if usermode ~*kb should show all the threads callstack
answering the comment about where it goes
process is a collection of threads
each thread has a stack and each thread gets a bit of time to execute from the scheduler (thread quantum)
each thread that has a lower priority can be preempted by threads xxxx ,yyy ,zzz with higher priorities by interrupts by apcs , dpcs etc
when a thread has completed its quantum or is preempted by some vip cavalcade happening to travel on the road that this poor thread is walking
a trap is made _KTRAP and this poor threads position EIP is filled into it and put in a waiting threads barricade
when the vip cavalcade's dust has settled police open the barricade and let the poor thread walk from where it stopped
for such gory details you may need a kernel debugging setup and may need to control your process from a kernel debugger
when you hit the return os sees the thread is dead and has no return address
so it checks the !ready threads and selects the highest priority thread and provides it a quantum to enjoy
so before hitting the return address check what all other threads are doing in your app set an appropriate break on threads of interest and hit the return when the other thread executes its quantum your break will get hit
You're looking at the wrong thread!
From the partial output you supplied seems like you're attaching to a running process (rather than start it from the debugger). To break into a running process the debugger injects a thread into the target process that basically contains a hardcoded int 3 instruction and not much more.
It does it by calling ntdll!RtlpCreateUserThreadEx (the internal undocumented native parallel of CreateRemoteThread) supplying ntdll!DbgUiRemoteBreakin as the start address for the new thread.
The sole purpose of this synthetic thread is to generate the breakpoint exception. This exception causes the operating system to stop running the target process and passes control to the debugger. After it does this it's not needed anymore and it commits suicide.
What you're supposed to do at this point is probably switch to your thread of interest using ~s command, set breakpoints and then continue execution.
If try to step through this synthetic thread it will just end, and then the process will continue doing whatever it was doing before you broke into it, which is pretty much the opposite of what you want,
That's what this stack means:
00000000`0203fc38 00007ff9`fc86c63e ntdll!NtTerminateThread+0x14
00000000`0203fc40 00007ff9`fc8d903a ntdll!RtlExitUserThread+0x4e
00000000`0203fc80 00007ff9`fc86c5c5 ntdll!DbgUiRemoteBreakin+0x5a
00000000`0203fcb0 00000000`00000000 ntdll!RtlUserThreadStart+0x45
ntdll!RtlUserThreadStart is the real user-mode entry point of all user-mode threads and you can see that it just called ntdll!DbgUiRemoteBreakin after which you continued a bit until the thread finally ends itself.
I am working on the project where I communicate with another device over COM port.
For incoming data I am using VaComm1RXchar event, there I store the message into the array and increment msgIndex which represents number of messages.
Then I call the function where I work with this message.
Inside this function is this timeout cycle where I wait for this message:
while MsgIndex < 1 do
begin
stop := GetTickCount;
if (stop - start)> timeout then
begin
MessageBox(0, 'Timeout komunikace !', 'Komunikace', MB_OK);
exit(false);
end;
sleep(10);
end;
The strange thing for me is that, when have it like this above then it always end with timeout. But when I put on there before this while cycle a ShowMessage('Waiting') then It works correcly.
Does anyone know what can caused this and how can I solve it? Thanks in advance!
We can deduce that the VaComm1RXchar event is a synchronous event and that by blocking your program in a loop you are preventing the normal message processing that would allow that event to execute.
Showing a modal dialog box, on the other hand, passes message handling to that dialog so the message queue is properly serviced and your Rx events and handled normally.
You can be certain this is the case if this also works (please never write code like this - it's just to prove the point):
while MsgIndex < 1 do begin
stop := GetTickCount;
if (stop - start)> timeout then begin
MessageBox(0, 'Timeout komunikace !', 'Komunikace', MB_OK);
exit(false);
end;
Application.ProcessMessages; // service the message queue so that
sleep(10); // your Rx event can be handled
end;
If there is a lesson here it is that RS-232 communication really needs to be done on a background thread. Most all implementations of "some chars have been received" events lead to dreadful code for the very reason you are discovering. Your main thread needs to be free to process the message that characters have been received but, at the same time, you must have some parallel process that is waiting for those received characters to complete a cogent instruction. There does not exist a sensible solution in an event-driven program to both manage the user interface and the communication port at the same time on one thread.
A set of components like AsyncPro**, for example, wrap this functionality into data packets where synchronous events are used but where the components manage start and end string (or bytes) detection for you on a worker thread. This removes one level of polling from the main thread (ie: you always get an event when a complete data packet has arrived, not a partial one). Alternatively, you can move the communication work to a custom thread and manage this yourself.
In either case, this is only partly a solution, of course, since you still cannot stick to writing long procedural methods in synchronous event handlers that require waiting for com traffic. The second level of polling, which is managing a sequence of complete instructions, will still have you needing to pump the message queue if your single procedure needs to react to a sequence of more than one comport instruction. What you also need to think about is breaking up your long methods into shorter pieces, each in response to specific device messages.
Alternatively, for heavily procedural process automation, it is also often a good idea to move that work to a background thread as well. This way your worker threads can block on synchronization objects (or poll in busy loops for status updates) while they wait for events from hardware. One thread can manage low level comport traffic, parsing and relaying those commands or data packets, while a second thread can manage the higher level process which is handling the sequence of complete comport instructions that make up your larger process. The main thread should primarily only be responsible for marshalling these messages between the workers, not doing any of the waiting itself.
See also : I do not understand what Application.ProcessMessages in Delphi is doing
** VAComm may also support something like this, I don't know. The API and documentation are not publicly available from TMS for ASync32 so you'll need to consult your local documentation.
What happens is that a modal message loop executes when the dialog is showing. That this message loop changes behaviour for you indicates that your communications with the device require the presence of a message loop.
So the solution for you is to service the message queue. A call to Application.ProcessMessages in your loop will do that, but also creates other problems. Like making your UI become re-entrant.
Without knowing more about your program, I cannot offer more detailed advice as to how you should solve this problem.
My application works as follows:
the worker-threads initialize and begin waiting in pthread_cond_wait()
the main thread connects to DB and starts handing over one row at a time to the proper worker
Because of the DB-driver internals, the next row can not be read until the current one is extracted, so the main thread has to wait for the worker to "accept" the row.
I achieve this by calling pthread_cond_wait() inside the main thread -- waiting for a pthread_signal() from the worker. This works cleanly -- on both Linux and FreeBSD -- but usually takes much longer on Linux. Whereas I consistently process the entire 1.6M rows in about 27 seconds on FreeBSD, on Linux it usually takes over 2 minutes. Except sometimes the Linux box shows the same time...
The code is compiled from the same source and the program talks to the same DB-server. If anything, the Linux box is located on the same LAN as the DB, whereas the FreeBSD machine connects via VPN (so it should be a bit slower). But it is the wide inconsistency of the Linux results that bothers me, and I suspect the thread-coordination...
Here is what I have now:
MAIN THREAD WORKER
--------------------------------------------------------------------------
get new row
figure out, which worker it belongs to lock my mutex
lock the worker's mutex go into pthread_cond_wait
signal the worker extract the row's data
unlock the worker's mutex signal the main thread
go into pthread_cond_wait unlock the mutex
go on back to getting the next row go on to process the row's data
Is there a better way? Thanks!
If reading the next row must be serial anyway, why are you delegating this to the worker? As the main thread has to wait anyway, have the main thread do the extraction and have the hand-off occur as soon as the row has been sufficiently extracted that the master can proceed to the next row.
Other than that, you will need to provide code, as your description is incomplete, as would be any question of this nature submitted without code.
It looks like your problem is that you are calling pthread_cond_wait() without the mutex locked in the main thread. This means that there's a race-condition: if the worker thread wakes up, extracts the data and signals the condition before the parent executes pthread_cond_wait(), the wakeup will be lost.
What you should have is some shared state paired with the condition variable, like this:
Main Thread:
get_new_row();
worker = decide_worker();
pthread_mutex_lock(&mutex);
/* Signal worker that data is available */
flag[worker] = 1;
pthread_cond_signal(&cond);
/* Wait for worker to extract it */
while (flag[worker] == 1)
pthread_cond_wait(&cond, &mutex):
pthread_mutex_unlock(&mutex);
Worker Thread:
pthread_mutex_lock(&mutex);
/* Wait for data to be available */
while (flag[worker] == 0)
pthread_cond_wait(&cond, &mutex):
extract_row_data();
/* Signal main thread that extraction is complete */
flag[worker] = 0;
pthread_cond_signal(&cond);
pthread_mutex_unlock(&mutex);
We need to Start a thread into a service application we developed.
We did in the OnExecute event, and it failed, and later we did in the OnStart event, and it failed again. Maybe we have to do something else to start the thread.
The line of code we only have to type is MonitorThread.Start;
Where and how we can to start the thread??
Thanks.
On the face of it, starting a thread in a service is no different from starting a thread in any other kind of application. Simply instantiate the thread object and let it run. If you created the object in a suspended state, then call Start on it (or, in versions earlier than 2010, Resume).
MonitorThread := TMonitorThread.Create;
MonitorThread.Start; // or MonitorThread.Resume
If that doesn't work, then you need to take a closer look at exactly what doesn't work. Examine exception messages and return codes. Use the debugger to narrow things down.
If it's possible, I advise you to not create the thread suspended. Instead, just provide the object all the parameters it needs in its constructor. Let it initialize itself, and it will start running just before the constructor returns to the caller. No need for additional thread management outside the thread object.