CODEWITHSUNDEEP
c++multithreadingc++11
Wired365
Wired365

Reputation: 309

C++ Waiting for Multiple Threads

I can't seem to find an exact answer to the threading question I have. I currently have a program that polls the Kinect V2 sensor for new frame data using OpenNI2. The problem is I need to poll each type of sensor; depth, IR, and RGB separately in order to get them at the same time. Here is where my threading questions comes in, I want to poll each of the three sensors in their own individual thread and when all functions calls have returned continue with the data processing.

I understand how to link each new thread to the main thread to ensure all threads finish before the program exits, but how do I wait in the middle of my program for a specific set of threads to finish? Is there a function or feature of std::thread in c++11 that I am overlooking or is this something that needs to be manually done using a mutex or semaphores?

pseudocode:

std::thread thread_RGB(Kinect::readFrame(Enum::RGB), kinect_1);
std::thread thread_IR(Kinect::readFrame(Enum::IR), kinect_1);
std::thread thread_depth(Kinect::readFrame(Enum::depth), kinect_1);

// Wait for all threads to finish getting new frame data
...

// Process data here
process_data(kinect_1.RGB_data);
process_data(kinect_1.IR_data);
process_data(kinect_1.depth_data);

Upvotes: 4

Views: 6389

Answers (1)

Petar Velev
Petar Velev

Reputation: 2355

You need to call .join method to wait for the threads to finish and then destruct them. When you call t.join() there is a check if the thread is still doing something and if the work is done the thread is joined. If the thread is not joinable(there is also t.joinable()) the main thread will wait till the secondary thread finish its work and then join it.

In your case you can add these lines.

thread_RGB.join();
thread_IR.join();
thread_depth.join();

Here is an image I found on google that shows how thread::join() works.

Upvotes: 3

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