[Fix CMAKE Configure Error] Detecting CXX compiler ABI info - failed

I use Cmake to generate code for OpenCV...
After finish configure..The it fail..

The direction of Cmake in E:\ Disk.

The CXX compiler identification is GNU 4.9.2
The C compiler identification is GNU 4.9.2
Check for working CXX compiler: C:/mingw64/mingw64/bin/x86_64-w64-mingw32-g++.exe
Check for working CXX compiler: C:/mingw64/mingw64/bin/x86_64-w64-mingw32-g++.exe -- works
Detecting CXX compiler ABI info
Detecting CXX compiler ABI info - failed
Detecting CXX compile features

Detecting CXX compile features - done


Detecting CXX compiler ABI info - failed????

So I have moved Cmake Folder to C:\ Folder.. And Done.

[ Fix QT Creator ] ASSERT: "!"No style available without QApplication!"" in file kernel\qapplication.cpp

Error (windows and ubuntu with last qt 5.7). I created qt quick 2 controls app, add chart 2d bar and try run project, but I've got an error.

File main.c 

#include <QGuiApplication>

#include <QQmlApplicationEngine>

int main(int argc, char *argv[])

{

    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);

    QGuiApplication app(argc, argv);

...
}

How to Fix it???

Easy to Fix... 

Maybe in this version,It doesn't support QGuiApplication.. 

So,you have to instead use QApplication..

1. Add widgets to file .pro to use QApplication

QT += quick widgets

2. in main.c change to use QApplication

#include <QApplication>
#include <QQmlApplicationEngine>

int main(int argc, char *argv[])
{
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
    QApplication app(argc,argv);
...
}

[ Linux Threading ] Thread - POSIX Libary

POSIX thread (pthread) libraries
The POSIX thread libraries are a standards based thread API for C/C++. It allows one to spawn a new concurrent process flow. It is most effective on multi-processor or multi-core systems where the process flow can be scheduled to run on another processor thus gaining speed through parallel or distributed processing. Threads require less overhead than "forking" or spawning a new process because the system does not initialize a new system virtual memory space and environment for the process. While most effective on a multiprocessor system, gains are also found on uniprocessor systems which exploit latency in I/O and other system functions which may halt process execution. (One thread may execute while another is waiting for I/O or some other system latency.) Parallel programming technologies such as MPI and PVM are used in a distributed computing environment while threads are limited to a single computer system. All threads within a process share the same address space. A thread is spawned by defining a function and its arguments which will be processed in the thread. The purpose of using the POSIX thread library in your software is to execute software faster.


Thread Basics:
Thread operations include thread creation, termination, synchronization (joins,blocking), scheduling, data management and process interaction.
A thread does not maintain a list of created threads, nor does it know the thread that created it.
All threads within a process share the same address space.
Threads in the same process share:

• Process instructions
• Most data
• open files (descriptors)
• signals and signal handlers
• current working directory
• User and group id

Each thread has a unique:

• Thread ID
• set of registers, stack pointer
• stack for local variables, return addresses
• signal mask
• priority
• Return value: errno

pthread functions return "0" if OK.


Thread Creation and Termination:

Example: pthread1.c
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>

void *print_message_function( void *ptr );

main()
{
     pthread_t thread1, thread2;
     const char *message1 = "Thread 1";
     const char *message2 = "Thread 2";
     int  iret1, iret2;

    /* Create independent threads each of which will execute function */

     iret1 = pthread_create( &thread1, NULL, print_message_function, (void*) message1);

     if(iret1)
     {
         fprintf(stderr,"Error - pthread_create() return code: %d\n",iret1);
         exit(EXIT_FAILURE);
     }

     iret2 = pthread_create( &thread2, NULL, print_message_function, (void*) message2);
     if(iret2)
     {
         fprintf(stderr,"Error - pthread_create() return code: %d\n",iret2);
         exit(EXIT_FAILURE);
     }

     printf("pthread_create() for thread 1 returns: %d\n",iret1);
     printf("pthread_create() for thread 2 returns: %d\n",iret2);

     /* Wait till threads are complete before main continues. Unless we  */
     /* wait we run the risk of executing an exit which will terminate   */
     /* the process and all threads before the threads have completed.   */

     pthread_join( thread1, NULL);

     pthread_join( thread2, NULL);

     exit(EXIT_SUCCESS);
}

void *print_message_function( void *ptr )
{
     char *message;
     message = (char *) ptr;
     printf("%s \n", message);
}

Compile:

C compiler: cc -pthread pthread1.c (or cc -lpthread pthread1.c)

or

C++ compiler: g++ -pthread pthread1.c (or g++ -lpthread pthread1.c)

The GNU compiler now has the command line option "-pthread" while older versions of the compiler specify the pthread library explicitly with "-lpthread".

Run: ./a.out

Results:

Thread 1

Thread 2

Thread 1 returns: 0

Thread 2 returns: 0

Details:

Thread Synchronization:

The threads library provides three synchronization mechanisms:

1.mutexes - Mutual exclusion lock: Block access to variables by other threads. This enforces exclusive access by a thread to a variable or set of variables.

joins - Make a thread wait till others are complete (terminated).

condition variables - data type pthread_cond_t

If register load and store operations for the incrementing of variable counter occurs with unfortunate timing (maybe call as interrupt or higher priority thread) , it is theoretically possible to have each thread increment and overwrite the same variable with the same value. Another possibility is that thread two would first increment counter locking out thread one until complete and then thread one would increment it to 2.

Mutexes:

Mutexes are used to prevent data inconsistencies due to operations by multiple threads upon the same memory area performed at the same time or to prevent race conditions where an order of operation upon the memory is expected. A contention or race condition often occurs when two or more threads need to perform operations on the same memory area, but the results of computations depends on the order in which these operations are performed. Mutexes are used for serializing shared resources such as memory. Anytime a global resource is accessed by more than one thread the resource should have a Mutex associated with it. One can apply a mutex to protect a segment of memory ("critical region") from other threads. Mutexes can be applied only to threads in a single process and do not work between processes as do semaphores.

Example threaded function:

#include <stdio.h>

#include <stdlib.h>

#include <pthread.h>

void *functionC();

pthread_mutex_t mutex1 = PTHREAD_MUTEX_INITIALIZER;

int  counter = 0;

main()

{

   int rc1, rc2;

   pthread_t thread1, thread2;

   /* Create independent threads each of which will execute functionC */

   if( (rc1=pthread_create( &thread1, NULL, &functionC, NULL)) )

   {

      printf("Thread creation failed: %d\n", rc1);

   }

   if( (rc2=pthread_create( &thread2, NULL, &functionC, NULL)) )

   {

      printf("Thread creation failed: %d\n", rc2);

   }

   /* Wait till threads are complete before main continues. Unless we  */

   /* wait we run the risk of executing an exit which will terminate   */

   /* the process and all threads before the threads have completed.   */

   pthread_join( thread1, NULL);

   pthread_join( thread2, NULL);

   exit(EXIT_SUCCESS);

}

void *functionC()

{

   pthread_mutex_lock( &mutex1 );

   counter++;

   printf("Counter value: %d\n",counter);

   pthread_mutex_unlock( &mutex1 );

}

Compile: cc -pthread mutex1.c (or cc -lpthread mutex1.c for older versions of the GNU compiler which explicitly reference the library)

Run: ./a.out

Results:

Counter value: 1

Counter value: 2

When a mutex lock is attempted against a mutex which is held by another thread, the thread is blocked until the mutex is unlocked. When a thread terminates, the mutex does not unless explicitly unlocked. Nothing happens by default.

Man Pages:

• pthread_mutex_lock() - acquire a lock on the specified mutex variable. If the mutex is already locked by another thread, this call will block the calling thread until the mutex is unlocked.
• pthread_mutex_unlock() - unlock a mutex variable. An error is returned if mutex is already unlocked or owned by another thread.
• pthread_mutex_trylock() - attempt to lock a mutex or will return error code if busy. Useful for preventing deadlock conditions.

2.Joins:

A join is performed when one wants to wait for a thread to finish. A thread calling routine may launch multiple threads then wait for them to finish to get the results. One waits for the completion of the threads with a join.

Sample code: join1.c

#include <stdio.h>

#include <pthread.h>

#define NTHREADS 10

void *thread_function(void *);

pthread_mutex_t mutex1 = PTHREAD_MUTEX_INITIALIZER;

int  counter = 0;

main()

{

   pthread_t thread_id[NTHREADS];

   int i, j;

   for(i=0; i < NTHREADS; i++)

   {

      pthread_create( &thread_id[i], NULL, thread_function, NULL );

   }

   for(j=0; j < NTHREADS; j++)

   {

      pthread_join( thread_id[j], NULL);

   }

   /* Now that all threads are complete I can print the final result.     */

   /* Without the join I could be printing a value before all the threads */

   /* have been completed.                                                */

   printf("Final counter value: %d\n", counter);

}

void *thread_function(void *dummyPtr)

{

   printf("Thread number %ld\n", pthread_self());

   pthread_mutex_lock( &mutex1 );

   counter++;

   pthread_mutex_unlock( &mutex1 );

}

Compile: g++ join.cpp -lpthread

Run: ./a.out

Results:

Thread number 1026

Thread number 2051

Thread number 3076

Thread number 4101

Thread number 5126

Thread number 6151

Thread number 7176

Thread number 8201

Thread number 9226

Thread number 10251

Final counter value: 10

[Fix QT] TLS initialization failed | QSslSocket::connectToHostEncrypted Fail

The solution of TLS initialization failed step by step:

1- Firstly you need to find your SSL version for your windows machine( SSL version strictly depends on QT versions) with this function:

#include <QCoreApplication>

#include <QDebug>

#include <QSslSocket> //To use QSslSocket Class

int main(int argc, char *argv[])

{

    QCoreApplication a(argc, argv);

    qDebug()<<QSslSocket::supportsSsl() << QSslSocket::sslLibraryBuildVersionString() << QSslSocket::sslLibraryVersionString();

    return a.exec();

}

Result: 

2- After that run your code and call the above function. It will print your required SSL version in application output. In my case, it was “OpenSSL 1.0.2p 14 Aug 2018” “” which may be different for all the users.

3- TLS initialization failed: Now Download the requires SSL libraries from the link given below:

https://indy.fulgan.com/SSL/Archive/

In my case: I download openssl-1.0.2p-x64_86-win64.zip

4- Paste all the files/content of SSL folder (which you have extracted) into the  debug folder. for eg: In my case it is:

E:\QT\NebProject\NASA_Vision\build-NASA_Vision-Desktop_Qt_5_12_2_MSVC2015_64bit-Debug\debug

Ok...Done