connect(2) connect(2) opendir/readdir(3) opendir/readdir(3) connect − initiate a connection on a socket

connect(2) connect(2) opendir/readdir(3) opendir/readdir(3) connect − initiate a connection on a socket
connect(2)
connect(2)
NAME
opendir/readdir(3)
opendir/readdir(3)
NAME
connect − initiate a connection on a socket
opendir − open a directory / readdir − read a directory
SYNOPSIS
SYNOPSIS
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <dirent.h>
int connect(int sockfd, const struct sockaddr *serv_addr, socklen_t addrlen);
DIR *opendir(const char *name);
DESCRIPTION
The file descriptor sockfd must refer to a socket. If the socket is of type SOCK_DGRAM then the
serv_addr address is the address to which datagrams are sent by default, and the only address from which
datagrams are received. If the socket is of type SOCK_STREAM or SOCK_SEQPACKET, this call
attempts to make a connection to another socket. The other socket is specified by serv_addr, which is an
address (of length addrlen) in the communications space of the socket. Each communications space interprets the serv_addr parameter in its own way.
Generally, connection-based protocol sockets may successfully connect only once; connectionless protocol
sockets may use connect multiple times to change their association. Connectionless sockets may dissolve
the association by connecting to an address with the sa_family member of sockaddr set to AF_UNSPEC.
RETURN VALUE
struct dirent *readdir(DIR *dir);
int readdir_r(DIR *dirp, struct dirent *entry, struct dirent **result);
DESCRIPTION opendir
The opendir() function opens a directory stream corresponding to the directory name, and returns a pointer
to the directory stream. The stream is positioned at the first entry in the directory.
RETURN VALUE
The opendir() function returns a pointer to the directory stream or NULL if an error occurred.
DESCRIPTION readdir
If the connection or binding succeeds, zero is returned. On error, −1 is returned, and errno is set appropriately.
ERRORS
The readdir() function returns a pointer to a dirent structure representing the next directory entry in the
directory stream pointed to by dir. It returns NULL on reaching the end-of-file or if an error occurred.
DESCRIPTION readdir_r
The following are general socket errors only. There may be other domain-specific error codes.
The readdir_r() function initializes the structure referenced by entry and stores a pointer to this structure
in result. On successful return, the pointer returned at *result will have the same value as the argument
entry. Upon reaching the end of the directory stream, this pointer will have the value NULL.
EBADF
The file descriptor is not a valid index in the descriptor table.
EFAULT
The socket structure address is outside the user’s address space.
The data returned by readdir() is overwritten by subsequent calls to readdir() for the same directory
stream.
ENOTSOCK
The file descriptor is not associated with a socket.
The dirent structure is defined as follows:
EISCONN
The socket is already connected.
struct dirent {
long
d_ino;
/* inode number */
off_t
d_off;
/* offset to the next dirent */
unsigned short d_reclen;
/* length of this record */
unsigned char d_type;
/* type of file */
char
d_name[256]; /* filename */
};
ECONNREFUSED
No one listening on the remote address.
ENETUNREACH
Network is unreachable.
EADDRINUSE
Local address is already in use.
RETURN VALUE
The readdir() function returns a pointer to a dirent structure, or NULL if an error occurs or end-of-file is
reached.
EAFNOSUPPORT
The passed address didn’t have the correct address family in its sa_family field.
readdir_r() returns 0 if successful or an error number to indicate failure.
EACCES, EPERM
The user tried to connect to a broadcast address without having the socket broadcast flag enabled
or the connection request failed because of a local firewall rule.
SEE ALSO
ERRORS
EACCES
Permission denied.
ENOENT
Directory does not exist, or name is an empty string.
accept(2), bind(2), listen(2), socket(2), getsockname(2)
ENOTDIR
name is not a directory.
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fopen/fdopen(3)
fopen/fdopen(3)
NAME
gets(3)
gets(3)
NAME
fopen, fdopen − stream open functions
gets, fgets − get a string from a stream
fputs, puts − output of strings
SYNOPSIS
#include <stdio.h>
SYNOPSIS
#include <stdio.h>
FILE *fopen(const char * path, const char *mode);
FILE *fdopen(int fildes, const char *mode);
char *gets(char *s);
char *fgets(char *s, int n, FILE *stream);
DESCRIPTION
The fopen function opens the file whose name is the string pointed to by path and associates a stream with
it.
The argument mode points to a string beginning with one of the following sequences (Additional characters
may follow these sequences.):
int fputs(const char *s, FILE *stream);
int puts(const char *s);
DESCRIPTION gets/fgets
The gets( ) function reads characters from the standard input stream (see intro(3)), stdin, into the array
pointed to by s, until a newline character is read or an end-of-file condition is encountered. The newline
character is discarded and the string is terminated with a null character.
r
Open text file for reading. The stream is positioned at the beginning of the file.
r+
Open for reading and writing. The stream is positioned at the beginning of the file.
w
Truncate file to zero length or create text file for writing. The stream is positioned at the beginning
of the file.
The fgets( ) function reads characters from the stream into the array pointed to by s, until n−1 characters
are read, or a newline character is read and transferred to s, or an end-of-file condition is encountered. The
string is then terminated with a null character.
w+
Open for reading and writing. The file is created if it does not exist, otherwise it is truncated. The
stream is positioned at the beginning of the file.
When using gets( ), if the length of an input line exceeds the size of s, indeterminate behavior may result.
For this reason, it is strongly recommended that gets( ) be avoided in favor of fgets( ).
a
Open for appending (writing at end of file). The file is created if it does not exist. The stream is
positioned at the end of the file.
a+
Open for reading and appending (writing at end of file). The file is created if it does not exist.
The stream is positioned at the end of the file.
The fdopen function associates a stream with the existing file descriptor, fildes. The mode of the stream
(one of the values "r", "r+", "w", "w+", "a", "a+") must be compatible with the mode of the file descriptor.
The file position indicator of the new stream is set to that belonging to fildes, and the error and end-of-file
indicators are cleared. Modes "w" or "w+" do not cause truncation of the file. The file descriptor is not
dup’ed, and will be closed when the stream created by fdopen is closed. The result of applying fdopen to a
shared memory object is undefined.
RETURN VALUE
Upon successful completion fopen, fdopen and freopen return a FILE pointer. Otherwise, NULL is
returned and the global variable errno is set to indicate the error.
RETURN VALUES
If end-of-file is encountered and no characters have been read, no characters are transferred to s and a null
pointer is returned. If a read error occurs, such as trying to use these functions on a file that has not been
opened for reading, a null pointer is returned and the error indicator for the stream is set. If end-of-file is
encountered, the EOF indicator for the stream is set. Otherwise s is returned.
ERRORS
The gets( ) and fgets( ) functions will fail if data needs to be read and:
EOVERFLOW
The file is a regular file and an attempt was made to read at or beyond the offset maximum associated with the corresponding stream.
DESCRIPTION puts/fputs
fputs() writes the string s to stream, without its trailing ’\0’.
puts() writes the string s and a trailing newline to stdout.
ERRORS
Calls to the functions described here can be mixed with each other and with calls to other output functions
from the stdio library for the same output stream.
EINVAL
The mode provided to fopen, fdopen, or freopen was invalid.
The fopen, fdopen and freopen functions may also fail and set errno for any of the errors specified for the
routine malloc(3).
RETURN VALUE
puts() and fputs() return a non - negative number on success, or EOF on error.
The fopen function may also fail and set errno for any of the errors specified for the routine open(2).
The fdopen function may also fail and set errno for any of the errors specified for the routine fcntl(2).
SEE ALSO
open(2), fclose(3), fileno(3)
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ip(7)
ip(7)
NAME
malloc(3)
malloc(3)
NAME
ip − Linux IPv4 protocol implementation
calloc, malloc, free, realloc − Allocate and free dynamic memory
SYNOPSIS
SYNOPSIS
#include <sys/socket.h>
#include <netinet/in.h>
#include <stdlib.h>
void *calloc(size_t nmemb, size_t size);
void *malloc(size_t size);
void free(void *ptr);
void *realloc(void *ptr, size_t size);
tcp_socket = socket(PF_INET, SOCK_STREAM, 0);
raw_socket = socket(PF_INET, SOCK_RAW, protocol);
udp_socket = socket(PF_INET, SOCK_DGRAM, protocol);
DESCRIPTION
DESCRIPTION
The programmer’s interface is BSD sockets compatible. For more information on sockets, see socket(7).
An IP socket is created by calling the socket(2) function as socket(PF_INET, socket_type, protocol).
Valid socket types are SOCK_STREAM to open a tcp(7) socket, SOCK_DGRAM to open a udp(7)
socket, or SOCK_RAW to open a raw(7) socket to access the IP protocol directly. protocol is the IP protocol in the IP header to be received or sent. The only valid values for protocol are 0 and IPPROTO_TCP
for TCP sockets and 0 and IPPROTO_UDP for UDP sockets.
When a process wants to receive new incoming packets or connections, it should bind a socket to a local
interface address using bind(2). Only one IP socket may be bound to any given local (address, port) pair.
When INADDR_ANY is specified in the bind call the socket will be bound to all local interfaces. When
listen(2) or connect(2) are called on a unbound socket the socket is automatically bound to a random free
port with the local address set to INADDR_ANY.
calloc() allocates memory for an array of nmemb elements of size bytes each and returns a pointer to the
allocated memory. The memory is set to zero.
malloc() allocates size bytes and returns a pointer to the allocated memory. The memory is not cleared.
free() frees the memory space pointed to by ptr, which must have been returned by a previous call to malloc(), calloc() or realloc(). Otherwise, or if free( ptr) has already been called before, undefined behaviour
occurs. If ptr is NULL, no operation is performed.
realloc() changes the size of the memory block pointed to by ptr to size bytes. The contents will be
unchanged to the minimum of the old and new sizes; newly allocated memory will be uninitialized. If ptr
is NULL, the call is equivalent to malloc(size); if size is equal to zero, the call is equivalent to free( ptr).
Unless ptr is NULL, it must have been returned by an earlier call to malloc(), calloc() or realloc().
RETURN VALUE
ADDRESS FORMAT
An IP socket address is defined as a combination of an IP interface address and a port number. The basic IP
protocol does not supply port numbers, they are implemented by higher level protocols like tcp(7).
struct sockaddr_in {
sa_family_t
sin_family;
u_int16_t
sin_port;
struct in_addr sin_addr;
};
/* Internet address. */
struct in_addr {
u_int32_t
s_addr;
};
For calloc() and malloc(), the value returned is a pointer to the allocated memory, which is suitably aligned
for any kind of variable, or NULL if the request fails.
free() returns no value.
realloc() returns a pointer to the newly allocated memory, which is suitably aligned for any kind of variable
and may be different from ptr, or NULL if the request fails. If size was equal to 0, either NULL or a
pointer suitable to be passed to free() is returned. If realloc() fails the original block is left untouched - it is
not freed or moved.
/* address family: AF_INET */
/* port in network byte order */
/* internet address */
CONFORMING TO
ANSI-C
SEE ALSO
/* address in network byte order */
brk(2), posix_memalign(3)
sin_family is always set to AF_INET. This is required; in Linux 2.2 most networking functions return
EINVAL when this setting is missing. sin_port contains the port in network byte order. The port numbers
below 1024 are called reserved ports. Only processes with effective user id 0 or the
CAP_NET_BIND_SERVICE capability may bind(2) to these sockets.
sin_addr is the IP host address. The addr member of struct in_addr contains the host interface address in
network order. in_addr should be only accessed using the inet_aton(3), inet_addr(3), inet_makeaddr(3)
library functions or directly with the name resolver (see gethostbyname(3)).
Note that the address and the port are always stored in network order. In particular, this means that you
need to call htons(3) on the number that is assigned to a port. All address/port manipulation functions in
the standard library work in network order.
SEE ALSO
sendmsg(2), recvmsg(2), socket(7), netlink(7), tcp(7), udp(7), raw(7), ipfw(7)
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pthread_cond(3)
pthread_cond(3)
NAME
pthread_cond_init,
pthread_cond_destroy,
pthread_cond_signal,
pthread_cond_wait, pthread_cond_timedwait − operations on conditions
pthread_cond_broadcast,
pthread_cond(3)
pthread_cond(3)
signaled (and thus ignored) between the time a thread locks the mutex and the time it waits on the condition
variable.
pthread_cond_timedwait atomically unlocks mutex and waits on cond, as pthread_cond_wait does, but it
also bounds the duration of the wait. If cond has not been signaled within the amount of time specified by
abstime, the mutex mutex is re-acquired and pthread_cond_timedwait returns the error ETIMEDOUT.
The abstime parameter specifies an absolute time, with the same origin as time(2) and gettimeofday(2): an
abstime of 0 corresponds to 00:00:00 GMT, January 1, 1970.
SYNOPSIS
#include <pthread.h>
pthread_cond_t cond = PTHREAD_COND_INITIALIZER;
pthread_cond_destroy destroys a condition variable, freeing the resources it might hold. No threads must
be waiting on the condition variable on entrance to pthread_cond_destroy. In the LinuxThreads implementation, no resources are associated with condition variables, thus pthread_cond_destroy actually does
nothing except checking that the condition has no waiting threads.
int pthread_cond_init(pthread_cond_t *cond, pthread_condattr_t *cond_attr);
int pthread_cond_signal(pthread_cond_t *cond);
int pthread_cond_broadcast(pthread_cond_t *cond);
CANCELLATION
int pthread_cond_wait(pthread_cond_t *cond, pthread_mutex_t *mutex);
int pthread_cond_timedwait(pthread_cond_t *cond, pthread_mutex_t *mutex, const struct timespec
*abstime);
int pthread_cond_destroy(pthread_cond_t *cond);
ASYNC-SIGNAL SAFETY
DESCRIPTION
A condition (short for ‘‘condition variable’’) is a synchronization device that allows threads to suspend
execution and relinquish the processors until some predicate on shared data is satisfied. The basic operations on conditions are: signal the condition (when the predicate becomes true), and wait for the condition,
suspending the thread execution until another thread signals the condition.
A condition variable must always be associated with a mutex, to avoid the race condition where a thread
prepares to wait on a condition variable and another thread signals the condition just before the first thread
actually waits on it.
pthread_cond_init initializes the condition variable cond, using the condition attributes specified in
cond_attr, or default attributes if cond_attr is NULL. The LinuxThreads implementation supports no
attributes for conditions, hence the cond_attr parameter is actually ignored.
Variables of type pthread_cond_t
PTHREAD_COND_INITIALIZER.
can
also
pthread_cond_wait and pthread_cond_timedwait are cancellation points. If a thread is cancelled while
suspended in one of these functions, the thread immediately resumes execution, then locks again the mutex
argument to pthread_cond_wait and pthread_cond_timedwait, and finally executes the cancellation.
Consequently, cleanup handlers are assured that mutex is locked when they are called.
be
initialized
statically,
using
the
The condition functions are not async-signal safe, and should not be called from a signal handler. In particular, calling pthread_cond_signal or pthread_cond_broadcast from a signal handler may deadlock the
calling thread.
RETURN VALUE
All condition variable functions return 0 on success and a non-zero error code on error.
ERRORS
pthread_cond_init, pthread_cond_signal, pthread_cond_broadcast, and pthread_cond_wait never
return an error code.
The pthread_cond_timedwait function returns the following error codes on error:
ETIMEDOUT
the condition variable was not signaled until the timeout specified by abstime
constant
EINTR
pthread_cond_signal restarts one of the threads that are waiting on the condition variable cond. If no
threads are waiting on cond, nothing happens. If several threads are waiting on cond, exactly one is
restarted, but it is not specified which.
pthread_cond_timedwait was interrupted by a signal
The pthread_cond_destroy function returns the following error code on error:
EBUSY
pthread_cond_broadcast restarts all the threads that are waiting on the condition variable cond. Nothing
happens if no threads are waiting on cond.
pthread_cond_wait atomically unlocks the mutex (as per pthread_unlock_mutex) and waits for the condition variable cond to be signaled. The thread execution is suspended and does not consume any CPU time
until the condition variable is signaled. The mutex must be locked by the calling thread on entrance to
pthread_cond_wait. Before returning to the calling thread, pthread_cond_wait re-acquires mutex (as per
pthread_lock_mutex).
some threads are currently waiting on cond.
AUTHOR
Xavier Leroy <[email protected]>
SEE ALSO
pthread_condattr_init(3),
nanosleep(2).
pthread_mutex_lock(3),
pthread_mutex_unlock(3),
gettimeofday(2),
Unlocking the mutex and suspending on the condition variable is done atomically. Thus, if all threads
always acquire the mutex before signaling the condition, this guarantees that the condition cannot be
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pthread_create/pthread_exit(3)
pthread_create/pthread_exit(3)
NAME
pthread_detach(3)
pthread_detach(3)
NAME
pthread_create − create a new thread / pthread_exit − terminate the calling thread
pthread_detach − put a running thread in the detached state
SYNOPSIS
SYNOPSIS
#include <pthread.h>
#include <pthread.h>
int pthread_create(pthread_t * thread, pthread_attr_t * attr, void * (*start_routine)(void *), void *
arg);
int pthread_detach(pthread_t th);
DESCRIPTION
void pthread_exit(void *retval);
pthread_detach put the thread th in the detached state. This guarantees that the memory resources consumed by th will be freed immediately when th terminates. However, this prevents other threads from synchronizing on the termination of th using pthread_join.
DESCRIPTION
pthread_create creates a new thread of control that executes concurrently with the calling thread. The new
thread applies the function start_routine passing it arg as first argument. The new thread terminates either
explicitly, by calling pthread_exit(3), or implicitly, by returning from the start_routine function. The latter
case is equivalent to calling pthread_exit(3) with the result returned by start_routine as exit code.
A thread can be created initially in the detached state, using the detachstate attribute to pthread_create(3).
In contrast, pthread_detach applies to threads created in the joinable state, and which need to be put in the
detached state later.
The attr argument specifies thread attributes to be applied to the new thread. See pthread_attr_init(3) for a
complete list of thread attributes. The attr argument can also be NULL, in which case default attributes are
used: the created thread is joinable (not detached) and has default (non real-time) scheduling policy.
After pthread_detach completes, subsequent attempts to perform pthread_join on th will fail. If another
thread is already joining the thread th at the time pthread_detach is called, pthread_detach does nothing
and leaves th in the joinable state.
pthread_exit terminates the execution of the calling thread. All cleanup handlers that have been set for the
calling thread with pthread_cleanup_push(3) are executed in reverse order (the most recently pushed handler is executed first). Finalization functions for thread-specific data are then called for all keys that have
non- NULL values associated with them in the calling thread (see pthread_key_create(3)). Finally,
execution of the calling thread is stopped.
RETURN VALUE
On success, 0 is returned. On error, a non-zero error code is returned.
ERRORS
ESRCH
The retval argument is the return value of the thread. It can be consulted from another thread using
pthread_join(3).
No thread could be found corresponding to that specified by th
EINVAL
the thread th is already in the detached state
RETURN VALUE
On success, the identifier of the newly created thread is stored in the location pointed by the thread argument, and a 0 is returned. On error, a non-zero error code is returned.
The pthread_exit function never returns.
AUTHOR
Xavier Leroy <[email protected]>
SEE ALSO
pthread_create(3), pthread_join(3), pthread_attr_setdetachstate(3).
ERRORS
EAGAIN
not enough system resources to create a process for the new thread.
EAGAIN
more than PTHREAD_THREADS_MAX threads are already active.
AUTHOR
Xavier Leroy <[email protected]>
SEE ALSO
pthread_join(3), pthread_detach(3), pthread_attr_init(3).
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pthread_mutex(3)
pthread_mutex(3)
pthread_mutex(3)
pthread_mutex(3)
performed before the mutex returns to the unlocked state.
NAME
pthread_mutex_init,
pthread_mutex_lock,
pthread_mutex_destroy − operations on mutexes
pthread_mutex_trylock,
pthread_mutex_unlock,
pthread_mutex_trylock behaves identically to pthread_mutex_lock, except that it does not block the
calling thread if the mutex is already locked by another thread (or by the calling thread in the case of a
‘‘fast’’ mutex). Instead, pthread_mutex_trylock returns immediately with the error code EBUSY.
SYNOPSIS
#include <pthread.h>
pthread_mutex_unlock unlocks the given mutex. The mutex is assumed to be locked and owned by the
calling thread on entrance to pthread_mutex_unlock. If the mutex is of the ‘‘fast’’ kind,
pthread_mutex_unlock always returns it to the unlocked state. If it is of the ‘‘recursive’’ kind, it decrements the locking count of the mutex (number of pthread_mutex_lock operations performed on it by the
calling thread), and only when this count reaches zero is the mutex actually unlocked.
pthread_mutex_t fastmutex = PTHREAD_MUTEX_INITIALIZER;
pthread_mutex_t recmutex = PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP;
pthread_mutex_t errchkmutex = PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP;
On ‘‘error checking’’ mutexes, pthread_mutex_unlock actually checks at run-time that the mutex is
locked on entrance, and that it was locked by the same thread that is now calling pthread_mutex_unlock.
If these conditions are not met, an error code is returned and the mutex remains unchanged. ‘‘Fast’’ and
‘‘recursive’’ mutexes perform no such checks, thus allowing a locked mutex to be unlocked by a thread
other than its owner. This is non-portable behavior and must not be relied upon.
int pthread_mutex_init(pthread_mutex_t *mutex, const pthread_mutexattr_t *mutexattr);
int pthread_mutex_lock(pthread_mutex_t *mutex);
int pthread_mutex_trylock(pthread_mutex_t *mutex);
pthread_mutex_destroy destroys a mutex object, freeing the resources it might hold. The mutex must be
unlocked on entrance. In the LinuxThreads implementation, no resources are associated with mutex objects,
thus pthread_mutex_destroy actually does nothing except checking that the mutex is unlocked.
int pthread_mutex_unlock(pthread_mutex_t *mutex);
int pthread_mutex_destroy(pthread_mutex_t *mutex);
RETURN VALUE
DESCRIPTION
A mutex is a MUTual EXclusion device, and is useful for protecting shared data structures from concurrent
modifications, and implementing critical sections and monitors.
pthread_mutex_init always returns 0. The other mutex functions return 0 on success and a non-zero error
code on error.
ERRORS
A mutex has two possible states: unlocked (not owned by any thread), and locked (owned by one thread). A
mutex can never be owned by two different threads simultaneously. A thread attempting to lock a mutex
that is already locked by another thread is suspended until the owning thread unlocks the mutex first.
The pthread_mutex_lock function returns the following error code on error:
EINVAL
the mutex has not been properly initialized.
pthread_mutex_init initializes the mutex object pointed to by mutex according to the mutex attributes
specified in mutexattr. If mutexattr is NULL, default attributes are used instead.
The LinuxThreads implementation supports only one mutex attributes, the mutex kind, which is either
‘‘fast’’, ‘‘recursive’’, or ‘‘error checking’’. The kind of a mutex determines whether it can be locked again
by a thread that already owns it. The default kind is ‘‘fast’’. See pthread_mutexattr_init(3) for more
information on mutex attributes.
Variables of type pthread_mutex_t can also be initialized statically, using the constants
PTHREAD_MUTEX_INITIALIZER (for fast mutexes), PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP (for recursive mutexes), and PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP (for error checking mutexes).
EDEADLK
the mutex is already locked by the calling thread (‘‘error checking’’ mutexes only).
The pthread_mutex_unlock function returns the following error code on error:
EINVAL
the mutex has not been properly initialized.
EPERM
the calling thread does not own the mutex (‘‘error checking’’ mutexes only).
The pthread_mutex_destroy function returns the following error code on error:
pthread_mutex_lock locks the given mutex. If the mutex is currently unlocked, it becomes locked and
owned by the calling thread, and pthread_mutex_lock returns immediately. If the mutex is already locked
by another thread, pthread_mutex_lock suspends the calling thread until the mutex is unlocked.
If the mutex is already locked by the calling thread, the behavior of pthread_mutex_lock depends on the
kind of the mutex. If the mutex is of the ‘‘fast’’ kind, the calling thread is suspended until the mutex is
unlocked, thus effectively causing the calling thread to deadlock. If the mutex is of the ‘‘error checking’’
kind, pthread_mutex_lock returns immediately with the error code EDEADLK. If the mutex is of the
‘‘recursive’’ kind, pthread_mutex_lock succeeds and returns immediately, recording the number of times
the calling thread has locked the mutex. An equal number of pthread_mutex_unlock operations must be
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EBUSY
the mutex is currently locked.
AUTHOR
Xavier Leroy <[email protected]>
SEE ALSO
pthread_mutexattr_init(3), pthread_mutexattr_setkind_np(3), pthread_cancel(3).
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socket(3)
socket(3)
socket − create an endpoint for communication
SYNOPSIS
SOCK_SEQPACKET sockets employ the same system calls as SOCK_STREAM sockets. The only difference is that read(2) calls will return only the amount of data requested, and any remaining in the arriving
packet will be discarded.
cc [ flag . . . ] file . . . −lsocket −lnsl [ library . . . ]
#include <sys/types.h>
#include <sys/socket.h>
SOCK_DGRAM and SOCK_RAW sockets allow datagrams to be sent to correspondents named in
int socket(int domain, int type, int protocol);
sendto(3N) calls. Datagrams are generally received with recvfrom(3N), which returns the next datagram
with its return address.
DESCRIPTION
socket( ) creates an endpoint for communication and returns a descriptor.
The domain parameter specifies a communications domain within which communication will take place;
this selects the protocol family which should be used. The protocol family generally is the same as the
address family for the addresses supplied in later operations on the socket. These families are defined in
the include file <sys/socket.h>. There must be an entry in the netconfig(4) file for at least each protocol
family and type required. If protocol has been specified, but no exact match for the tuplet family, type, protocol is found, then the first entry containing the specified family and type with zero for protocol will be
used. The currently understood formats are:
UNIX system internal protocols
PF_INET
ARPA Internet protocols
socket(3)
activity. An error is then indicated if no response can be elicited on an otherwise idle connection for a
extended period (for instance 5 minutes). A SIGPIPE signal is raised if a process sends on a broken stream;
this causes naive processes, which do not handle the signal, to exit.
NAME
PF_UNIX
socket(3)
An fcntl(2) call can be used to specify a process group to receive a SIGURG signal when the out-of-band
data arrives. It may also enable non-blocking I/O and asynchronous notification of I/O events with SIGIO
signals.
The operation of sockets is controlled by socket level options. These options are defined in the file
<sys/socket.h>. setsockopt(3N) and getsockopt(3N) are used to set and get options, respectively.
RETURN VALUES
A −1 is returned if an error occurs. Otherwise the return value is a descriptor referencing the socket.
ERRORS
The socket( ) call fails if:
The socket has the indicated type, which specifies the communication semantics. Currently defined types
are:
SOCK_STREAM
SOCK_DGRAM
SOCK_RAW
SOCK_SEQPACKET
SOCK_RDM
A SOCK_STREAM type provides sequenced, reliable, two-way connection-based byte streams. An out-ofband data transmission mechanism may be supported. A SOCK_DGRAM socket supports datagrams (connectionless, unreliable messages of a fixed (typically small) maximum length). A SOCK_SEQPACKET
socket may provide a sequenced, reliable, two-way connection-based data transmission path for datagrams
of fixed maximum length; a consumer may be required to read an entire packet with each read system call.
This facility is protocol specific, and presently not implemented for any protocol family. SOCK_RAW
sockets provide access to internal network interfaces. The types SOCK_RAW, which is available only to
the super-user, and SOCK_RDM, for which no implementation currently exists, are not described here.
EACCES
Permission to create a socket of the specified type and/or protocol is denied.
EMFILE
The per-process descriptor table is full.
ENOMEM
Insufficient user memory is available.
ENOSR
There were insufficient STREAMS resources available to complete the operation.
EPROTONOSUPPORT
The protocol type or the specified protocol is not supported within this
domain.
SEE ALSO
close(2), fcntl(2), ioctl(2), read(2), write(2), accept(3N), bind(3N), connect(3N), getsockname(3N), getsockopt(3N), listen(3N), recv(3N), setsockopt(3N), send(3N), shutdown(3N), socketpair(3N),
attributes(5), in(5), socket(5)
protocol specifies a particular protocol to be used with the socket. Normally only a single protocol exists to
support a particular socket type within a given protocol family. However, multiple protocols may exist, in
which case a particular protocol must be specified in this manner. The protocol number to use is particular
to the “communication domain” in which communication is to take place. If a protocol is specified by the
caller, then it will be packaged into a socket level option request and sent to the underlying protocol layers.
Sockets of type SOCK_STREAM are full-duplex byte streams, similar to pipes. A stream socket must be in
a connected state before any data may be sent or received on it. A connection to another socket is created
with a connect(3N) call. Once connected, data may be transferred using read(2) and write(2) calls or
some variant of the send(3N) and recv(3N) calls. When a session has been completed, a close(2) may be
performed. Out-of-band data may also be transmitted as described on the send(3N) manual page and
received as described on the recv(3N) manual page.
The communications protocols used to implement a SOCK_STREAM insure that data is not lost or duplicated. If a piece of data for which the peer protocol has buffer space cannot be successfully transmitted
within a reasonable length of time, then the connection is considered broken and calls will indicate an error
with −1 returns and with ETIMEDOUT as the specific code in the global variable errno. The protocols
optionally keep sockets “warm” by forcing transmissions roughly every minute in the absence of other
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SOS1-Klausur Manual-Auszug
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unlink(2)
unlink(2)
NAME
unlink − remove directory entry
SYNOPSIS
#include <unistd.h>
int unlink(const char * path);
DESCRIPTION
The unlink( ) function removes a link to a file. It removes the link named by the pathname pointed to by
path and decrements the link count of the file referenced by the link.
When the file’s link count becomes 0 and no process has the file open, the space occupied by the file will be
freed and the file will no longer be accessible. If one or more processes have the file open when the last
link is removed, the link will be removed before unlink( ) returns, but the removal of the file contents will
be postponed until all references to the file are closed.
RETURN VALUES
Upon successful completion, 0 is returned. Otherwise, −1 is returned and errno is set to indicate the error.
ERRORS
The unlink( ) function will fail and not unlink the file if:
EACCES
Search permission is denied for a component of the path prefix.
EACCES
Write permission is denied on the directory containing the link to be removed.
ENOENT
The named file does not exist or is a null pathname.
ENOTDIR
A component of the path prefix is not a directory.
EPERM
The named file is a directory and the effective user of the calling process is not superuser.
SEE ALSO
rm(1), close(2), link(2), open(2), rmdir(2),
SOS1-Klausur Manual-Auszug
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