Wait to solve the zombie process

C0301—2022.0315
Process general statement
Call... In the parent process wait function , See the effect . The whole parent process does three things ： Print twice 、 One call wait function .

One 、 The subprocess makes an endless loop .

int pid = 0;
	int status = 0;// state 
	int res = 0;//wait Return value 
	pid = fork();
	if (pid == 0)
	{
    
		cout << " Enter the subprocess logic  pid=" << getpid() << endl;
		for (int i = 0; i >-1; i++)
		{
    
			cout << " Subprocesses  for i=" << i << endl;
			sleep(2);// Prevent printing too fast 
		}
	}
	else if (pid>0)
	{
    
		cout << " Enter the parent process logic  pid=" << getpid() << endl;
		res = wait(&status);
		cout << "wait after   The parent process "<< endl;
	}

because VS return Breaking points can't end , So use linux Kernel compilation runs .
Generate — Rebuild the solution

To Ubuntu Find the folder where the project is located , Right click Open at terminal

Compile run discovery
（1） The subprocess has been in an endless loop

（2） The parent process only takes the first step , And in a wakeable state of sleep .
wait Wait for the subprocess to finish before returning the value , The subprocess in this example is an endless loop .

Two 、 The subprocess loop can end , Observe the parent process call wait What happens after the function

	int pid = 0;
	int status = 0;// state 
	int res = 0;//wait Return value 
	pid = fork();
	if (pid == 0)
	{
    
		cout << " Enter the subprocess logic  pid=" << getpid() << endl;
		for (int i = 0; i <10; i++)
		{
    
			cout << " Subprocesses  for i=" << i << endl;
			sleep(2);
		}
	}
	else if (pid>0)
	{
    
		cout << " Enter the parent process logic  pid=" << getpid() << endl;
		res = wait(&status);
		cout << "wait after   The parent process  res="<<res<< endl;
	}

After compiling and running , In circulation

After the subprocess cycle ends , You can see , The parent process printed the call wait Statement after function . After the subprocess cycle ends ,wait Function returns the ID, Then print the following statement .

Thus we can see that ,wait The function blocks , After the subprocess runs , Then return to the child process ID, Then the following operations .

Can solve , The child process ends before the parent process , Problems causing the zombie process .