The following example runs hcidump on a child thread.  This happens to be a bluetooth bluez tool which continuously outputs events as it seens them. This code allows this to happen on a child thread with the output passed back to the main application thread using a named pipe.

Create the pipe and the child thread process

#include <iostream>
#include <fcntl.h>
#include <unistd.h>

int our_input_fifo_filestream = -1;

	//--------------------------------------
	//----- CREATE A FIFO / NAMED PIPE -----
	//--------------------------------------
	int result;

	printf("Making FIFO...\n");
	result = mkfifo(OUR_INPUT_FIFO_NAME, 0777);		//(This will fail if the fifo already exists in the system from the app previously running, this is fine)
	if (result == 0)
	{
		//FIFO CREATED
		printf("New FIFO created: %s\n", OUR_INPUT_FIFO_NAME);
	}

	printf("Process %d opening FIFO %s\n", getpid(), OUR_INPUT_FIFO_NAME);
	our_input_fifo_filestream = open(OUR_INPUT_FIFO_NAME, (O_RDONLY | O_NONBLOCK));
					//Possible flags:
					//	O_RDONLY - Open for reading only.
					//	O_WRONLY - Open for writing only.
					//	O_NDELAY / O_NONBLOCK (same function) - Enables nonblocking mode. When set read requests on the file can return immediately with a failure status
					//											if there is no input immediately available (instead of blocking). Likewise, write requests can also return
					//											immediately with a failure status if the output can't be written immediately.
	if (our_input_fifo_filestream != -1)
		printf("Opened input FIFO: %i\n", our_input_fifo_filestream);


	//----------------------------------------------
	//----- RUN HCIDUMP ON A BACKGROUND THREAD -----
	//----------------------------------------------
	int pid2 = fork();
	if(pid2 == 0)
	{
		//----- THIS IS THE CHILD THREAD -----
		//cout << "I am the child" << endl;

		FILE* pipe2 = popen("sudo hcidump", "r");		//Send the command, popen exits immediately 
		if (pipe2)
		{
			//----- THIS CHILD THREAD WILL RUN FOREVER -----
			cout << "Bluetooth hcidump child thread started" << endl;

			//Create an output filestream for this child thread
			int our_output_fifo_filestream = -1;
			our_output_fifo_filestream = open(OUR_INPUT_FIFO_NAME, (O_WRONLY | O_NONBLOCK));
								//Possible flags:
								//	O_RDONLY - Open for reading only.
								//	O_WRONLY - Open for writing only.
								//	O_NDELAY / O_NONBLOCK (same function) - Enables nonblocking mode. When set read requests on the file can return immediately with a failure status
								//											if there is no input immediately available (instead of blocking). Likewise, write requests can also return
								//											immediately with a failure status if the output can't be written immediately.
			if (our_output_fifo_filestream != -1)
				cout << "Opened output FIFO: " << our_output_fifo_filestream << endl;

			char buffer2[128];
			while(!feof(pipe2))						//Wait for the output resulting from the command
			{
				if(fgets(buffer2, 128, pipe2) != NULL)
				{
					write(our_output_fifo_filestream, (void*)buffer2, strlen(buffer2));	
					//cout << buffer2 << endl;
				}
			}
			cout << "Bluetooth hcidump child thread ending" << endl;
			pclose(pipe2);
		}
		_exit(0);		//Don't forget to exit!
	}
	else
	{
		//cout << "I am the parent\n" << endl;
		wait();		//Optional if you want to wait on the child thread, remove if not
	}

Reading the output from the main application thread

	//---------------------------------------------
	//----- CHECK FIFO FOR ANY RECEIVED BYTES -----
	//---------------------------------------------
	// Read up to 255 characters from the port if they are there
	if (our_input_fifo_filestream != -1)
	{
		unsigned char buffer3[256];
		int length3 = read(our_input_fifo_filestream, (void*)buffer3, 255);		//Filestream, buffer to store in, number of bytes to read (max)
		if (length3 < 0)
		{
			//An error occured (this can happen)
		}
		else if (length3 == 0)
		{
			//No data waiting
		}
		else
		{
			//Bytes received
			buffer3[length3] = '\0';
			cout << buffer3 << endl;
		}
	}
USEFUL?
We benefit hugely from resources on the web so we decided we should try and give back some of our knowledge and resources to the community by opening up many of our company’s internal notes and libraries through mini sites like this. We hope you find the site helpful.
Please feel free to comment if you can add help to this page or point out issues and solutions you have found, but please note that we do not provide support on this site. If you need help with a problem please use one of the many online forums.

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