Transcript acm powerpoint

Practical Sockets and
Threads
Derek Weitzel
Windows Threads
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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 -> usually used the
HANDLE
Windows Threads
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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
POSIX Threads (pthreads)
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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 as:
void* start_routine(void*)
• arg is the void* to the arguments
Exiting Threads
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2 ways:
• Can exit normally, simply calling exit(int) or
reach the end of the Thread Function
• Can call special thread functions:
Windows: VOID WINAPI ExitThread( DWORD
dwExitCode );
Pthreads: void pthread_exit(void *value_ptr);
Force Stop Threads
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Windows:
BOOL WINAPI TerminateThread( HANDLE
hThread, DWORD dwExitCode );
• Where hThread is the HANDLE returned by the
CreateThread function.
Pthreads:
• int pthread_cancel(pthread_t thread);
Mutex
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Used to prevent race conditions with variables
Windows:
• HANDLE CreateMutex(
LPSECURITY_ATTRIBUTES lpMutexAttributes,
BOOL bInitialOwner, LPCTSTR lpName );
where lpMutexAttributes is always 0
bInitialOwner: TRUE if caller wants ownership,
otherwise false
lpName: char* to the name of the mutex, used
to distinguish the mutex
return: HANDLE to the Mutex
Mutex
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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
Locking Mutex
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Windows:
• The CreateMutex function automatically locks
the mutex to the calling thread. The char*
Sockets
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Low-Level Network communication
Most every program that communicates on the
internet, uses Sockets, though usually abstracted
through api’s
Windows Sockets
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Follows the Berkley Sockets model, with 1
exception
• Must call:
int WSAStartup(
WORD wVersionRequested,
LPWSADATA lpWSAData );
• These paramaters are difficult to find, so I just
use the code:
WSADATA WsaDat;
WSAStartup(MAKEWORD(2,2), &WsaDat);
Berkley Sockets
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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:
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SOCK_STREAM – TCP
SOCK_DGRAM - UDP
• Protocol is usually 0, but can be IPPROTO_TCP
or IPPROTO_UDP in windows
TCP vs DGRAM
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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
Socket Functions
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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
Socket Functions
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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
Socket Functions
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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
Socket Functions
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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
Socket Functions
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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
Socket Functions
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Receive for UDP
• int recvfrom( SOCKET s, char* buf, int len,
int flags, struct sockaddr* from,
int* fromlen );
• From is structure to hold the sender’s
information of length fromlen
Socket Functions
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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 (they’re
ints)
• Fd_set provides macros, shown in examples
Resources
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www.msdn.com – Microsoft
Developer Network
http://www.yolinux.com/TUTORIALS/
LinuxTutorialPosixThreads.html pthread tutorial