Playing a sound in a MIDI Callback function - c++

Question

I got this little piece of code which is working fine for now. However I want to play a sound in the callback function but I read in the MSDN pages:
"Applications should not call any multimedia functions from inside the callback function, as doing so can cause a deadlock. Other system functions can safely be called from the callback".
I'm quite new to programming and my question is: How can I work around this and still be able to play sounds when a MIDI-key is hit.
#include<iostream>
#include<cstdlib>
#include<windows.h>
#include<Mmsystem.h>
#include<stdio.h>
using namespace std;
void CALLBACK midiCallback(HMIDIIN handle, UINT uMsg, DWORD dwInstance, DWORD dwParam1, DWORD dwParam2)
{
switch (uMsg)
{
case MIM_OPEN:
cout << "-----OPENED.-----" << endl;
break;
case MIM_CLOSE:
cout << "-----EVERYTHING IS CLOSING.-----" << endl;
break;
case MIM_DATA:
cout << "-----APPARENTLY THERE I5 DATA.-----" << endl;
break;
case MIM_LONGDATA:
cout << "-----LONGDATA'D.-----" << endl;
break;
case MIM_ERROR:
cout << "-----ERROR.-----" << endl;
break;
case MIM_LONGERROR:
cout << "-----LONGERROR. EVEN WORSE.-----" << endl;
break;
}
cout << "dwInstance is " << dwInstance << endl;
cout << "Handle is " << handle << endl;
cout << "dwParam1 is " << dwParam1 << endl; //dwParam1 is the bytes of the MIDI Message packed into an unsigned long
cout << "dwParam1_hiword is " << HIWORD(dwParam1) << endl; //velocity
cout << "dwParam1_loword is " << LOWORD(dwParam1) << endl; //keyID
cout << "dwParam2 is " << dwParam2 << endl; //dwParam2 is the timestamp of key press
cout << "uMsg is " << uMsg << endl;
cout << "-----" << endl;
}
void MidiThing() {
MIDIINCAPS mic;
unsigned long result;
HMIDIIN inHandle;
unsigned long iNumDevs, i;
iNumDevs = midiInGetNumDevs(); /* Get the number of MIDI In devices in this computer */
/* Go through all of those devices, displaying their names */
for (i = 0; i < iNumDevs; i++)
{
/* Get info about the next device */
if (!midiInGetDevCaps(i, &mic, sizeof(MIDIINCAPS)))
{
/* Display its Device ID and name */
cout << "Device ID [" << i << "]: " << mic.szPname << endl;
}
}
cout << endl;
// Open the default MIDI In device. (DevID 0)
result = midiInOpen(&inHandle, 0, (DWORD)midiCallback, 0, CALLBACK_FUNCTION);
if (result != MMSYSERR_NOERROR) {
cout << "midiInOpen() failed...rv= " << result << endl;
}
else
{
midiInStart(inHandle);
}
cout << endl;
cout << "Press \"ESC\" to quit." << endl;
while (1) {
if (GetAsyncKeyState(VK_ESCAPE))
{
break;
cout << "exit=true." << endl;
}
Sleep(100);
}
midiInStop(inHandle);
midiInReset(inHandle);
midiInClose(inHandle);
cout << endl;
cout << inHandle << " was the MIDIIN handle." << endl;
cout << endl;
cout << "MIDI is closed now." << endl;
}
int main(int argc, char *argv[])
{
MidiThing();
cout << "Exit is success." << endl;
return EXIT_SUCCESS;
}

Answer 1

Wake up another thread from the callback.