bitmap - How can I lock my object using C# in dll -

i have i/p camera , function repeating , receiving each frame.

public bitmap processframe(bitmap frame) {  }  

here buffering place buffering last 100 bitmaps:

lock (writer) {    bm[now] = new bitmap(frame);    = (now == 99) ? 0 : + 1; } 

when press record record video, need save every buffered bitmaps , after have save incoming bitmaps received after pressing record. when press record , using code below save buffered bitmaps video file lose of incoming frames. incoming frames while processing section, dropped , don't want drop them.

lock (writer) {    (int = now; < 150; i++)    {       if (bm[i] == null)         break;       writer.writevideoframe(bm[i]);//adding frame existing open file    }    if (now != 0)    {       (int = 0; < - 1; i++)       {          writer.writevideoframe(bm[i]);//adding frame existing open file       }    } } 

here part incoming frames saved in video file

 lock (writer)  {     writer.writevideoframe(frame);//adding frame existing open file  } 

i have searched , found lock me. when saving buffered bitmaps lock lock writer bitmap has come stop @ writer , wait unlocked, did not help.

what should do? how can make safe thread? using opensource ispy , think make thread each frame , call thread. me save incoming frame.

instead of using silly fixed array type solution, why not use concurrentqueue? won't have deal threading since that's thread safe class. have 1 thread pulling frames head of queue , writing them , have other thread add.