Compile Errors for CreateThread..

I have the following but getting compile errors...

Code:

---

void xboard(pcon)
{
for (;;) {
if (side == computer)
{
DWORD Id;
CreateThread(NULL, 0, (LPTHREAD_START_ROUTINE)think, pcon, 0, &Id);
...
}
...
...
}

void think(PVOID pArg)
{
PCON pcon = (PCON)pArg;
.....
.....
}

---

Inside my header file where I define all my functions, I have,

Code:

---

void think(PVOID pArg);

---

The errors I am getting are...

c:\documents and settings\gopi\desktop\chesscalc\protos.h(14) : error C2146: syntax error : missing ')' before identifier 'pArg'
c:\documents and settings\gopi\desktop\chesscalc\protos.h(14) : error C2061: syntax error : identifier 'pArg'
c:\documents and settings\gopi\desktop\chesscalc\protos.h(14) : error C2059: syntax error : ';'
c:\documents and settings\gopi\desktop\chesscalc\protos.h(14) : error C2059: syntax error : ')'
c:\documents and settings\gopi\desktop\chesscalc\chesscalc.c(53) : error C2065: 'think' : undeclared identifier
c:\documents and settings\gopi\desktop\chesscalc\search.c(133) : error C2198: 'ExitThread' : too few actual parameters

Ofcourse I am having #include <Windows.h> in files having xboard() and think() functions..
So please help me. Thanks.

If I get those errors I would try to do that

Code:

---

void xboard(PCON pcon)

---

Niara

I am really sorry its my typo mistake. Its already, void xboard(PCON pcon)

Cant help when you exclude all the code, you are basically missing a ) and perhaps a ; or two.

Hmm.. when compiling each and every file which is having #include "protos.h" its repeating those first 4 lines of errors I have posted above. Inside protos.h, I am having void think(PVOID pArg);

But I dont seem to have missed any ) or ; in it.
Anything wrong in it ?

Quote:

---

lpStartAddress

The starting address of the new thread. This is typically the address of a function declared with the WINAPI calling convention that accepts a single 32-bit pointer as an argument and returns a 32-bit exit code. Its prototype is:

DWORD WINAPI ThreadFunc( LPVOID );

---

Notice the prototype?

I changed it to as follows,
DWORD WINAPI think( LPVOID pArg )

But still getting an error as follows and other error I have posted above are also still there,
c:\documents and settings\gopi\desktop\chesscalc\protos.h(14) : error C2061: syntax error : identifier 'WINAPI'

Any suggestions please?

It would be easier to tell if you would post your complete code, or if that is fairly long, a short example that demonstrates the problem.

Code would be helpful.
Try without WINAPI.

Well, I got this answer for my explanation....

I asked:
Could anyone briefly tell how to create a multithreading in windows C for the below problem...

Code:

---

typedef struct tagCON {
BOOL fTimeout;
SEARCH_STATUS ss;
} CON, *PCON

int main()
{
char line[256], command[256];
static CON s_con;
PCON pcon = &s_con;

for(;;)
{
if(!fgets(line, 256, stdin))
return;
sscanf(line, "%s", command);

if(!strcmp(command, "go") {
think(pcon);
continue;
}
if(!strcmp(command, "quit") {
pcon->fTimeout = TRUE;
continue;
}

---

So I am calling think() from main and also passing a struct object. think() is basically executing for more than 10 mins...
What I want is, whenever user enters "quit", fTimeout is set to true, and inside think() for every millisec I am checking if fTimeout is true and if so, I will return to main.

But the problem is, since control is passed to think() from main, fgets() is not getting user input until control from think() is returned back to main. So how this can be achieved please?

Thanks in advance.

Someone replied
I don't think that you need threading for this. This is simple case when user waits for execution and optionally stops it - for such case, it is enough to test pressed key periodically. You can print something like this:
printf("Press Esc to stop\n");
think(...);

Inside think function, add the following code:

Code:

---

while (...)    // some loop - I guess you have it
{
    // calculations
    // ...

    if ( _getch() == 27 )          // Esc ?
        return;
}

---

I asked:
Well but I am not inputting them through keyboard.. There is a GUI interface through which commands like "quit", "go" etc are sent...
So I doubt, if I use _getch() inside think() will fetch the commands sent by GUI ?
Only in main() I can get right ?

Someone replied:
Is this console application or Winnows application? Looking at your main function I guess that this is console application. Do you have message loop?

I asked:
I am really sorry... I made a small mistake. Just replace that main() with xboard().
main() calls the above xboard(pcon).
ok?

Someone replied:
There are better ways to design the flow but.. you can just create a thread on yout think() function as follows:

Code:

---

void
think(PVOID pArg){
    while (1) {
        PCON pCon = (PCON)pArg;
        // keep think...ing...

        if (timeoutSet){
            ExitThread()
        }
    }
}


main(){
   
    for (;;;){
        // populate a new  struct arg from command fgets()..
        PCON pCon = new CON;

      If (command != "quit"){
          DWORD Id;
          CreateThread(NULL, 0, (LPTHREAD_START_ROUTINE )think, pCon, 0, &Id);
        } else {
            // set timeout flag
            // cleanup
            // break;
        }
    }

    // what else to do ?
}

---

Since the above is in another forum, I am not refering that link because I dont know if its legal as per the rules of this forum. Thanks.

Code:

---

void
think(PVOID pArg)

//...
CreateThread(NULL, 0, (LPTHREAD_START_ROUTINE )think, pCon, 0, &Id);

---

This isn't good. You shouldn't have to cast to LPTHREAD_START_ROUTINE. Declare your function with a DWORD return type.

Quote:

---

Do not declare this callback function with a void return type and cast the function pointer to LPTHREAD_START_ROUTINE when creating the thread. Code that does this is common, but it can crash on 64-bit Windows. (msdn)

---

If I've got this straight, you have a function ('think') that does some processing, and you want the user to be able to cancel the processing? Would something like this work?

Code:

---

#include <windows.h>
#include <iostream>



DWORD WINAPI Think(LPVOID lpParam)
{
 
  while (*(bool*)(lpParam))
  {
    std::cout<<"Thinking...";
  }
  return 0;
}



int main()
{

  bool start = true;
 
  HANDLE hThread = CreateThread(0,0,Think,&start,0,0);
  while (1)
  {
    if (GetAsyncKeyState(VK_ESCAPE))
    {
      start = false;
      break;
    }
  }

}

---

Well, but I need to pass pcon struct object to think() since I am doing some processing inside think().

Why isnt creating a thread as,

Code:

---

CreateThread(NULL, 0, think, (LPVOID)pcon, 0, &Id);

And think as,
DWORD WINAPI think( LPVOID pArg )
{
....
}

---

Why is the above throwing error ?
For your information,
static CON s_con;
PCON pcon = &s_con;

It should still work:

Code:

---

DWORD WINAPI Think(LPVOID lpParam)
{
  PCON pCon = (PCON)lpParam;
  while (!pCon->fTimeout)
  {
    //...
  }
  return 0;
}


CON s_con = {false,/*...*/};
 
CreateThread(0,0,Think,&s_con,0,&Id);
while (1)
  {
    if (GetAsyncKeyState(VK_ESCAPE))
    {
      s_con.fTimeout = true;
      break;
    }
  }

---

Ok, when I moved think() from seperate file to the file where main() and xboard() is there, its working.

But small problem with the logic...

Code:

---

void xboard(PCON pcon)
{
DWORD Id;
HANDLE hThread = CreateThread(0, 0, think, pcon, 0, &Id);
while(1)
{
  if (hThread == 0)
  break;
 if (!fgets(line, 256, stdin))
    continue;
 if (line[0] == '\n')
    continue;
 sscanf(line, "%s", command);
 if (!strcmp(command, "quit")) {
    pcon->fTimeout = TRUE;
return;
    }
}
... logic
... logic
}

---

Only after think thread is returned I need to perform the {... logic} part. Till then I need to loop and keep on checking if user inputs "quit". Suppose user inputs "quit" then fTimeout is set to "True" which will exit the thread. And also xboard() is returned to main().
But since I am entering the infinite while(1) loop before the thread is returned, I am not able to compare hThread to 0. So how to accomplish this please ?

For your previous errors, are you including windows.h somewhere before your prototype of think()? (Since things like WINAPI are needed...)

Also, what are you trying to do with that most recent while() loop? "since I am entering the infinite while(1) loop before the thread is returned" - then what is the point of the thread...? If you don't want the code to run concurrently, then why multithread? If you want to know if the thread is still running, there's a plethora of ways to do that... you can wait on a thread with the WaitFor*Object*() functions, or use GetExitCodeThread().

Another thing: if you use the C runtime at all, you should use __beginthreadex instead of CreateThread to start the new thread. It's defined in <process.h>.

Quote:

---

Another thing: if you use the C runtime at all, you should use __beginthreadex instead of CreateThread to start the new thread. It's defined in <process.h>.

---

Why? CreateThread is a Win32 API call, so that's what you are meant to use in Windows.

Because _beginthreadex does some extra initializing before calling CreateThread in turn, and also some cleanup before the thread finishes. If you use CreateThread directly, and then any CRT function that uses thread-local resources (quite a few of them), you leak resources for every thread that dies.

(I got the name wrong, though: it's only a single underscore in front.)

It's documented in msdn and I'm fairly sure it's also mentioned in either (or both) Petzold's 'Windows Programming' or Richter's 'Programming Applications for MS Windows'.

Quote:

---

Originally Posted by msdn,CreateThread

A thread in an executable that calls the C run-time library (CRT) should use the _beginthreadex and _endthreadex functions for thread management rather than CreateThread and ExitThread; this requires the use of the multi-threaded version of the CRT. If a thread created using CreateThread calls the CRT, the CRT may terminate the process in low-memory conditions.

---

Petzold uses _beginthread, which is fine for some uses, but provides fewer options. It is also paired with _endthread (which a thread created with _beginthread calls automatically upon ending!), which does not allow you to retrieve the thread exit code, because it closes the thread handle and, because _beginthread does not permit the creation of a sleeping thread, prevents the existence of a reliable way of duplicating it first. It's Richter who points out the problems and strongly recommends _beginthreadex over _beginthread.
Richter also has this to say about using CreateThread instead of _beginthreadex (paraphrased, translating back to English from my German version):

Quote:

---

Of course, a few problems remain. For example, the entire process is terminated if the thread calls the C/C++ runtime function signal, because the environment is not prepared for structured exception handling. In addition, if the thread ends without a call to _endthreadex, the data block [for the CRT thread-local data] cannot be freed, resulting in a memory leak. (And who would call _endthreadex for a thread created with CreateThread?)

---

Quote:

---

the data block [for the CRT thread-local data] cannot be freed

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If CreateThread threads would never free data, it would cause many many problems. I haven't seen these problems and that's why I don't believe this part.