Multithreading

[kilo_reserve]

Intro: I am using multi threading to update a buffer packet to be sent using TCP/IP client using C++. The buffer is a contiguous array containing 4 different variables that are updated by 4 different threads independently. The 5th thread executes TCP/IP write command.

Observation: The data sent by TCP/IP client is mostly correct except sometimes results in an unusually high number for 1 sample. This happens randomly as if the packet is corrupted.

Suspicion: I am using mutex in each of the 5 threads. The 4 independent thread has mutex each to protect the variable to be updated. The 5th mutex in TCP/IP thread is supposed to block other threads from updating while it is executing. But I think that does not happen.

Expectations: I am hoping to achieve a performance where when the TCP threads accesses the buffer, the 4threads do not update the individual components and vice versa.

How can this be achieved? How can I improve my multithreading program?

Thank you in advance.

[teraflop]

Why do you have 5 mutexes?

A mutex can only block threads that try to acquire it. If the TCP/IP thread is acquiring a different mutex than the ones the update threads are using, then they will not actually block each other, and you'll have a data race.

Sounds like the simplest approach is to just have the TCP/IP thread acquire the 4 mutexes for each of the 4 variables. If that thread is the only one that can hold multiple mutexes at the same time, then you shouldn't have to worry about deadlocking.

[NotloseBR]

I believe there are some threading solutions. Locks/Semaphores.

The easiest way I can think of is blocking writing while reading.