A DIGITAL UNIX Realtime Functional Summary

This appendix summarizes the functions that are of particular interest to realtime application developers. The source of these functions ranges from System V to POSIX 1003.1 and POSIX 1003.1b. The tables given in this appendix serve as a guide in application development, but you may need to consult the online reference pages for additional information or pointers to additional functions and commands.

The function tables are arranged according to the following categories:

Process Control Functions, Table A-1

P1003.1b Priority Scheduling Functions, Table A-2

P1003.1b Clock Functions, Table A-3

Date and Time Conversion Functions, Table A-4

P1003.1b Timer Functions, Table A-5

BSD Clock and Timer Functions, Table A-6

P1003.1b Memory Locking Functions, Table A-7

System V Memory Locking Function, Table A-8

P1003.1b Asynchronous I/O Functions, Table A-9

POSIX Synchronized I/O Functions, Table A-10

BSD Synchronized I/O Function, Table A-11

P1003.1b Message Functions, Table A-12

P1003.1b Shared Memory Functions, Table A-13

P1003.1b Semaphore Functions, Table A-14

P1003.1b Realtime Signal Functions, Table A-15

Signal Control and Other Signal Functions, Table A-16

sigsetops Primitives, Table A-17

Process Ownership Functions, Table A-18

Input and Output Functions, Table A-19

Device Control Functions, Table A-20

System Database Functions, Table A-21

Table A-1: Process Control Functions

Function Purpose

alarm Sends the calling process a SIGALRM signal after a specified number of seconds

exit Terminates the calling process

exec Runs a new image, replacing the current running image

fork Creates a new process

getenv Reads an environment list

isatty Verifies whether a file descriptor is associated with a terminal

kill Sends a signal to a process or a group of processes

malloc Allocates memory

pause Suspends the calling process until a signal of a certain type is delivered

sleep Suspends the current process either for a specified period or until a signal of a certain class is delivered

sysconf Gets the current value of a configurable system limit or option

uname Returns information about the current state of the operating system

wait Lets a parent process get status information for a child that has stopped, and delays the parent process until a signal arrives

waitpid Lets a parent process get status information for a specific child that has stopped and delays the parent process until a signal arrives from that child or that child terminates

Function	Purpose
`alarm`	Sends the calling process a SIGALRM signal after a specified number of seconds
`exit`	Terminates the calling process
`exec`	Runs a new image, replacing the current running image
`fork`	Creates a new process
`getenv`	Reads an environment list
`isatty`	Verifies whether a file descriptor is associated with a terminal
`kill`	Sends a signal to a process or a group of processes
`malloc`	Allocates memory
`pause`	Suspends the calling process until a signal of a certain type is delivered
`sleep`	Suspends the current process either for a specified period or until a signal of a certain class is delivered
`sysconf`	Gets the current value of a configurable system limit or option
`uname`	Returns information about the current state of the operating system
`wait`	Lets a parent process get status information for a child that has stopped, and delays the parent process until a signal arrives
`waitpid`	Lets a parent process get status information for a specific child that has stopped and delays the parent process until a signal arrives from that child or that child terminates

Table A-2: P1003.1b Priority Scheduling Functions

Function Purpose

sched_getscheduler Returns the scheduling policy of a specified process

sched_getparam Returns the scheduling priority of a specified process

sched_get_priority_max Returns the maximum priority allowed for a scheduling policy

sched_get_priority_min Returns the minimum priority allowed for a scheduling policy

sched_rr_get_interval Returns the current quantum for the round-robin scheduling policy

sched_setscheduler Sets the scheduling policy and priority of a specified process

sched_setparam Sets the scheduling priority of a specified process

sched_yield Yields execution to another process

Function	Purpose
`sched_getscheduler`	Returns the scheduling policy of a specified process
`sched_getparam`	Returns the scheduling priority of a specified process
`sched_get_priority_max`	Returns the maximum priority allowed for a scheduling policy
`sched_get_priority_min`	Returns the minimum priority allowed for a scheduling policy
`sched_rr_get_interval`	Returns the current quantum for the round-robin scheduling policy
`sched_setscheduler`	Sets the scheduling policy and priority of a specified process
`sched_setparam`	Sets the scheduling priority of a specified process
`sched_yield`	Yields execution to another process

Table A-3: P1003.1b Clock Functions

Function Purpose

clock_getres Returns the resolution of the specified clock

clock_gettime Returns the current value for the specified clock

clock_settime Sets the specified clock to the specified value

Function	Purpose
`clock_getres`	Returns the resolution of the specified clock
`clock_gettime`	Returns the current value for the specified clock
`clock_settime`	Sets the specified clock to the specified value

Table A-4: Date and Time Conversion Functions

Function Purpose

asctime Converts time units (hours, minutes, and seconds) into a 26-character string

ctime Converts a time in seconds since the Epoch to an ASCII string in the form generated by asctime

difftime Computes the difference between two calendar times (time1-time0) and returns the difference expressed in seconds

gmtime Converts a calendar time into time units, expressed as GMT

localtime Converts a time in seconds since the Epoch into time units

mktime Converts the time units in the tm structure pointed to by timeptr into a calendar time value with the same encoding as that of the values returned by time

tzset Sets the external variable tzname, which contains current time zone names

Function	Purpose
`asctime`	Converts time units (hours, minutes, and seconds) into a 26-character string
`ctime`	Converts a time in seconds since the Epoch to an ASCII string in the form generated by `asctime`
`difftime`	Computes the difference between two calendar times (time1-time0) and returns the difference expressed in seconds
`gmtime`	Converts a calendar time into time units, expressed as GMT
`localtime`	Converts a time in seconds since the Epoch into time units
`mktime`	Converts the time units in the `tm` structure pointed to by `timeptr` into a calendar time value with the same encoding as that of the values returned by `time`
`tzset`	Sets the external variable `tzname`, which contains current time zone names

Table A-5: P1003.1b Timer Functions

Function Purpose

nanosleep Causes the calling process to suspend execution for a specified period of time

timer_create Returns a unique timer ID used in subsequent calls to identify a timer based on the systemwide clock

timer_delete Removes a previously allocated, specified timer

timer_getoverrun Returns the timer expiration overrun count for the specified timer

timer_gettime Returns the amount of time before the specified timer is due to expire and the repetition value

timer_settime Sets the value of the specified timer to either an offset from the current clock setting or an absolute value

Function	Purpose
`nanosleep`	Causes the calling process to suspend execution for a specified period of time
`timer_create`	Returns a unique timer ID used in subsequent calls to identify a timer based on the systemwide clock
`timer_delete`	Removes a previously allocated, specified timer
`timer_getoverrun`	Returns the timer expiration overrun count for the specified timer
`timer_gettime`	Returns the amount of time before the specified timer is due to expire and the repetition value
`timer_settime`	Sets the value of the specified timer to either an offset from the current clock setting or an absolute value

Table A-6: BSD Clock and Timer Functions

Function Purpose

getitimer Returns the amount of time before the timer expires and the repetition value

gettimeofday Gets the time of day

setitimer Sets the value of the specified timer

settimeofday Sets the time of day

Function	Purpose
`getitimer`	Returns the amount of time before the timer expires and the repetition value
`gettimeofday`	Gets the time of day
`setitimer`	Sets the value of the specified timer
`settimeofday`	Sets the time of day

Table A-7: P1003.1b Memory Locking Functions

Function Purpose

mlock Locks a specified region of a process's address space

mlockall Locks all of a process's address space

munlock Unlocks a specified region of a process's address space

munlockall Unlocks all of a process's address space

Function	Purpose
`mlock`	Locks a specified region of a process's address space
`mlockall`	Locks all of a process's address space
`munlock`	Unlocks a specified region of a process's address space
`munlockall`	Unlocks all of a process's address space

Table A-8: System V Memory Locking Function

Function Purpose

plock Locks and unlocks a process, text, or data in memory

Function	Purpose
`plock`	Locks and unlocks a process, text, or data in memory

Table A-9: P1003.1b Asynchronous I/O Functions

Function Purpose

aio_cancel Cancels one or more requests pending against the file descriptor

aio_error Returns the error status of a specified operation

aio_fsync Asynchronously writes system buffers containing a file's modified data to permanent storage

aio_read Initiates a read request on the specified file descriptor

aio_return Returns the status of a completed operation

aio_suspend Suspends the calling process until at least one of the specified requests has completed

aio_write Initiates a write request to the specified file descriptor

lio_listio Initiates a list of requests

Function	Purpose
`aio_cancel`	Cancels one or more requests pending against the file descriptor
`aio_error`	Returns the error status of a specified operation
`aio_fsync`	Asynchronously writes system buffers containing a file's modified data to permanent storage
`aio_read`	Initiates a read request on the specified file descriptor
`aio_return`	Returns the status of a completed operation
`aio_suspend`	Suspends the calling process until at least one of the specified requests has completed
`aio_write`	Initiates a write request to the specified file descriptor
`lio_listio`	Initiates a list of requests

Table A-10: POSIX Synchronized I/O Functions

Function Purpose

fcntl Controls operations on files and memory objects

fdatasync Flushes modified data only from the buffer cache, providing operation completion with data integrity

fsync Flushes modified data and file control information from the buffer cache, providing operation completion with file integrity

Function	Purpose
`fcntl`	Controls operations on files and memory objects
`fdatasync`	Flushes modified data only from the buffer cache, providing operation completion with data integrity
`fsync`	Flushes modified data and file control information from the buffer cache, providing operation completion with file integrity

Table A-11: BSD Synchronized I/O Function

Function Purpose

sync Updates all file systems -- all information in memory that should be on disk is written out

Function	Purpose
`sync`	Updates all file systems -- all information in memory that should be on disk is written out

Table A-12: P1003.1b Message Functions

Function Purpose

mq_close Closes a message queue

mq_getattr Retrieves the attributes of a message queue

mq_notify Requests that a process be notified when a message is available on a queue

mq_open Opens a message queue

mq_receive Receives a message from the queue

mq_send Sends a message to a queue

mq_setattr Sets the attributes of a message queue

mq_unlink Removes a message queue

Function	Purpose
`mq_close`	Closes a message queue
`mq_getattr`	Retrieves the attributes of a message queue
`mq_notify`	Requests that a process be notified when a message is available on a queue
`mq_open`	Opens a message queue
`mq_receive`	Receives a message from the queue
`mq_send`	Sends a message to a queue
`mq_setattr`	Sets the attributes of a message queue
`mq_unlink`	Removes a message queue

Table A-13: P1003.1b Shared Memory Functions

Function Purpose

shm_open Opens a shared-memory object, returning a file descriptor

shm_unlink Removes the name of the shared-memory object

Function	Purpose
`shm_open`	Opens a shared-memory object, returning a file descriptor
`shm_unlink`	Removes the name of the shared-memory object

Table A-14: P1003.1b Semaphore Functions

Function Purpose

sem_close Deallocates the specified named semaphore

sem_destroy Destroys an unnamed semaphore

sem_getvalue Gets the value of a specified semaphore

sem_init Initializes an unnamed semaphore

sem_open Opens/creates a named semaphore for use by a process

sem_post Unlocks a locked semaphore

sem_trywait Performs a semaphore lock on a semaphore only if it can lock the semaphore without waiting for another process to unlock it

sem_unlink Removes a specified named semaphore

sem_wait Performs a semaphore lock on a semaphore

Function	Purpose
`sem_close`	Deallocates the specified named semaphore
`sem_destroy`	Destroys an unnamed semaphore
`sem_getvalue`	Gets the value of a specified semaphore
`sem_init`	Initializes an unnamed semaphore
`sem_open`	Opens/creates a named semaphore for use by a process
`sem_post`	Unlocks a locked semaphore
`sem_trywait`	Performs a semaphore lock on a semaphore only if it can lock the semaphore without waiting for another process to unlock it
`sem_unlink`	Removes a specified named semaphore
`sem_wait`	Performs a semaphore lock on a semaphore

Table A-15: POSIX 1003.1b Realtime Signal Functions

Function Purpose

sigaction Specifies the action a process takes when a particular signal is delivered

sigqueue Sends a signal, plus identifying information, to a process

sigtimedwait Waits for a signal for the specified amount of time and, if the signal is delivered within that time, returns the signal number and any identifying information the signaling process provided

sigwaitinfo Waits for a signal and, upon its delivery, returns the signal number and any identifying information the signaling process provided

Function	Purpose
`sigaction`	Specifies the action a process takes when a particular signal is delivered
`sigqueue`	Sends a signal, plus identifying information, to a process
`sigtimedwait`	Waits for a signal for the specified amount of time and, if the signal is delivered within that time, returns the signal number and any identifying information the signaling process provided
`sigwaitinfo`	Waits for a signal and, upon its delivery, returns the signal number and any identifying information the signaling process provided

Table A-16: Signal Control and Other Signal Functions

Function Purpose

signal Changes the action of a signal

sigpending Returns a signal set that represents those signals that are blocked from delivery to the process but are pending

sigprocmask Sets the process's current blocked signal mask

sigsetops Manipulates signal sets

sigsuspend Replaces the process's current blocked signal mask, waits for a signal, and, upon its delivery, calls the handler established for the signal and returns

sigwait Suspends a calling thread until a signal arrives

Function	Purpose
`signal`	Changes the action of a signal
`sigpending`	Returns a signal set that represents those signals that are blocked from delivery to the process but are pending
`sigprocmask`	Sets the process's current blocked signal mask
`sigsetops`	Manipulates signal sets
`sigsuspend`	Replaces the process's current blocked signal mask, waits for a signal, and, upon its delivery, calls the handler established for the signal and returns
`sigwait`	Suspends a calling thread until a signal arrives

Table A-17: sigsetops Primitives

Function Purpose

sigaddset Adds a signal to the signal set

sigdelset Removes a signal from the signal set

sigemptyset Initializes a signal set such that all signals are excluded

sigfillset Initializes a signal set such that all signals are included

sigismember Tests whether a signal is a member of the signal set

Function	Purpose
`sigaddset`	Adds a signal to the signal set
`sigdelset`	Removes a signal from the signal set
`sigemptyset`	Initializes a signal set such that all signals are excluded
`sigfillset`	Initializes a signal set such that all signals are included
`sigismember`	Tests whether a signal is a member of the signal set

Table A-18: Process Ownership Functions

Function Purpose

geteuid Returns the effective user ID of the calling process

getegid Returns the effective group ID of the calling process

getgid Returns the real group ID of the calling process

getpgrp Returns the process group ID of the calling process

getpid Returns the process ID of the calling process

getppid Returns the process ID of the parent of the calling process

getuid Returns the real user ID of the calling process

setgid Sets the group ID of the calling process

setsid Creates a new session, for which the calling process is the session leader

setuid Sets the user ID of the calling process

Function	Purpose
`geteuid`	Returns the effective user ID of the calling process
`getegid`	Returns the effective group ID of the calling process
`getgid`	Returns the real group ID of the calling process
`getpgrp`	Returns the process group ID of the calling process
`getpid`	Returns the process ID of the calling process
`getppid`	Returns the process ID of the parent of the calling process
`getuid`	Returns the real user ID of the calling process
`setgid`	Sets the group ID of the calling process
`setsid`	Creates a new session, for which the calling process is the session leader
`setuid`	Sets the user ID of the calling process

Table A-19: Input and Output Functions

Function Purpose

close Closes a file

dup Duplicates a file descriptor

dup2 Duplicates a file descriptor

fileno Retrieves a file descriptor

lseek Moves a pointer to a record within a file

mkfifo Creates fifo special files

open Opens a file

pipe Creates an interprocess channel

read Reads the specified number of bytes from a file

write Writes the specified number of bytes to a file

Function	Purpose
`close`	Closes a file
`dup`	Duplicates a file descriptor
`dup2`	Duplicates a file descriptor
`fileno`	Retrieves a file descriptor
`lseek`	Moves a pointer to a record within a file
`mkfifo`	Creates fifo special files
`open`	Opens a file
`pipe`	Creates an interprocess channel
`read`	Reads the specified number of bytes from a file
`write`	Writes the specified number of bytes to a file

Table A-20: Device Control Functions

Function Purpose

cfgetispeed Retrieves the input baud rate for a terminal

cfgetospeed Retrieves the output baud rate for a terminal

cfsetispeed Sets the input baud rate for a terminal

cfsetospeed Sets the output baud rate for a terminal

isatty Verifies whether a file descriptor is associated with a terminal

tcdrain Causes a process to wait until all output has been transmitted

tcflow Suspends or restarts the transmission or reception of data

tcflush Discards data that is waiting to be transmitted

tcgetattr Retrieves information on the state of a terminal

tcsendbreak Sends a break character for a specified amount of time

tcsetattr Applies a set of attributes to a terminal

Function	Purpose
`cfgetispeed`	Retrieves the input baud rate for a terminal
`cfgetospeed`	Retrieves the output baud rate for a terminal
`cfsetispeed`	Sets the input baud rate for a terminal
`cfsetospeed`	Sets the output baud rate for a terminal
`isatty`	Verifies whether a file descriptor is associated with a terminal
`tcdrain`	Causes a process to wait until all output has been transmitted
`tcflow`	Suspends or restarts the transmission or reception of data
`tcflush`	Discards data that is waiting to be transmitted
`tcgetattr`	Retrieves information on the state of a terminal
`tcsendbreak`	Sends a break character for a specified amount of time
`tcsetattr`	Applies a set of attributes to a terminal

Table A-21: System Database Functions

Function Purpose

getgrgid Returns group information when passed a group ID

getgrnam Returns group information when passed a group name

getpwnam Returns user information when passed a user name

getpwuid Returns user information when passed a user ID

Function	Purpose
`getgrgid`	Returns group information when passed a group ID
`getgrnam`	Returns group information when passed a group name
`getpwnam`	Returns user information when passed a user name
`getpwuid`	Returns user information when passed a user ID