与 MIDIPacketNext 崩溃

编程问答 2022-04-21

问题描述

十年前我用 PGMidi 用 Objective-C 编写了一个应用程序，它是 Core MIDI 的一个帮助类。 PGMidi 的输入函数如下所示：

static void PGMIDIReadProc(const MIDIPacketList *pktlist,void *readProcRefCon,void *srcConnRefCon) {
    PGMidiSource *source = arc_cast<PGMidiSource>(srcConnRefCon);
    [source midiRead:pktlist fromPort:source.name];
}

- (void) midiRead:(const MIDIPacketList *)pktlist fromPort:(NSString *)port {
    NSArray *delegates = self.delegates;
    for (NSValue *delegatePtr in delegates) {
        id<PGMidiSourceDelegate> delegate = (id<PGMidiSourceDelegate>)[delegatePtr pointerValue];
        [delegate midiSource:self midiReceived:pktlist fromPort:port];
    }
}

然后将数据传递给我的应用函数：

static NSMutableArray *packetToArray(const MIDIPacket *packet) {
    NSMutableArray *values = [[NSMutableArray alloc] initWithCapacity:3];
    NSNumber *value;
    for (int j=0; j<packet->length; j++) {
        value = [[NSNumber alloc] initWithUnsignedInt:packet->data[j]];
        [values addObject:value];
    }
    return values;
}

- (void)midiSource:(PGMidiSource *)midi midiReceived:(const MIDIPacketList *)packetList fromPort:(NSString *)port {
    const MIDIPacket *packet = &packetList->packet[0];
    for (int i=0; i<packetList->numPackets; ++i) {
        NSDictionary *data = [[NSDictionary alloc] initWithObjectsAndKeys:
            packetToArray(packet),@"values",port,@"port",nil];
        [self performSelectorOnMainThread:@selector(receiveMidiData:) withObject:data waitUntilDone:FALSE];
    
        packet = MIDIPacketNext(packet);
    }
}

这一直很好用。但今年早些时候，我将我的应用程序转换为 Swift。我单独离开了 PGMidi 类，但将我的应用程序功能重写为：

func packetToArray(_ packet: MIDIPacket) -> [Int] {
    var values = [Int]()
    let packetMirror = Mirror(reflecting: packet.data)
    let packetValues = packetMirror.children.map({ $0.value as? UInt8 })
    for i in 0..<Int(packet.length) {
        if (packetValues.count > i),let value = packetValues[i] {
            values.append(Int(value))
        }
    }
    return values
}

@objc func midiSource(_ midi: PGMidiSource,midiReceived packetList: UnsafePointer<MIDIPacketList>,fromPort port: String) {
    var packet = packetList.pointee.packet // this gets the first packet
    for _ in 0..<packetList.pointee.numPackets {
        let packetArray = App.packetToArray(packet)
        let data: [AnyHashable : Any] = [
            "values" : packetArray,"port" : port
        ]
        self.performSelector(onMainThread: #selector(receiveMidiData(_:)),with: data,waitUntilDone: false)

        packet = MIDIPacketNext(&packet).pointee
    }
}

这基本上有效，但我在 MIDIPacketNext 行上遇到了一些崩溃。这是不一致的，似乎在有大量数据输入时发生，例如来自键盘上的表情轮。一个崩溃日志包括：

Exception Type: EXC_BAD_ACCESS (SIGSEGV)
Exception Subtype: KERN_INVALID_ADDRESS at 0x000000016b78914c
VM Region Info: 0x16b78914c is not in any region. Bytes after previous region: 37197 Bytes before following region: 360050356
REGION TYPE START - END [ VSIZE] PRT/MAX SHRMOD REGION DETAIL
Stack 16b6f8000-16b780000 [ 544K] rw-/rwx SM=PRV thread 6
---> GAP OF 0x15768000 BYTES
unused shlib __TEXT 180ee8000-180f2c000 [ 272K] r-x/r-x SM=COW ... this process

另一个略有不同，但指向同一行代码：

Exception Type:  EXC_BAD_ACCESS (SIGBUS)
Exception Subtype: KERN_PROTECTION_FAILURE at 0x000000016beb46cc
VM Region Info: 0x16beb46cc is in 0x16beb4000-0x16beb8000;  bytes after start: 1740  bytes before end: 14643
      REGION TYPE                 START - END      [ VSIZE] PRT/MAX SHRMOD  REGION DETAIL
      Stack                    16be2c000-16beb4000 [  544K] rw-/rwx SM=PRV  thread 5
--->  STACK GUARD              16beb4000-16beb8000 [   16K] ---/rwx SM=NUL  ... for thread 9
      Stack                    16beb8000-16bf40000 [  544K] rw-/rwx SM=PRV  thread 9

我是否应该以不同方式访问数据包以避免这种情况，或者我可以做些什么来检测错误情况并避免崩溃？

解决方法

暂无找到可以解决该程序问题的有效方法，小编努力寻找整理中！

如果你已经找到好的解决方法，欢迎将解决方案带上本链接一起发送给小编。

小编邮箱:dio#foxmail.com (将#修改为@）

coremidiiosiosswiftswiftswift