I used one of the minimise to tray VC++ examples to create a program that would pop up a message at intervals to remind me to rest my eyes.
The program goes like this:
startTime = time(0);
g_hInstance=hInstance;
HWND hWnd=CreateDialog(hInstance,MAKEINTRESOURCE(IDD_DIALOG1),NULL,DialogProc);
if(hWnd)
{
MSG msg;
_beginthread(&checkEyeRestTime, 0, 0);
while(GetMessage(&msg,hWnd,0,0))
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
}
and the checkEyeRestTime function:
void checkEyeRestTime(void* ptr)
{
while( true )
{
//logic to check time and display message
}//while
_endthread();
}
But this program takes up 50% CPU on a two core processor. How can I reduce the load on the processor?
Or insert Sleep(0) in the thread. This allows other threads to get some time.
If this does not help, you can increase sleep time.
Use a timer event instead of the polling loop.
Related
I'm currently trying to make my device (STM32F105) which is usually running 12 threads on CMSIS RTOS go to low power mode. In order to simplify the algorythm I think (definitely not sure) that it's a good idea to terminate all the threads using osThreadTerminate and after a wake up recreate them using osThreadCreate
void os_idle_demon (void) {
/* The idle demon is a system thread, running when no other thread is */
/* ready to run. */
for (;;) {
/* HERE: include optional user code to be executed when no thread runs.*/
if (Sleep.SleepEnabled == 1)
{
if (Sleep.IsSleeping == 1)
{
// __wfi();
// PWR_EnterSTOPMode(PWR_Regulator_ON, PWR_STOPEntry_WFI); //PWR_Regulator_LowPower
__nop();
// osDelay(5000);
if (Sleep.WakeUp)
{
Sleep.IsSleeping = 0;
WakeUp();
// SetSysClock();
Sleep.WakeUp = 0;
Sleep.SleepEnabled = 0;
Sleep.TimeTillSleep = 60;
}
}
else
{
if (Sleep.TimeTillSleep == 0 )
{
TerminateTasks();
ResetPeripherals();
Sleep.IsSleeping = 1;
// PWR_EnterSTANDBYMode();
// __wfi();
// PWR_EnterSTOPMode(PWR_Regulator_ON, PWR_STOPEntry_WFI);
__nop();
// osDelay(5000);
}
}
}
}
}
As you can see I use some global variables to determinte when to sleep. TerminateTasks(); is used to terminate all of my running threads using osThreadTerminate function which doesn't seem to cause any trouble, but after I call WakeUp(); which uses osThreadCreate function to recreate terminated threads I run into an os stack overflow. So there are a few questions I struggle to find answers to. Does osThreadTerminate command in CMSIS-RTOS release stack after execution? Is there a better way to go into a low power mode ? I hope I made my point clear, if there's a need to be more specific let me know. Would be grateful if you shared your experience with similar problems.
Do you use dynamic allocation in your other thread ? Because if so, killing your thread when there are running could result in memory leak.
I have N threads performing various task and these threads must be regularly synchronized with a thread barrier as illustrated below with 3 thread and 8 tasks. The || indicates the temporal barrier, all threads have to wait until the completion of 8 tasks before starting again.
Thread#1 |----task1--|---task6---|---wait-----||-taskB--| ...
Thread#2 |--task2--|---task5--|-------taskE---||----taskA--| ...
Thread#3 |-task3-|---task4--|-taskG--|--wait--||-taskC-|---taskD ...
I couldn’t find a workable solution, thought the little book of Semaphores http://greenteapress.com/semaphores/index.html was inspiring. I came up with a solution using std::atomic shown below which “seems” to be working using three std::atomic.
I am worried about my code breaking down on corner cases hence the quoted verb. So can you share advise on verification of such code? Do you have a simpler fool proof code available?
std::atomic<int> barrier1(0);
std::atomic<int> barrier2(0);
std::atomic<int> barrier3(0);
void my_thread()
{
while(1) {
// pop task from queue
...
// and execute task
switch(task.id()) {
case TaskID::Barrier:
barrier2.store(0);
barrier1++;
while (barrier1.load() != NUM_THREAD) {
std::this_thread::yield();
}
barrier3.store(0);
barrier2++;
while (barrier2.load() != NUM_THREAD) {
std::this_thread::yield();
}
barrier1.store(0);
barrier3++;
while (barrier3.load() != NUM_THREAD) {
std::this_thread::yield();
}
break;
case TaskID::Task1:
...
}
}
}
Boost offers a barrier implementation as an extension to the C++11 standard thread library. If using Boost is an option, you should look no further than that.
If you have to rely on standard library facilities, you can roll your own implementation based on std::mutex and std::condition_variable without too much of a hassle.
class Barrier {
int wait_count;
int const target_wait_count;
std::mutex mtx;
std::condition_variable cond_var;
Barrier(int threads_to_wait_for)
: wait_count(0), target_wait_count(threads_to_wait_for) {}
void wait() {
std::unique_lock<std::mutex> lk(mtx);
++wait_count;
if(wait_count != target_wait_count) {
// not all threads have arrived yet; go to sleep until they do
cond_var.wait(lk,
[this]() { return wait_count == target_wait_count; });
} else {
// we are the last thread to arrive; wake the others and go on
cond_var.notify_all();
}
// note that if you want to reuse the barrier, you will have to
// reset wait_count to 0 now before calling wait again
// if you do this, be aware that the reset must be synchronized with
// threads that are still stuck in the wait
}
};
This implementation has the advantage over your atomics-based solution that threads waiting in condition_variable::wait should get send to sleep by your operating system's scheduler, so you don't block CPU cores by having waiting threads spin on the barrier.
A few words on resetting the barrier: The simplest solution is to just have a separate reset() method and have the user ensure that reset and wait are never invoked concurrently. But in many use cases, this is not easy to achieve for the user.
For a self-resetting barrier, you have to consider races on the wait count: If the wait count is reset before the last thread returned from wait, some threads might get stuck in the barrier. A clever solution here is to not have the terminating condition depend on the wait count variable itself. Instead you introduce a second counter, that is only increased by the thread calling the notify. The other threads then observe that counter for changes to determine whether to exit the wait:
void wait() {
std::unique_lock<std::mutex> lk(mtx);
unsigned int const current_wait_cycle = m_inter_wait_count;
++wait_count;
if(wait_count != target_wait_count) {
// wait condition must not depend on wait_count
cond_var.wait(lk,
[this, current_wait_cycle]() {
return m_inter_wait_count != current_wait_cycle;
});
} else {
// increasing the second counter allows waiting threads to exit
++m_inter_wait_count;
cond_var.notify_all();
}
}
This solution is correct under the (very reasonable) assumption that all threads leave the wait before the inter_wait_count overflows.
With atomic variables, using three of them for a barrier is simply overkill that only serves to complicate the issue. You know the number of threads, so you can simply atomically increment a single counter every time a thread enters the barrier, and then spin until the counter becomes greater or equal to N. Something like this:
void barrier(int N) {
static std::atomic<unsigned int> gCounter = 0;
gCounter++;
while((int)(gCounter - N) < 0) std::this_thread::yield();
}
If you don't have more threads than CPU cores and a short expected waiting time, you might want to remove the call to std::this_thread::yield(). This call is likely to be really expensive (more than a microsecond, I'd wager, but I haven't measured it). Depending on the size of your tasks, this may be significant.
If you want to do repeated barriers, just increment the N as you go:
unsigned int lastBarrier = 0;
while(1) {
switch(task.id()) {
case TaskID::Barrier:
barrier(lastBarrier += processCount);
break;
}
}
I would like to point out that in the solution given by #ComicSansMS ,
wait_count should be reset to 0 before executing cond_var.notify_all();
This is because when the barrier is called a second time the if condition will always fail, if wait_count is not reset to 0.
I have a main thread which creates another thread to perform some job.
main thread has a reference to that thread. How do I kill that thread forcefully some time later, even if thread is still operating. I cant find a proper function call that does that.
any help would be appreciable.
The original problem that I want to solve is I created a thread a thread to perform a CPU bound operation that may take 1 second to complete or may be 10 hours. I cant predict how much time it is going to take. If it is taking too much time, I want it to gracefully abandon the job when/ if I want. can I somehow communicate this message to that thread??
Assuming you're talking about a GLib.Thread, you can't. Even if you could, you probably wouldn't want to, since you would likely end up leaking a significant amount of memory.
What you're supposed to do is request that the thread kill itself. Generally this is done by using a variable to indicate whether or not it has been requested that the operation stop at the earliest opportunity. GLib.Cancellable is designed for this purpose, and it integrates with the I/O operations in GIO.
Example:
private static int main (string[] args) {
GLib.Cancellable cancellable = new GLib.Cancellable ();
new GLib.Thread<int> (null, () => {
try {
for ( int i = 0 ; i < 16 ; i++ ) {
cancellable.set_error_if_cancelled ();
GLib.debug ("%d", i);
GLib.Thread.usleep ((ulong) GLib.TimeSpan.MILLISECOND * 100);
}
return 0;
} catch ( GLib.Error e ) {
GLib.warning (e.message);
return -1;
}
});
GLib.Thread.usleep ((ulong) GLib.TimeSpan.SECOND);
cancellable.cancel ();
/* Make sure the thread has some time to cancel. In an application
* with a UI you probably wouldn't need to do this artificially,
* since the entire application probably wouldn't exit immediately
* after cancelling the thread (otherwise why bother cancelling the
* thread? Just exit the program) */
GLib.Thread.usleep ((ulong) GLib.TimeSpan.MILLISECOND * 150);
return 0;
}
I am learning about threading and multithreading..so i just created a small application in which i will update
the progressbar and a static text using threading.I vl get two inputs from the user, start and end values
for how long the loop should rotate.I have 2threads in my application.
Thread1- to update the progressbar(according to the loop) the static text which will show the count(loop count).
Thread2 - to update the another static text which will just diplay a name
Basically if the user clicks start, the progressbar steps up and at the same time filecount and the name are displayed parallely.
There's is another operation where if the user clicks pause it(thread) has to suspend until the user clicks resume.
The problem is,the above will not work(will not suspend and resume) for both thread..but works for a singlw thread.
Please check the code to get an idea and reply me what can done!
on button click start
void CThreadingEx3Dlg::OnBnClickedStart()
{
m_ProgressBar.SetRange(start,end);
myThread1 = AfxBeginThread((AFX_THREADPROC)MyThreadFunction1,this);
myThread2 = AfxBeginThread((AFX_THREADPROC)MyThreadFunction2,this);
}
thread1
UINT MyThreadFunction1(LPARAM lparam)
{
CThreadingEx3Dlg* pthis = (CThreadingEx3Dlg*)lparam;
for(int intvalue =pthis->start;intvalue<=pthis->end; ++intvalue)
{
pthis->SendMessage(WM_MY_THREAD_MESSAGE1,intvalue);
}
return 0;
}
thread1 function
LRESULT CThreadingEx3Dlg::OnThreadMessage1(WPARAM wparam,LPARAM lparam)
{
int nProgress= (int)wparam;
m_ProgressBar.SetPos(nProgress);
CString strStatus;
strStatus.Format(L"Thread1:Processing item: %d", nProgress);
m_Static.SetWindowText(strStatus);
Sleep(100);
return 0;
}
thread2
UINT MyThreadFunction2(LPARAM lparam)
{
CThreadingEx3Dlg* pthis = (CThreadingEx3Dlg*)lparam;
for(int i =pthis->start;i<=pthis->end;i++)
{
pthis->SendMessage(WM_MY_THREAD_MESSAGE2,i);
}
return 0;
}
thread2 function
LRESULT CThreadingEx3Dlg::OnThreadMessage2(WPARAM wparam,LPARAM lparam)
{
m_Static1.GetDlgItem(IDC_STATIC6);
m_Static1.SetWindowTextW(L"Thread2 Running");
Sleep(100);
m_Static1.SetWindowTextW(L"");
Sleep(100);
return TRUE;
}
void CThreadingEx3Dlg::OnBnClickedPause()
{
// TODO: Add your control notification handler code here
if(!m_Track)
{
m_Track = TRUE;
GetDlgItem(IDCANCEL)->SetWindowTextW(L"Resume");
myThread1->SuspendThread();
WaitForSingleObject(myThread1->m_hThread,INFINITE);
myThread2->SuspendThread();
m_Static.SetWindowTextW(L"Paused..");
}
else
{
m_Track = FALSE;
GetDlgItem(IDCANCEL)->SetWindowTextW(L"Pause");
myThread1->ResumeThread();
myThread2->ResumeThread();
/*myEventHandler.SetEvent();
WaitForSingleObject(myThread1->m_hThread,INFINITE);*/
}
}
I thought I should summarize some of the discussion in the comments into an answer.
In Windows programming, you should never try to manipulate a GUI control from a background thread, as doing so can cause your program to deadlock . This means only the main thread should ever touch elements of the GUI. (Technically, what matters is which thread created the control, but it's not common to create controls in background threads).
This requirement is detailed in Joe Newcomer's article on worker threads (see "Worker Threads and the GUI II: Don't Touch the GUI").
You are using SendMessage in your thread procedures. This causes the appropriate message handler for the target control to be invoked, but in the thread that called SendMessage. In your case, that means the background threads run the message handlers and therefore update the progress bar and label.
The alternative is to use PostMessage. This causes the message to be added to a queue to be processed by the main thread's message loop. When the main thread gets to run, it processes the messages in the order they were added to the queue, calling the message handlers itself. Since the main thread owns the windows, it is safe for it to update the controls.
You should also beware that SuspendThread and ResumeThread are tricky to get right. You might want to read this section of Joe Newcomer's article, which describes some of the dangers.
Tasks like this are often better achieved by using a timer. This is a mechanism for having the operating system notify your program when a particular amount of time has passed. You could implement this with a timer as below:
BEGIN_MESSAGE_MAP(CThreadingEx3Dlg, CDialog)
ON_WM_DESTROY()
ON_WM_TIMER()
END_MESSAGE_MAP()
void CThreadingEx3Dlg::OnTimer(UINT_PTR nTimerID)
{
static int progress = 0;
if (nTimerID == 1)
{
m_ProgressBar.SetPos(progress);
CString strStatus;
strStatus.Format(_T("Processing item: %d"), progress);
m_Static.SetWindowText(strStatus);
progress++;
if (progress > end) // If we've reached the end of the updates.
KillTimer(1);
}
}
BOOL CThreadingEx3Dlg::OnInitDialog()
{
// ... initialize controls, etc, as necessary.
SetTimer(1, 100, 0);
}
void CThreadingEx3Dlg::OnDestroy()
{
KillTimer(1);
}
If you want both updates handled at the same time, they can use the same timer. If they need to happen at different times (such as one at a 100 ms interval and another at a 150 ms interval) then you can call SetTimer twice with different IDs. To pause the action, call KillTimer. To resume it, call SetTimer again.
Multi-threading and message queuing is quite a complex game. When you SendMessage from ThreadA to the same thread then it just calls the message handler. If you do it from ThreadA to another thread (ThreadB) then it gets more complicated. ThreadA then posts a message to the ThreadB's message queue and waits on a signal to say that ThreadB has finished processing the message and sent the return value. This raises an instant problem. If ThreadB is not pumping messages then you have a deadlock as the message in ThreadB's will never get "dispatched". This also raises an EVEN bigger problem. If ThreadB's message needs to send a message to a control created in ThreadA then you have a massive architectural problem. As ThreadA is currently suspended waiting for ThreadB to return and ThreadB is suspended waiting for ThreadA to return. Nothing will happen ... They will both sit suspended.
Thats about it really. Its pretty easy as long as you bear these issues in mind. ie It absoloutely IS possible despite what the others have said.
In general though your threading is pretty pointless because you straight away send a message to the main thread to do some processing. Why bother starting the threads in the first place. You may as well not bother because the threads will just sit there waiting for the main thread to return.
Why do you "WaitForSingleObject" anyway when you suspend the first thread? Why not just suspend them both.
All round, though, you aren't giving enough information about what you are doing to say exactly whats going on. What happens when you click pause, for example?
Windows will not operate properly when more than one thread interacts with the GUI. You'll need to reorganize your program so that does not happen.
I want to create a thread for some db writes that should not block the ui in case the db is not there. For synchronizing with the main thread, I'd like to use windows messages. The main thread sends the data to be written to the writer thread.
Sending is no problem, since CreateThread returns the handle of the newly created thread. I thought about creating a standard windows event loop for processing the messages. But how do I get a window procedure as a target for DispatchMessage without a window?
Standard windows event loop (from MSDN):
while( (bRet = GetMessage( &msg, NULL, 0, 0 )) != 0)
{
if (bRet == -1)
{
// handle the error and possibly exit
}
else
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
}
Why windows messages? Because they are fast (windows relies on them) and thread-safe. This case is also special as there is no need for the second thread to read any data. It just has to recieve data, write it to the DB and then wait for the next data to arrive. But that's just what the standard event loop does. GetMessage waits for the data, then the data is processed and everything starts again. There's even a defined signal for terminating the thread that is well understood - WM_QUIT.
Other synchronizing constructs block one of the threads every now and then (critical section, semaphore, mutex). As for the events mentioned in the comment - I don't know them.
It might seem contrary to common sense, but for messages that don't have windows, it's actually better to create a hidden window with your window proc than to manually filter the results of GetMessage() in a message pump.
The fact that you have an HWND means that as long as the right thread has a message pump going, the message is going to get routed somewhere. Consider that many functions, even internal Win32 ones, have their own message pumps (for example MessageBox()). And the code for MessageBox() isn't going to know to invoke your custom code after its GetMessage(), unless there's a window handle and window proc that DispatchMessage() will know about.
By creating a hidden window, you're covered by any message pump running in your thread, even if it isn't written by you.
EDIT: but don't just take my word for it, check these articles from Microsoft's Raymond Chen.
Thread messages are eaten by modal loops
Why do messages posted by PostThreadMessage disappear?
Why isn't there a SendThreadMessage function?
NOTE: Refer this code only when you don't need any sort of UI-related or some COM-related code. Other than such corner cases, this code works correctly: especially good for pure computation-bounded worker thread.
DispathMessage and TranslateMessage are not necessary if the thread is not having a window. So, simply just ignore it. HWND is nothing to do with your scenario. You don't actually need to create any Window at all. Note that that two *Message functions are needed to handle Windows-UI-related message such as WM_KEYDOWN and WM_PAINT.
I also prefer Windows Messages to synchronize and communicate between threads by using PostThreadMessage and GetMessage, or PeekMessage. I wanted to cut and paste from my code, but I'll just briefly sketch the idea.
#define WM_MY_THREAD_MESSAGE_X (WM_USER + 100)
#define WM_MY_THREAD_MESSAGE_Y (WM_USER + 100)
// Worker Thread: No Window in this thread
unsigned int CALLBACK WorkerThread(void* data)
{
// Get the master thread's ID
DWORD master_tid = ...;
while( (bRet = GetMessage( &msg, NULL, 0, 0 )) != 0)
{
if (bRet == -1)
{
// handle the error and possibly exit
}
else
{
if (msg.message == WM_MY_THREAD_MESSAGE_X)
{
// Do your task
// If you want to response,
PostThreadMessage(master_tid, WM_MY_THREAD_MESSAGE_X, ... ...);
}
//...
if (msg.message == WM_QUIT)
break;
}
}
return 0;
}
// In the Master Thread
//
// Spawn the worker thread
CreateThread( ... WorkerThread ... &worker_tid);
// Send message to worker thread
PostThreadMessage(worker_tid, WM_MY_THREAD_MESSAGE_X, ... ...);
// If you want the worker thread to quit
PostQuitMessage(worker_tid);
// If you want to receive message from the worker thread, it's simple
// You just need to write a message handler for WM_MY_THREAD_MESSAGE_X
LRESULT OnMyThreadMessage(WPARAM, LPARAM)
{
...
}
I'm a bit afraid that this is what you wanted. But, the code, I think, is very easy to understand. In general, a thread is created without having message queue. But, once Window-message related function is called, then the message queue for the thread is initialized. Please note that again no Window is necessary to post/receive Window messages.
You don't need a window procedure in your thread unless the thread has actual windows to manage. Once the thread has called Peek/GetMessage(), it already has the same message that a window procedure would receive, and thus can act on it immediately. Dispatching the message is only necessary when actual windows are involved. It is a good idea to dispatch any messages that you do not care about, in case other objects used by your thread have their own windows internally (ActiveX/COM does, for instance). For example:
while( (bRet = GetMessage(&msg, NULL, 0, 0)) != 0 )
{
if (bRet == -1)
{
// handle the error and possibly exit
}
else
{
switch( msg.message )
{
case ...: // process a message
...
break;
case ...: // process a message
...
break;
default: // everything else
TranslateMessage(&msg);
DispatchMessage(&msg);
break;
}
}
}