Implement SharedMutex

[tshemsedinov]

• SharedMutex allow us to access shared resource in both ways exclusive and shared.
• Multiple threads can access resource for read access at a same time
• Only one threads can access resource for write access at a same time

class SharedMutex {
  status: SM_UNLOCKED | SM_READ_LOCK | SM_WRITE_LOCK,
  async enterRead(callback), // if no callback passed Promise will be returned
  async enterWrite(callback),
  leave(),
  on('status', (status => {})), // or you can subscribe on status change
}