DLLCC and RtMidi (Real Time MIDI) Interface

-----Original Message-----
From: Wallen, David [mailto:[hidden email]]
Sent: 9 April 2013 7:45 a.m.
To: [hidden email]; [hidden email]
Subject: RE: [vwnc] DLLCC and RtMidi (Real Time MIDI) Interface

In addition to Steve’s notes, hopefully some of the following rambling will be of use. In no particular order…

I.

msg := 'Take me to the C'.

msgPointer := msg.

interface testChar: msg size with: msgPointer.

I think this works because DLLCC automatically appends the null terminator when passing a Smalltalk ByteString.

(If you pass a ByteArray instead, DLLCC has no inclination to append a null, and the C function will interpret all the ensuing chars up to the first zero byte valued character, wherever that occurs, as the intended string. This can cause all sorts of trouble.)

> msg := #[144 94 127] copy.

> msgPointer := msg.

>

> interface testChar: msg size with: msgPointer.

I don't think the above will include the null terminator, so it's good that you use the loop in this case. I'm a little surprised that the cout<< call works in the C function--perhaps the next char on the heap is a zero byte.

II.

> [if

> openOutputPort: 1;   “<<<fails here…”

> testOutput] ensure: [interface close]

I'm probably missing something, but here it looks like you're not passing the other required parameters to the call. I assume there's another Smalltalk method which fills in the missing parameters and makes the actuall DLLCC call using, say:

openOutPort: dev with: portNumber with: portName

Eg., you'd want something like:

   if openOutPort: 1 with: 115 with: 'abc'.

or

   if openOutPort: 1 with: 115 with: 'abc' copyToHeap.

(You can test this by inspecting:

                ('abc' copyToHeap) copyCStringFromHeap

Note that I wouldn't use gcCopy variants at first because they can involve garbage collection surprise issues. For example, if the DLL expects to use the pointer later, you don't want it to be GC'd. This can be tricky with thapi. Also, structs that contain gcMalloc'd objects do not (iirc) know enough to tell the GC to stay away from their member objects. So, a held reference to a struct will not prevent its internal gcMalloc'd members from disappearing. Later, replace malloc with gcMalloc and see what needs tweaking. (This development approach is okay as long as your development image can tolerate some buildup of un-freed pointers.)

III.

> msg := #[144 94 127] copy.

> msgPointer := msg gcCopyToHeap.

>

> interface sendMessage: outputDevice with: msg size with: msgPointer.

I’m not sure why this fails. In your C function, you appear to be successfully appending the characters to an empty Vector. Assuming that the receiver of the Vector object knows how to deal with it, things should work.

IV.

On a minor note, you might also want to check that the type, int64_t is declared to be a long long (assuming it's 64-bits).

Eg., here’s an example from MySQLInterface,

                my_ulonglong

                   <C: typedef unsigned long long my_ulonglong>

Hth,

-Dave

1) Failing Scenario….Smalltalk code…

testOutput

"

| if |

RtMidiExternalInterface unloadLibraries.

(if := self new)

open.

[if

openOutputPort: 1;   “<<<fails here…”

testOutput] ensure: [interface close]

“

| msg msgPointer |

RtMidiExternalInterface unloadLibraries.

msg := #[144 94 127] copy.

msgPointer := msg gcCopyToHeap.

External interface….

openOutPort: dev with: portNumber with: portName

<C: rtErr openOutPort(outDevice * dev, int64_t portNumber, char * portName)>

^self externalAccessFailedWith: _errorCode

C Code…

rtErr openOutPort( outDevice* dev, int64_t portNumber, char* portName ){

     try {

         std::cout << "openOutPort\n";

         //const char *s = "Hello, World!";   // works ok with these

         //std::string name(s); 

         std::string name(portName);    //<<<<<<  fails here

         std::cout << "Pre openPort\n";

         dev->ptr->openPort(portNumber, name);

         std::cout << "Pre RTMIDI_NOERROR\n";

         return RTMIDI_NOERROR;

     }

     catch ( RtError &error ) {

          error.printMessage();

          return RTMIDI_ERROR;

     }

};

Console output….

newMidiInDevice

getInPortCount

getInPortName

getInPortName

getInPortName

newMidiOutDevice

getOutPortCount

getOutPortName

getOutPortName

openOutPort

Error log…

8   libstdc++.6.dylib             0x95ff4b12 std::__throw_logic_error(char const*) + 121

9   libstdc++.6.dylib             0x9601edb5 char* std::string::_S_construct<char const*>(char const*, char const*, std::allocator<char> const&, std::forward_iterator_tag) + 163

10  libstdc++.6.dylib             0x9601ee76 std::basic_string<char, std::char_traits<char>, std::allocator<char> >::basic_string(char const*, std::allocator<char> const&) + 60

11  librtmidi.dylib               0x0a76e859 openOutPort + 121

12  com.cincom.vw7.9.1             0x00077da9 pdCallC + 2545 (unx86CallC.c:368)

13  com.cincom.vw7.9.1             0x00006a26 primCallVarArgC + 332 (exCallC.c:512)

14  com.cincom.vw7.9.1             0x0005ee2b rtPrimGlueVarArgMany + 43

2) This works fine…Smalltalk code…

testChar

| msg msgPointer |

"

100 timesRepeat: [self new testChar].

"

RtMidiExternalInterface unloadLibraries.

interface := RtMidiExternalInterface new.

msg := 'Take me to the C'.

msgPointer := msg.

interface testChar: msg size with: msgPointer.

msg := #[144 94 127] copy.

msgPointer := msg.

External interface….

testChar: messageLength with: message

<C: rtErr testChar(int  messageLength, char*  message)>

C Code…..

rtErr testChar(int messageLength, char* message ){

        std::cout << "testChar\n";

        std::cout << message;

        std::cout << "\nPre for loop\n";

        for (int i = 0; i < (int)messageLength; ++i)

            { std::cout << "Each:\n";

                printf("dec: %d char: %c\n", message[i], message[i]);

            }

        return RTMIDI_NOERROR;

};

Console output, all good…

testChar

Take me to the C

Pre for loop

Each:

dec: 84 char: T

Each:

dec: 97 char: a

Each:

dec: 107 char: k

Each:

dec: 101 char: e

Each:

dec: 32 char:  

Each:

dec: 109 char: m

Each:

dec: 101 char: e

Each:

dec: 32 char:  

Each:

dec: 116 char: t

Each:

dec: 111 char: o

Each:

dec: 32 char:  

Each:

dec: 116 char: t

Each:

dec: 104 char: h

Each:

dec: 101 char: e

Each:

dec: 32 char:  

Each:

dec: 67 char: C

testChar

?^

Pre for loop

Each:

dec: -112 char: ?

Each:

dec: 94 char: ^

Each:

dec: 127 char: 

rtErr openOutPort( outDevice* dev, int64_t portNumber, char* portName ){

     try {

          std::string name(portName); 

          dev->ptr->openPort(portNumber, name);

          return RTMIDI_NOERROR;

     }

     catch ( RtError &error ) {

          error.printMessage();

          return RTMIDI_ERROR;

     }

};

rtErr sendMessage( outDevice* dev, int64_t messageLength, uint8_t* message ){

     try {

          std::vector<uint8_t> msgVector;

          for (int i = 0; i < (int)messageLength; ++i)

          {

               msgVector.push_back(message[i]);

          }

          dev->ptr->sendMessage(&msgVector);

          return RTMIDI_NOERROR;

     }

     catch ( RtError &error ) {

          error.printMessage();

          return RTMIDI_ERROR;

     }

};

What is the correct way of passing in a ByteArray into this function?

Any help appreciated!

Thanks,

Stewart