Runtime issues on ARM but runs fine on x86 - c++

Question

I recently created an application that I developed on my x86 Linux machine. Basically it's just two threads that communicate over a pipe() with each other. Thread 0 listens on the read end and Thread 1 writes into that pipe. That program worked perfectly fine.
But when I copied the sources over to a RaspberryPi and built it, there were some runtime issues (but compiled with no errors). It seems that thread0 never gets something out of the pipe, it just blocks.
Since pipes are made for Interprocess communication, i thought it would also be thread safe (since there also are two different file descriptors for read and write end).
BUT: Stepping through the program in the Qt Creator debugger on the RPi, everything seemed to work fine! I know the debugger initializing certain variables different can lead to such conditions, but I couldn't find any usages of uninitialized variables etc. in my Code.
thread 1:
void *midiThread(void *fds)
{
midiDevice = ((int*)fds)[0]; // device file for midi input
midiBuffer = ((int*)fds)[1]; // write end of the pipe
unsigned char rawBuffer[MIDI_MSG_LENGTH];
while (read(midiDevice, rawBuffer, MIDI_MSG_LENGTH)
>= MIDI_MSG_LENGTH)
{
struct midievent_t currentEvent;
unsigned char *rawBuffer = (unsigned char *)buffer;
currentEvent.channel = rawBuffer[0] & 0x0f;
// ....
write(midiBuffer, &currentEvent, sizeof(struct midievent_t));
}
close(midiBuffer);
return NULL;
}
main thread:
void MidiInput::createMidiThread()
{
if (pipe(_midiBufferPipe) < 0)
{
// error
}
int fds[2];
fds[0] = _midiFileDescriptor;
fds[1] = _midiBufferPipe[1];
pthread_create(&_midiThreadId, NULL,
midiThread, fds);
}
bool MidiInput::read(midievent_t *event)
{
if (!_initialized)
{
return false;
}
if (read(_midiBufferPipe[0], event, sizeof(struct midievent_t))
< sizeof(struct midievent_t))
{
// some error
return _initialized = false;
}
return true;
}