Hello i need a hand on spawning a thread properly, i cant seem to get the syntax correct.
here is my code ...
// Spawn a thread--------------------------------------------------#
pthread_t thread1; // thread object
int rc1;
if( (rc1=pthread_create( &thread1, NULL, spellCheck, NULL)) )
{
cout << "Thread creation failed: " << rc1 << endl;
}
pthread_join( thread1, NULL);
function definition
void spellCheck(vector<string> * fileRead, list<string> * incorrectWord, vector<string> * correctWord)
{
header file
void spellCheck(vector<string> *fileRead, list<string> *incorrectWord, vector<string> *correctWord);
Any help would be much appreciated :)
my error:
server.cpp:142: error: invalid conversion from 'void ()(std::vector<std:................. initializing argument 3 of 'int pthread_create(pthread_t, const pthread_attr_t*, void* ()(void), void*)'
I may be wrong here but I thought that the thread function you implement and pass to pthread_create() could only have a single (void*) input argument
Related
I apologize in advance for my English :D
How can I call a function from a process, knowing the pointer to it?
I tried this:
Process.cpp:
DWORD pid;
HWND hwnd;
HANDLE phandle;
void Attach() {
hwnd = FindWindow(NULL, L"GTA:SA:MP");
if (!hwnd) {
cout << "Process is not found" << endl;
system("pause");
}
else if (hwnd) {
cout << "Process was successfully loaded" << endl;
GetWindowThreadProcessId(hwnd, &pid);
phandle = OpenProcess(PROCESS_VM_READ, 0, pid);
}
else
{
cout << "Error 0x01" << endl;
system("pause");
}
}
void GameText(const char* szText, int iTime, signed int iStyle)
{
typedef void(__stdcall* GameText_t)(const char*, int, signed int);
GameText_t pGameText = (GameText_t)((char*)phandle + 0x69F2B0);
return pGameText(szText, iTime, iStyle);
}
main.cpp:
int main()
{
std::cout << "Hello World!\n";
Attach();
GameText("~r~Test!", 1000, 5);
}
And I get the following exception:
An exception was thrown at the address 0x006EF7B6 in wh_mta.exe:
0xC0000005: access violation during execution at 0x006EF7B6.
Why is this happening? How can I call a function by its pointer through HANDLE?
P.S
Reading an integer through HANDLE works great.
int Read_Int(int address) {
int value;
ReadProcessMemory(phandle, (void*)address, &value, sizeof(value), 0);
return value;
}
Maybe 30 years ago that would have worked :D :D :D
Processes can't access each other's memory… Every process has their own image of the memory, so address 0xWHATEVER in a process does not contain the same data as 0xWHATEVER in another process!
You need to make a library or use some inter process communication (IPC).
What you are doing is adding the pointer to the HANDLE of the process. You need the address of the process in it's virtual address space. To do so, use EnumProcessModules andGetModuleFileNameEx to find the filename of the module with the function you want. (Could be an EXE or a DLL.) EnumProcessModules returns an array of HMODULES which are just addresses of module in the specified process's virtual address space. So loop through the array, then cast the HMODULE that you need to a PBYTE. Then, add the function pointer to it, then try to execute.
Also, according your code, you are going to execute the function in YOUR program. That's fine, just make sure that if it needs to run in the target program, you'll need to use CreateRemoteThread to run it there.
I have thread creation problem using Pthread. My code is as follows. I show only some portion due to space constraints.
Main.c create Detectdirection instance and send to the function.
d = new Detectdirection();
while(run)
{
int ret = d->run_parallel(d);
if(ret == -1)
run = false;
}
My Detectdirection Class has two functions to run in parallel:
class Detectdirection{
public:
int run_parallel(void*p);
void *Tracking(void *p);
static void *Tracking_helper(void * p);
void *ReadImage(void *p );
static void *ReadImage_helper(void *p );
private:
pthread_t thread[2];
}
void *Detectdirection::ReadImage(void *p){
Detectdirection *app = (Detectdirection*)p;
while(run){
}
pthread_exit(NULL);
}
void *Detectdirection::Tracking(void *p){
Detectdirection *app = (Detectdirection*)p;
while(run){
}
pthread_exit(NULL);
}
void *Detectdirection::Tracking_helper(void *p){
Detectdirection *app = (Detectdirection*)p;
return ((Detectdirection*)p)->Tracking(app);
}
void *Detectdirection::ReadImage_helper(void *p ){
Detectdirection *app = (Detectdirection*)p;
return ((Detectdirection*)p)->ReadImage(app);
}
int Detectdirection::run_parallel(void* p){
Detectdirection *app = (Detectdirection*)p;
int rc = pthread_create(&thread[0], NULL, app->ReadImage_helper, app);
if (rc) {
printf("ERROR; return code from pthread_create() is %d\n", rc);
return -1;
}
rc = pthread_create(&thread[1], NULL, app->Tracking_helper, app);
if (rc) {
printf("ERROR; return code from pthread_create() is %d\n", rc);
return -1;
}
return 0;
}
Compile is ok and when I run, I have thread creation error. That sort of return type 11 happens only when many threads are created. But now I create only two thread and I have that error. What could be wrong?
I believe your are getting EAGAIN (based on the error code 11). That (obivously) means your system doesn't have enough resources to create threads anymore.
POSIX documentation says:
[EAGAIN] The system lacked the necessary resources to create another
thread, or the system-imposed limit on the total number of threads in
a process {PTHREAD_THREADS_MAX} would be exceeded.
I am not quite sure the following is true.
But now I create only two thread and I have that error. What could be wrong?
Here,
while(run)
{
int ret = d->run_parallel(d);
if(ret == -1)
run = false;
}
You are creating in a loop and each call d->run_parallel() creates two threads. So, you are potentially creating infinite number of threads
as the loop only breaks when pthread_create() fails. So, you may want to look at this loop carefully whether you really want to do as it is right now.
You don't seem to join with the threads you create. So, you could detach the threads so that thread-specific resources are released immediately when the thread(s) exit.
You can do:
pthread_detach(pthread_self());
in both ReadImage_helper() and Tracking_helper() functions to detach them. This could potentially solve your resource issue.
If it's still present then you have to look at ways to limit the number of threads that are simultaneously running on your system. One possible option is to use thread pools -- create a fixed number of threads and assign them new tasks as the threads complete their current task(s).
Can somebody please explain to me why this simple code leaks memory?
I believe that since pthreads are created with detached state their resources should be released inmediatly after it's termination, but it's not the case.
My environment is Qt5.2.
#include <QCoreApplication>
#include <windows.h>
void *threadFunc( void *arg )
{
printf("#");
pthread_exit(NULL);
}
int main()
{
pthread_t thread;
pthread_attr_t attr;
while(1)
{
printf("\nStarting threads...\n");
for(int idx=0;idx<100;idx++)
{
pthread_attr_init(&attr);
pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
pthread_create( &thread, &attr, &threadFunc, NULL);
pthread_attr_destroy ( &attr );
}
printf("\nSleeping 10 seconds...\n");
Sleep(10000);
}
}
UPDATE:
I discovered that if I add a slight delay of 5 milliseconds inside the for loop the leak is WAY slower:
for(int idx=0;idx<100;idx++)
{
pthread_attr_init(&attr);
pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
pthread_create( &thread, &attr, &threadFunc, NULL);
pthread_attr_destroy ( &attr );
Sleep(5); /// <--- 5 MILLISECONDS DELAY ///
}
This is freaking me out, could somebody please tell me what is happening? How this slight delay may produce such a significant change? (or alter the behavior in any way)
Any advice would be greatly appreciated.
Thanks.
UPDATE2:
This leak was observed on Windows platforms (W7 and XP), no leak was observed on Linux platforms (thank you #MichaelGoren)
I checked the program with slight modifications on windows using cygwin, and memory consumption was steady. So it must be a qt issue; the pthread library on cygwin works fine without leaking.
#include <pthread.h>
#include <stdio.h>
#include <unistd.h>
void *threadFunc( void *arg )
{
printf("#");
pthread_exit(NULL);
}
int main()
{
pthread_t thread;
pthread_attr_t attr;
int idx;
while(1)
{
printf("\nStarting threads...\n");
for(idx=0;idx<100;idx++)
{
pthread_attr_init(&attr);
pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
pthread_create( &thread, &attr, &threadFunc, NULL);
pthread_attr_destroy ( &attr );
}
printf("\nSleeping 10 seconds...\n");
//Sleep(10000);
sleep(10);
}
}
Compiler optimizations or the OS it self can decide to do loop unrolling. That is your for loop has a constant bound (100 here). Since there is no explicit synchronization to prevent it, a newly created, detached thread can die and have its thread ID reassigned to another new thread before its creator returns from pthread_create() due to this unrolling. The next iteration is already started before the thread was actually destroyed.
This also explains why your added slight delay has less issues; one iteration takes longer and hence the thread functions can actually finish in more cases and hence the threads are actually terminated most of the time.
A possible fix would be to disable compiler optimizations, or add synchronization; that is, you check whether the thread still exist, at the end of the code, if it does you'll have to wait for the function to finish.
A more tricky way would be to use mutexes; you let the thread claim a resource at creation and by definition of PTHREAD_CREATE_DETACHED this resource is automatically released when the thread is exited, hence you can use try_lock to test whether the thread is actually finished. Note that I haven't tested this approach so I'm not actually sure whether PTHREAD_CREATE_DETACHED actually is working according to its definition...
Concept:
pthread_mutex_t mutex;
void *threadFunc( void *arg )
{
printf("#");
pthread_mutex_lock(&mutex);
pthread_exit(NULL);
}
for(int idx=0;idx<100;idx++)
{
pthread_attr_init(&attr);
pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
pthread_create( &thread, &attr, &threadFunc, NULL);
pthread_attr_destroy ( &attr );
pthread_mutex_lock(&mutex); //will block untill "destroy" has released the mutex
pthread_mutex_unlock(&mutex);
}
The delay can induce a large change in behavior because it gives the thread time to exit! Of course how your pthread library is implemented is also a factor here. I suspect it is using a 'free list' optimization.
If you create 1000 threads all at once, then the library allocates memory for them all before any significant number of those threads can exit.
If as in your second code sample you let the previous thread run and probably exit before you start a new thread, then your thread library can reuse that thread's allocated memory or data structures which it now knows are no longer needed and it is now probably holding in a free list just in case someone creates a thread again and it can efficiently recycle the memory.
It has nothing to do with compiler optimisations. Code is fine. Problem could be
a) Windows itself.
b) Qt implementation of pthread_create() with detached attributes
Checking for (a): Try to create many fast detached threads using Windows _beginthreadex directly and see if you get the same picture. Note: CloseHandle(thread_handle) as soon as _beginthreaex returns to make it detached.
Checking for (b): Trace which function Qt uses to create threads. If it is _beginthread then there is your answer. If it is _beginthreadex, then Qt is doing the right thing and you need to check if Qt closes the thread handle handle immediately. If it does not then that is the cause.
cheers
UPDATE 2
Qt5.2.0 does not provide pthreads API and is unlikely responsible for the observed leak.
I wrapped native windows api to see how the code runs without pthread library. You can include this fragment right after includes:
#include <process.h>
#define PTHREAD_CREATE_JOINABLE 0
#define PTHREAD_CREATE_DETACHED 1
typedef struct { int detachstate; } pthread_attr_t;
typedef HANDLE pthread_t;
_declspec(noreturn) void pthread_exit(void *retval)
{
static_assert(sizeof(unsigned) == sizeof(void*), "Modify code");
_endthreadex((unsigned)retval);
}
int pthread_attr_setdetachstate(pthread_attr_t *attr, int detachstate)
{
attr->detachstate = detachstate;
return 0;
}
int pthread_attr_init(pthread_attr_t *attr)
{
attr->detachstate = PTHREAD_CREATE_JOINABLE;
return 0;
}
int pthread_attr_destroy(pthread_attr_t *attr)
{
(void)attr;
return 0;
}
typedef struct {
void *(*start_routine)(void *arg);
void *arg;
} winapi_caller_args;
unsigned __stdcall winapi_caller(void *arglist)
{
winapi_caller_args *list = (winapi_caller_args *)arglist;
void *(*start_routine)(void *arg) = list->start_routine;
void *arg = list->arg;
free(list);
static_assert(sizeof(unsigned) == sizeof(void*), "Modify code");
return (unsigned)start_routine(arg);
}
int pthread_create( pthread_t *thread, pthread_attr_t *attr,
void *(*start_routine)(void *), void *arg)
{
winapi_caller_args *list;
list = (winapi_caller_args *)malloc(sizeof *list);
if (list == NULL)
return EAGAIN;
list->start_routine = start_routine;
list->arg = arg;
*thread = (HANDLE)_beginthreadex(NULL, 0, winapi_caller, list, 0, NULL);
if (*thread == 0) {
free(list);
return errno;
}
if (attr->detachstate == PTHREAD_CREATE_DETACHED)
CloseHandle(*thread);
return 0;
}
With Sleep() line commented out it works OK without leaks. Run time = 1hr approx.
If the code with Sleep line commented out is calling Pthreads-win32 2.9.1 library (prebuilt for MSVC) then the program stops spawning new threads and stops responding after 5..10 minutes.
Test environment: XP Home, MSVC 2010 Expresss, Qt5.2.0 qmake etc.
You forgot to join your thread (even if they are finished already).
Correct code should be:
pthread_t arr[100];
for(int idx=0;idx<100;idx++)
{
pthread_attr_init(&attr);
pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
pthread_create( &arr[idx], &attr, &threadFunc, NULL);
pthread_attr_destroy ( &attr );
}
Sleep(2000);
for(int idx=0;idx<100;idx++)
{
pthread_join(arr[idx]);
}
Note from man page:
Failure to join with a thread that is joinable (i.e., one that is not detached), produces a "zombie thread". Avoid doing this, since each zombie thread consumes some system resources, and when enough zombie threads have
accumulated, it will no longer be possible to create new threads (or processes).
How do I send in a std::string into my thread?
This is my code:
void* sendReminder(void*)
{
system("echo 'hello' >> buffer.txt");
}
int main()
{
string str1 = "somevalue";
pthread_t t1;
pthread_create(&t1, NULL, &sendReminder, NULL);
}
Use the fourth argument to pthread_create to send an "argument" to your function, just be sure to make a copy of it on the heap:
string *userData = new string("somevalue");
pthread_create(&t1, NULL, &sendReminder, (void *) userData);
If you'll be using pthread_join to wait on the new thread(s), suspending execution of the caller, you can get away with just passing an address of the local variable:
if (pthread_create(&t1, NULL, &sendReminder, (void *) &str1) == 0)
{
pthread_join(t1, &result);
// ...
You can retrieve the value with:
void* sendReminder(void* data)
{
std::string* userData = reinterpret_cast<std::string*>(data);
// Think about wrapping `userData` within a smart pointer.
cout << *userData << endl;
}
You pass the value in as a void* in the last argument to pthread_create. Inside the thread function, you cast the void* back to the type of the object that you passed in. In this case a string.
I was just wondering if it is possible (and if so, how) to get the return value of a thread in C++ (Windows). I have several threads, and I use WaitForMultipleObjects(...) on them. This waits until a thread is done, and returns the index of said thread, and all is well. However, I want to be able to obtain the return value of the thread that finished using its handle.
For example:
DWORD WINAPI Thread1(void *parameter){
...
if(...) return 0;
else return -1;
}
DWORD WINAPI Thread2(void *parameter){
...
if(...) return 1;
else return 0;
}
int main(){
HANDLE t1 = CreateThread(0, 0, Thread1, NULL, 0, 0);
HANDLE t2 = CreateThread(0, 0, Thread2, NULL, 0, 0);
HANDLE *threads = new HANDLE[2];
threads[0] = t1;
threads[1] = t2;
int result = WaitForMultipleObjects(2, threads, false, INFINITE);
if(result == 0){
//get the threads value here:
int retVal = SomeFunction(t1); //What is SomeFunction?
}
...
}
I have tried to use GetExitCodeThread(thread) but I'm assuming this returns a system exit code, as it always gives me a very strange integer. Does anyone know a way, or a workaround?
GetExitCodeThread is the correct function. Here is the MSDN description of what it does:
This function returns immediately. If the specified thread has not
terminated and the function succeeds, the status returned is
STILL_ACTIVE. If the thread has terminated and the function succeeds,
the status returned is one of the following values:
The exit value specified in the ExitThread or TerminateThread function.
The return value from the thread function.
The exit value of the thread's process.
The problem with most programmer is that they don't pay attention to compiler warnings. At level 4 (/W4), the compiler produces following warning when returning -1 from a function that is returning DWORD:
warning C4245: 'return' : conversion from 'int' to 'DWORD', signed/unsigned mismatch
you need to check for STILL_ACTIVE for the values one of these threads may still be active
You can use C++ 11's threads concepts using std::future.
See an example below.
int ReturnFrmThread() {
return 100;
}
int main() {
std::future<int> GetRetVal= std::async(ReturnFrmThread); // Execution of ReturnFrmThread starts
int answer = GetAnAnswer.get(); // gets value as 100;
// Waits until ReturnFrmThread has finished
}