| PORT_ASSOCIATE(3C) | Standard C Library Functions | PORT_ASSOCIATE(3C) |
int port_associate(int port, int source, uintptr_t object,
int events, void *user);
int port_dissociate(int port, int source, uintptr_t object);
The objects that can be associated with a port by way of the port_associate() function are objects of type PORT_SOURCE_FD and PORT_SOURCE_FILE. Objects of other types have type-specific association mechanisms. A port_notify_t structure, defined in <port.h>, is used to specify the event port and an application-defined cookie to associate with these event sources. See port_create(3C) and signal.h(3HEAD).
The port_notify_t structure contains the following members:
Objects of type PORT_SOURCE_FD are file descriptors. The event types for PORT_SOURCE_FD objects are described in poll(2). At most one event notification will be generated per associated file descriptor. For example, if a file descriptor is associated with a port for the POLLRDNORM event and data is available on the file descriptor at the time the port_associate() function is called, an event is immediately sent to the port. If data is not yet available, one event is sent to the port when data first becomes available.
When an event for a PORT_SOURCE_FD object is retrieved, the object no longer has an association with the port. The event can be processed without the possibility that another thread can retrieve a subsequent event for the same object. After processing of the file descriptor is completed, the port_associate() function can be called to reassociate the object with the port.
Objects of type PORT_SOURCE_FILE are pointer to the structure file_obj defined in <sys/port.h>. This event source provides event notification when the specified file/directory is accessed, modified, truncated or when its status changes. The path name of the file/directory to be watched is passed in the struct file_obj along with the access, modification, and change time stamps acquired from a stat(2) call. If the file name is a symbolic link, it is followed by default. The FILE_NOFOLLOW needs to be passed in along with the specified events if the symbolic link itself needs to be watched and lstat() needs to be used to get the file status of the symbolic link file.
The struct file_obj contains the following elements:
At the time the port_associate() function is called, the time stamps passed in the structure file_obj are compared with the file or directory's current time stamps and, if there has been a change, an event is immediately sent to the port. If not, an event will be sent when such a change occurs.
The event types that can be specified at port_associate() time for PORT_SOURCE_FILE are FILE_ACCESS, FILE_MODIFIED, FILE_ATTRIB, and FILE_TRUNC. The first three of these correspond to the three time stamps: an fo_atime change results in the FILE_ACCESS event, an fo_mtime change results in the FILE_MODIFIED event, and an fo_ctime change results in the FILE_ATTRIB event. If the operation that induced the time stamp update also truncated the file, FILE_TRUNC will be set in the resulting event.
The following exception events are delivered when they occur. These event types cannot be filtered.
At most one event notification will be generated per associated file_obj. When the event for the associated file_obj is retrieved, the object is no longer associated with the port. The event can be processed without the possibility that another thread can retrieve a subsequent event for the same object. The port_associate() can be called to reassociate the file_obj object with the port.
The association is also removed if the port gets closed or when port_dissociate() is called.
The parent and child processes are allowed to retrieve events from file descriptors shared after a call to fork(2). The process performing the first association with a port (parent or child process) is designated as the owner of the association. Only the owner of an association is allowed to dissociate the file descriptor from a port. The association is removed if the owner of the association closes the port .
On NFS file systems, events from only the client side (local) access/modifications to files or directories will be delivered.
The port_associate() function will fail if:
The port_dissociate() function will fail if:
The following example retrieves data from a pipe file descriptor.
int port;
int fd;
int error;
int index;
void *mypointer;
port_event_t pev;
struct timespec_t timeout;
char rbuf[STRSIZE];
int fds[MAXINDEX];
/* create a port */
port = port_create();
for (index = 0; index < MAXINDEX; index++) {
error = mkfifo(name[index], S_IRWXU | S_IRWXG | S_IRWXO);
if (error)
/* handle error code */
fds[index] = open(name[index], O_RDWR);
/* associate pipe file descriptor with the port */
error = port_associate(port, PORT_SOURCE_FD, fds[index],
POLLIN, mypointer);
}
...
timeout.tv_sec = 1; /* user defined */
timeout.tv_nsec = 0;
/* loop to retrieve data from the list of pipe file descriptors */
for (...) {
/* retrieve a single event */
error = port_get(port, &pev, &timeout);
if (error) {
/* handle error code */
}
fd = pev.portev_object;
if (read(fd, rbuf, STRSIZE)) {
/* handle error code */
}
if (fd-still-accepting-data) {
/*
* re-associate the file descriptor with the port.
* The re-association is required for the
* re-activation of the data detection.
* Internals events and user arguments are set to the
* new (or the same) values delivered here.
*/
error = port_associate(port, PORT_SOURCE_FD, fd, POLLIN,
pev.portev_user);
} else {
/*
* If file descriptor is no longer required,
* - it can remain disabled but still associated with
* the port, or
* - it can be dissociated from the port.
*/
}
Example 2 Bind AIO transaction to a specific port.
The following example binds the AIO transaction to a specific port.
int port;
port_notify_t pn;
aiocb_t aiocb;
aiocb_t *aiocbp;
void *mypointer;
int error;
int my_errno;
int my_status;
struct timespec_t timeout;
port_event_t pev;
port = port_create();
...
/* fill AIO specific part */
aiocb.aio_fildes = fd;
aiocb.aio_nbytes = BUFSIZE;
aiocb.aio_buf = bufp;
aiocb.aio_offset = 0;
/* port specific part */
pn.portnfy_port = port;
pn.portnfy_user = mypointer;
aiocb.aio_sigevent.sigev_notify = SIGEV_PORT;
aiocb.aio_sigevent.sigev_value.sival_ptr = &pn
/*
* The aio_read() function binds internally the asynchronous I/O
* transaction with the port delivered in port_notify_t.
*/
error = aio_read(&aiocb);
timeout.tv_sec = 1; /* user defined */
timeout.tv_nsec = 0;
/* retrieve a single event */
error = port_get(port, &pev, &timeout);
if (error) {
/* handle error code */
}
/*
* pev.portev_object contains a pointer to the aiocb structure
* delivered in port_notify_t (see aio_read()).
*/
aiocbp = pev.portev_object;
/* check error code and return value in
my_errno = aio_error(aiocbp);
...
my_status = aio_return(aiocbp);
...
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
| Architecture | all |
| Interface Stability | Committed |
| MT-Level | Safe |
| August 8, 2015 |