I'd like to attach gdb to a process where I can't easily control the startup of the process because it is run from inetd and where the process completes too fast to be able to attach to it once it starts.
What I'd like to do is insert a bit of code at the particular point that I want to start debugging. That code would ideally wait for the debugger to attach and then continue. I've tried with a sleep but it is then tricky to choose a delay long enough that I have time to catch it but short enough not to be a nuisance waiting for it to elapse after gdb is attached.
Is there any better choices of code to insert or to call for this purpose?
What I'd like to do is insert a bit of code at the particular point that I want to start debugging.
I usually do it like this:
volatile int done = 0;
while (!done) sleep(1);
Attach GDB (you'll be inside sleep). Do finish, then set var done = 1, and enjoy the rest of your debugging session ;-)
using namespace std;
using namespace std::this_thread;
using namespace chrono;
void waitForDebugger()
{
steady_clock::time_point tp1, tp2, tp3;
microseconds d1 = microseconds(10000);
microseconds d2 = microseconds(20000);
bool looped = false;
while (true)
{
sleep_for(d1);
tp1 = steady_clock::now();
if (looped && duration_cast<microseconds>(tp1 - tp3) > d2)
{
break;
}
sleep_for(d1);
tp2 = steady_clock::now();
if (looped && duration_cast<microseconds>(tp2 - tp1) > d2)
{
break;
}
sleep_for(d1);
tp3 = steady_clock::now();
if (looped && duration_cast<microseconds>(tp3 - tp2) > d2)
{
break;
}
looped = true;
}
}
Related
int main()
{
int count = 0;
int pid;
if ( !(pid=fork()))
{
while (((count<2) && (pid=fork()) ) {
count++;
printf("%d",count)
}
if(count>0)
{
printf("%d", count);
}
}
if (pid) {
waitpid(pid,NULL,0);
count = count<<1;
printf("%d", count)
}
}
I'm having trouble reading this piece of code. I can't figure out how many system calls are made or even remotely trace them. This is leading me to not be able to understand how the output works. I am assuming the scheduler can do anything. What are all possible outputs and how many system calls are made?
Launch with strace -f ./myprogram to trace all system calls.
From looking at the code, about 3 additional processes will be created.
I have a pretty complicated OpenCL app. It fires up 5 different contexts on 5 different GPUs, and executes the same kernel on all of them, splitting up the work into 1024 "chunks" to be processed.
Each time a kernel finishes, a result is checked for, and it's given a new chunk. Sometimes, when running, as the app is starting (very rarely mid-run) it will immediately segfault on the GetEventInfo call.
This is done in a loop using callbacks and clGetEventInfo calls to ensure something is finished before moving on to the next step.
GDB output:
(gdb) back
#0 0x00007fdc686ab525 in clGetEventInfo () from /usr/lib/libOpenCL.so.1
#1 0x00000000004018c1 in ready (event=0x26a00000267) at gputest.c:165
#2 0x0000000000404b5a in main (argc=9, argv=0x7fffdfe3b268) at gputest.c:544
The ready function:
int ready(cl_event event) {
int rdy;
if(!event)
return 0;
clGetEventInfo(event, CL_EVENT_COMMAND_EXECUTION_STATUS, sizeof(cl_int), &rdy, NULL);
if(rdy == CL_COMPLETE)
return 1;
return 0;
}
How the kernel is run, the event set, and checked. Some pseudocode inserted for brevity:
while(test if loop is complete) {
for(j = 0; j < GPUS; j++) {
if(gpu[j].waiting && loops < 9999) {
gpu[j].waiting = 0;
offset[j] = loops * 1024 * 1024;
loops++;
EC("kernel init", clEnqueueNDRangeKernel(queues[j], kernel_init[j], 1, &(offset[j]), &global_work_size, &work128, 0, NULL, &events[j]));
gpu[j].readsearch = events[j];
gpu[j].reading = 1;
}
}
for(j = 0; j < GPUS; j++) {
if(gpu[j].reading && ready(gpu[j].readsearch)) {
gpu[j].reading = 0;
gpu[j].waiting = 1;
// unrelated reporting other code here
}
}
}
Its pretty simple. There is more to the code, but it's unrelated. The ready/checking function is very simple. I even added debugging to the ready function to printf the event # to see what was happening when it crashed - nothing really. No pattern I could see.
What could be causing this?
Ugh. Found the problem. Since you cannot initialize values when you create/declare a struct, I was using some values uninitialized. I malloc'ed the gpu structs then just started using them. With if(gpu[x].reading &&...) being random data and completely uninitialized. So sometimes it was non-zero, which allowed the ready() function to fire off. Since the gpu[x].readsearch event was never set in the first place, clGetEventInfo bombed trying to use whatever was at the memory location.
This would be time number 482,847 that accidentally using uninitialized variables has burned me.
Trying to make simon says game as my semester project, problem is I cant add a delay between the colors when they change,
i.e i want to add a delay so that when one box color changes, then after about 3~4 seconds the next box color changes, but the problem is when I put the Sleep() in my for loop, the system pauses for the amount given as a whole, then displays all the colors changed at the same time not one by one....
Any help, here is the function that i call when the game's start button is clicked. How to fix it ?
void flash()
{
srand(time(NULL));
int x;
for (int i = 5; i > 0;i--)
{
x = rand() % 4;
if (x == 0)
{
button1->BackColor = System::Drawing::Color::Blue;
}
else if (x == 1)
{
button2->BackColor = System::Drawing::Color::Blue;
}
else if (x == 2)
{
button3->BackColor = System::Drawing::Color::Blue;
}
else if (x == 3)
{
button4->BackColor = System::Drawing::Color::Blue;
}
Sleep(500);
}
}
P.s I have tried to put the sleep in the if statements but that doesn't work either, Any help please ?
As your code is single-treaded and you are updating the colors of the buttons in a loop, there is (currently) no chance for the application's standard drawing routines to kick in, until the loop is finished. If you do want a redraw while being in the loop, you have to manually issue it by (e.g.):
button1->Invalidate();
button1->Update();
Please be aware that, if you stay in the loop for too long, windows does recognize that your application is not responding to windows messages and renders it "unresponsive" (window fading to half white). To circumvent this, you can use the Timer class from System::Windows::Forms to implement the delay behaviour.
Can someone please tell me how to go about creating a maximum of N instances of an application in MFC?
Also, if N instances are running, and one instance gets closed, then one new instance can be created (but no more than N instances can run at any one time).
Thank you in advance.
a.
You can create a global semaphore that up to n process instances can enter. The n+1 th instance of your process will fail to enter the semaphore. Of course you should select a short timeout for the locking operation so you can present a meaningful feedback to the user.
For the semaphore stuff you can take a look at MSDN.
I'd use lock files. In your CMyApp::InitInstance() add:
CString Path;
// better get the path to the global app data or local user app data folder,
// depending on if you want to allow the three instances machine-wide or per user.
// Windows' file system virtualization will make GetModuleFileName() per user:
DWORD dw = GetModuleFileName(m_hInstance,
Path.GetBuffer(MAX_PATH), MAX_PATH);
Path.ReleaseBuffer();
// strip "exe" from filename and replace it with "lock"
Path = Path.Left(Path.GetLength()-3) + T("lock");
int i;
// better have the locking file in your class and do a clean Close on ExitInstance()!
CFile *pLockingFile = NULL;
for (i = 0; i < 3; i++) // restrict to three instances
{
CString Counter;
Counter.Format(T("%d"), i);
TRY
{
pLockingFile = new CFile(Path + Counter,
CFile::modeCreate|CFile::modeWrite|CFile::shareExclusive);
pLockingFile.Close();
break; // got an instance slot
}
CATCH( CFileException, e )
{
// maybe do something else here, if file open fails
}
END_CATCH
if (i >= 3)
return TRUE; // close instance, no slot available
}
Edit: To lock the software machine-wide, retrieve the common app folder using the following function instead of calling GetModuleFileName().
#pragma warning(disable: 4996) // no risk, no fun
BOOL GetCommonAppDataPath(char *path)
{
*path = '\0';
if (SHGetSpecialFolderPath(NULL, path, CSIDL_COMMON_APPDATA, TRUE))
{
strcat(path, T("\\MyApplication")); // usually found under C:\ProgramData\MyApplication
DWORD dwFileStat = GetFileAttributes(path);
if (dwFileStat == 0xffffffff) // no MyApplication directory yet?
CreateDirectory(path, NULL); // create it
dwFileStat = GetFileAttributes(path); // 2nd try, just to be sure
if (dwFileStat == 0xffffffff || !(dwFileStat & FILE_ATTRIBUTE_DIRECTORY))
return FALSE;
return TRUE;
}
return FALSE;
}
Note: This will only work from Vista on. If you have XP, writing to a global directory is an easy task, e.g. C:\Windows\Temp. I have put the function in a helper dll I only load if the OS is Vista or higher. Otherwise your software won't start because of unresolved references in system dlls.
I'm building a simple game in SDL. I've been through countless tutorials and I've clearly missed something as it still ignoring my Joystick completely
In my constructor
SDL_JoystickEventState(SDL_ENABLE);
joystick = SDL_JoystickOpen(0);
In my update I'm calling a test to check I have actually initialized the joystick
if (SDL_NumJoysticks() <= 0)
{
done = true;
}
Here is my player update as well
void World::playerMovement()
{
SDL_Event event;
while (SDL_PollEvent (&event))
{
switch (event.type)
{
case SDL_QUIT:
done = true;
break;
case SDL_JOYAXISMOTION:
if ( ( event.jaxis.value < -3200 ) || (event.jaxis.value > 3200 ) )
{
test = true;
}
break;
}
}
}
Test is simply a bool which once true will mean my enemies start spawning. I also run a check in main
if (SDL_Init( SDL_INIT_VIDEO | SDL_INIT_JOYSTICK ) < 0)
{
fprintf(stderr, "Couldn't initialize SDL: %s\n", SDL_GetError());
done = true;
}
When I run the game it loads as normal but no matter how much I move the joystick it won't set test to true.
I also tried using the following in the while poll event loop instead.
if (event.type == SDL_JOYAXISMOTION)
{
if(SDL_JoystickGetAxis(joystick, 1) > 0)
{
test = true;
}
}
Any idea's what I have missed?
I think emartel has the best answer to make sure SDL_joystick is working.
When does World::playerMovement() happen? The overall flow of your program is hard to determine from these snippets.
I'm happy to share with you my code for handling joysticks, which keeps track of: multiple joysticks, axes scaled [-1,1] with deadzone removed, and buttons held down.
http://www.raptor007.com/code/RaptorEngine_Joystick.zip
And here's a snippet of how that would be utilized as part of your main loop:
// FIXME: SDL needs to be initialized before we get here.
JoystickManager Joy;
Joy.Initialize();
double deadzone = 0.02;
// Main loop.
bool done = false;
while( ! done )
{
// Keep the list of joysticks up-to-date.
Joy.FindJoysticks();
// Handle all user input.
SDL_Event event;
while( SDL_PollEvent( &event ) )
{
// Let the JoystickManager track events relevant to it.
Joy.TrackEvent( &event );
// FIXME: Handle single-press events here (next target, etc).
// Don't handle button-held-down events like firing (see below).
if( event.type == SDL_QUIT )
done = true;
}
// Read joystick 0 analog axes.
double roll = Joy.Axis( 0, 0, deadzone );
double pitch = Joy.Axis( 0, 1, deadzone );
double yaw = Joy.Axis( 0, 3, deadzone );
double throttle = Joy.AxisScaled( 0, 2, 1., 0., 0., deadzone );
// Read joystick 0 buttons held down.
bool firing = Joy.ButtonDown( 0, 0 );
// FIXME: Update game objects and draw graphics.
}
I found a weird behaviour in SDL2:
If no events are put into the queue, try adding the following before the SDL_Init call:
SDL_SetHint(SDL_HINT_JOYSTICK_ALLOW_BACKGROUND_EVENTS,"1");
Are you sure joystick points to a valid joystick?
You state that you're getting it in your Constructor... does that contructor happen to be called before you initialize SDL with SDL_INIT_JOYSTICK? This could happen if your player is a global variable.
Make sure that in order you:
Init the Joystick subsystem, either by adding it to your SDL_Init with | SDL_INIT_JOYSTICK or by calling SDL_InitSubSystem(SDL_INIT_JOYSTICK);
Check SDL_NumJoysticks() > 0
Get joystick 0: joystick = SDL_JoystickOpen(0);
Enable events: SDL_JoystickEventState(SDL_ENABLE);
Process your events with SDL_PollEvent
At the end of your program, close your joystick: SDL_JoystickClose(joystick);
Also, make sure the joystick is properly detected in Windows and reports its inputs properly.
Looks like your SDL isn't init proper.
replace
SDL_Init(SDL_INIT_VIDEO | SDL_INIT_JOYSTICK)
with
SDL_Init(SDL_INIT_EVERYTHING)
Is this SDL 1.2 or 2.0? In my case, on 2.0 SDL_PollEvent(&event) didn't actually put any data in the event struct. After that call, I had to use SDL_JoystickGetAxis(joystick_id, axis) and friends to get data.
So in your case, try to move the SDL_JoystickGetAxis call out of the if-test on event-type.
If you call SDL_NumJoysticks to get the number of controllers connected, then call SDL_JoystickOpen which returns a joystick identifier before your game loop then you will receive the SDL_JOYAXISMOTION events.
e.g.
int num_joy;
num_joy = SDL_NumJoysticks();
printf("%d joysticks found\n", num_joy);
for(int i = 0; i < num_joy; i++)
{
SDL_Joystick *joystick = SDL_JoystickOpen(i);
printf("Joystick name: %s\n", SDL_JoystickName(joystick));
}
SDL_Event event;
bool quit = false;
// Game loop
while(!quit)
{
// event loop
while(SDL_PollEvent(&event))
{
if (event.type == SDL_JOYAXISMOTION)
{
printf("Joystick______EVENT!\n");
}
// etc.....
See https://wiki.libsdl.org/SDL_JoystickName
I do not know how this can help you, but I do know that pygame supports joystick. And pygame is the python port of the SDL library. If everything fails, I guess you can always write that particular piece of code in python.