Practical Sockets and Threads Derek Weitzel

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Practical Sockets and ThreadsDerek Weitzel
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Windows Threads

• Concurrent processing
• Windows Create Thread
• HANDLE WINAPI CreateThread( LPSECURITY_ATTRIBUTES
  lpThreadAttributes, SIZE_T dwStackSize,
  LPTHREAD_START_ROUTINE lpStartAddress, LPVOID
  lpParameter, DWORD dwCreationFlags, LPDWORD
  lpThreadId )
• Returns HANDLE to new thread, HANDLE is used in
  other functions to modify and control the thread
• Usually just pass 0 for lpThreadAttributes,
  dwStackSize, dwCreationFlags, lpThreadId -gt
  usually used the HANDLE

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Windows Threads

• HANDLE WINAPI CreateThread( LPSECURITY_ATTRIBUTES
  lpThreadAttributes, SIZE_T dwStackSize,
  LPTHREAD_START_ROUTINE lpStartAddress, LPVOID
  lpParameter, DWORD dwCreationFlags, LPDWORD
  lpThreadId )
• lpStartAddress is a void pointer to a function
  defined as DWORD WINAPI ThreadProc( LPVOID
  lpParameter )
• lpParameter is another void pointer to data that
  you want passed to the Thread Function

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POSIX Threads (pthreads)

• Same idea as Windows!
• int pthread_create(pthread_t thread, const
  pthread_attr_t attr, void (start_routine)(void
  ), void arg)
• Must create a pthread_t variable to hold the
  thread pointer, used further to control thread
• Thread attr can be 0, and I usually use 0
• Pointer to a function defined asvoid
  start_routine(void)
• arg is the void to the arguments

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Exiting Threads

• 2 ways
• Can exit normally, simply calling exit(int) or
  reach the end of the Thread Function
• Can call special thread functionsWindows VOID
  WINAPI ExitThread( DWORD dwExitCode )Pthreads
  void pthread_exit(void value_ptr)

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Force Stop Threads

• WindowsBOOL WINAPI TerminateThread( HANDLE
  hThread, DWORD dwExitCode )
• Where hThread is the HANDLE returned by the
  CreateThread function.
• Pthreads
• int pthread_cancel(pthread_t thread)

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Mutex

• Used to prevent race conditions with variables
• Windows
• HANDLE CreateMutex( LPSECURITY_ATTRIBUTES
  lpMutexAttributes, BOOL bInitialOwner, LPCTSTR
  lpName ) where lpMutexAttributes is always
  0bInitialOwner TRUE if caller wants ownership,
  otherwise falselpName char to the name of the
  mutex, used to distinguish the mutexreturn
  HANDLE to the Mutex

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Mutex

• Pthread
• int pthread_mutex_init( pthread_mutex_t mutex,
  const pthread_mutexattr_t attr)
• Where mutex is the variable to be used for the
  mutex
• Usually use 0 for attr

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Locking Mutex

• Windows
• The CreateMutex function automatically locks the
  mutex to the calling thread. The char

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Sockets

• Low-Level Network communication
• Most every program that communicates on the
  internet, uses Sockets, though usually abstracted
  through apis

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Windows Sockets

• Follows the Berkley Sockets model, with 1
  exception
• Must callint WSAStartup( WORD
  wVersionRequested, LPWSADATA lpWSAData )
• These paramaters are difficult to find, so I just
  use the codeWSADATA WsaDat
• WSAStartup(MAKEWORD(2,2), WsaDat)

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Berkley Sockets

• Create the socket
• Int socket(int socket_family, int socket_type,
  int protocol)
• Where socket_family is usually PF_INET(linux) or
  AF_INET(windows) socket_type can be
• SOCK_STREAM TCP
• SOCK_DGRAM - UDP
• Protocol is usually 0, but can be IPPROTO_TCP or
  IPPROTO_UDP in windows

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TCP vs DGRAM

• TCP
• Reliable information transfer
• Guaranteed to be in correct order and uncorrupted
• Guaranteed to be received by connected computer
• Unclear where messages begin and end, stream like
  operation
• UDP
• Not guaranteed that the information will reach
  connected computer
• Not guaranteed to be in order, though guaranteed
  to be un-corrupted
• Clear beginning and end

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Socket Functions

• Bind
• int bind( SOCKET s, const struct sockaddr name,
  int namelen )
• Binds to the specified ip (usually your own) and
  port
• Usually used for server side, to Listen for
  connections

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Socket Functions

• Listen
• int listen( SOCKET s, int backlog )
• Socket s specifies socket created by socket
  function
• Backlog is max length of queue of incoming
  connections
• Used to listen for incoming connections, accept
  connections with accept function

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Socket Functions

• Accept
• Used mostly on server side communication
• SOCKET accept( SOCKET s, struct sockaddr addr,
  int addrlen )
• Returns the connected socket
• SOCKET s is the listening socket
• Addr is the structure to hold the address
  information of the socket
• Addrlen is the sizeof addr

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Socket Functions

• Send
• Used to send information
• Send for TCP
• int send( SOCKET s, const char buf,int len, int
  flags )
• Buf is character array of length len
• Send for UDP
• int sendto( SOCKET s, const char buf, int len,
  int flags, const struct sockaddr to, int tolen
  )
• to is structure specifing the receiver of the
  packet

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Socket Functions

• Receive for TCP
• int recv( SOCKET s, char buf,int len, int flags
  )
• Returns amount of bytes read in (a char is a byte
  in length, normally)
• buf is a character array previously made of
  length len
• Flags can be left as 0

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Socket Functions

• Receive for UDP
• int recvfrom( SOCKET s, char buf, int len, int
  flags, struct sockaddr from, int fromlen )
• From is structure to hold the senders
  information of length fromlen

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Socket Functions

• Select
• Used to poll the condition of sockets, useful to
  see status of multiple of socket
• int select( int nfds, fd_set readfds, fd_set
  writefds, fd_set exceptfds, const struct
  timeval timeout )
• Nfds is largest value of the sockets (theyre
  ints)
• Fd_set provides macros, shown in examples

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Resources

• www.msdn.com Microsoft Developer Network
• http//www.yolinux.com/TUTORIALS/LinuxTutorialPosi
  xThreads.html - pthread tutorial