IPC

Overview

Provides functions and structures related to inter-process communication (IPC), including signals, semaphores, and message queues.

Since:

1.0

Version:

1.0

Summary

Files

Data Structures

Macros

Typedefs

Functions

Details

Macro Definition Documentation

MINSIGSTKSZ [1/2]

#define MINSIGSTKSZ   2048

Description:

Defines the minimum size of the replaceable signal stack.

Minimum size of the replaceable signal stack.

MINSIGSTKSZ [2/2]

#define MINSIGSTKSZ   2048

Description:

Defines the minimum size of the replaceable signal stack.

Minimum size of the replaceable signal stack.

sa_handler [1/2]

#define sa_handler   _u._sa_handler

Description:

Defines the simplified writing used to indicate the __sa_handler.sa_handler field in sigaction.

Indicates the _u._sa_handler field in sigaction.

sa_handler [2/2]

#define sa_handler   __sa_handler.sa_handler

Description:

Defines the simplified writing used to indicate the __sa_handler.sa_handler field in sigaction.

Indicates the _u._sa_handler field in sigaction.

SA_NOCLDSTOP [1/2]

#define SA_NOCLDSTOP   1

Description:

Stops a child process without sending the SIGCHLD signal.

SIGCHLD is not generated when the child process is stopped.

SA_NOCLDSTOP [2/2]

#define SA_NOCLDSTOP   0x00000001

Description:

Stops a child process without sending the SIGCHLD signal.

SIGCHLD is not generated when the child process is stopped.

SA_NODEFER [1/2]

#define SA_NODEFER   0x40000000

Description:

The signals being processed are not masked during signal processing.

Signals being processed are not masked during signal processing.

SA_NODEFER [2/2]

#define SA_NODEFER   0x40000000

Description:

The signals being processed are not masked during signal processing.

Signals being processed are not masked during signal processing.

SA_ONSTACK [1/2]

#define SA_ONSTACK   0x08000000

Description:

Uses the signal stack specified by sigaltstack for signal processing.

The signal stack specified by sigaltstack is used for signal processing.

SA_ONSTACK [2/2]

#define SA_ONSTACK   0x08000000

Description:

Uses the signal stack specified by sigaltstack for signal processing.

The signal stack specified by sigaltstack is used for signal processing.

sa_sigaction [1/2]

#define sa_sigaction   _u._sa_sigaction

Description:

Defines the simplified writing used to indicate the __sa_handler.sa_sigaction field in sigaction.

Indicates the __sa_handler.sa_sigaction field in sigaction.

sa_sigaction [2/2]

#define sa_sigaction   __sa_handler.sa_sigaction

Description:

Defines the simplified writing used to indicate the __sa_handler.sa_sigaction field in sigaction.

Indicates the __sa_handler.sa_sigaction field in sigaction.

SA_SIGINFO [1/2]

#define SA_SIGINFO   4

Description:

Transfers the siginfo_t structure with the signal.

Transfers the siginfo_t with the signal.

SA_SIGINFO [2/2]

#define SA_SIGINFO   0x00000004

Description:

Transfers the siginfo_t structure with the signal.

Transfers the siginfo_t with the signal.

SIGRTMAX [1/2]

#define SIGRTMAX   [_NSIG]($api-api-SmartVision-Devices-IPC.md#ga275020780cb70a8b0cba8db5accc5d19)

Description:

End of a reliable signal.

Defines the highest available signal number.

SIGRTMAX [2/2]

#define SIGRTMAX   (__libc_current_sigrtmax())

Description:

End of a reliable signal.

Defines the highest available signal number.

SIGRTMIN [1/2]

#define SIGRTMIN   32

Description:

Start of a reliable signal.

Defines the lowest available signal number.

SIGRTMIN [2/2]

#define SIGRTMIN   (__libc_current_sigrtmin())

Description:

Start of a reliable signal.

Defines the lowest available signal number.

SIGSTKSZ [1/2]

#define SIGSTKSZ   8192

Description:

Defines the size of a signal stack.

Size of a signal stack.

SIGSTKSZ [2/2]

#define SIGSTKSZ   8192

Description:

Defines the size of a signal stack.

Size of a signal stack.

Typedef Documentation

stack_t

typedef struct [sigaltstack]($api-api-SmartVision-Devices-sigaltstack.md) [stack_t]($api-api-SmartVision-Devices-IPC.md#ga395f9ff4025fe05bb535322593abde72)

Description:

Describes a signal stack.

Describes stack information for signal processing.

Function Documentation

kill()

int kill (pid_t pid, int sig )

Description:

Sends a signal to a specified process.

Parameters:

Attention:

The default signal behavior does not support STOP and CONTINUE, and COREDUMP is not involved. SIGSTOP, SIGKILL, and SIGCONT cannot be masked. If a process is killed but its parent process is not recycled, a zombie process will be generated. After an asynchronous signal is sent to a process, the signal callback is executed only after the process is scheduled. The kernel cannot forcibly kill the process by using the signal. After the process is killed, SIGCHLD is sent to its parent process. The sending action cannot be canceled. A sleeping process cannot be woken up by a signal. For example, a process invokes the sleep function to enter the sleeping state. Currently, suspended and zombie processes cannot be forcibly killed.

Returns:

Returns 0 if the operation is successful; returns -1 and sets errno to a value in the following table if the operation fails.

mq_close()

int mq_close (mqd_t mqdes)

Description:

Closes a message queue that is no longer used.

Parameters:

Returns:

Returns 0 if the message queue is closed; returns -1 and sets errno to a value in the following table if the message queue fails to be closed.

mq_getattr()

int mq_getattr (mqd_t mqdes, struct [mq_attr]($api-api-SmartVision-Devices-mq_attr.md) * attr )

Description:

Obtains the attributes of the message queue specified by the descriptor. The values of mq_maxmsg, mq_msgsize, and mq_curmsgs are fixed.

Parameters:

Returns:

Returns 0 if the operation is successful; returns -1 and sets errno to a value in the following table if the operation fails.

mq_open()

mqd_t mq_open (const char * name, int oflag,  ... )

Description:

Creates a message queue or opens an existing message queue.

Parameters:

Attention:

The message consists of 64 bytes by default, and the maximum length of the message is 64 KB. A maximum of 1024 message queues can be created. The mq_curmsgs field in mq_attr is not supported.

Returns:

Returns a message queue descriptor if the creation or opening is successful; returns (mqd_t)-1 and sets errno to a value in the following table if the operation fails.

mq_receive()

ssize_t mq_receive (mqd_t mqdes, char * buffer, size_t size, unsigned * prioptr )

Description:

Receives a message from a specified message queue.

The message queue must have been open by mq_open().

Parameters:

Returns:

Returns the number of bytes in the received message if the message is received; returns (mqd_t)-1 and sets errno to a value in the following table if the message fails to be received.

mq_send()

int mq_send (mqd_t mqdes, const char * buffer, size_t size, unsigned prio )

Description:

Sends a message to a specified message queue.

The message queue must have been opened using mq_open().

Parameters:

Returns:

Returns 0 if the message is sent; returns -1 and sets errno to a value in the following table if the message fails to be sent.

mq_setattr()

int mq_setattr (mqd_t mqdes, const struct [mq_attr]($api-api-SmartVision-Devices-mq_attr.md) *__restrict newattr, struct [mq_attr]($api-api-SmartVision-Devices-mq_attr.md) *__restrict oldattr )

Description:

Sets the attributes of the message queue specified by the descriptor. The mq_maxmsg, mq_msgsize, and mq_curmsgs attributes cannot be modified. mq_flags supports the O_NONBLOCK attribute only.

The message queue must have been opened using mq_open().

Parameters:

Returns:

Returns 0 if the setting is successful; returns -1 and sets errno to a value in the following table if the setting fails.

mq_timedreceive()

ssize_t mq_timedreceive (mqd_t mqdes, char *__restrict buffer, size_t size, unsigned *__restrict prioptr, const struct [timespec]($api-api-SmartVision-Devices-timespec.md) *__restrict timeout )

Description:

Receives a message from the message queue, with a timeout period specified.

The message queue must have been open by mq_open().

Parameters:

Returns:

Returns the number of bytes in the message if the message is received; returns (mqd_t)-1 and sets errno to a value in the following table if the message fails to be received.

mq_timedsend()

int mq_timedsend (mqd_t mqdes, const char * buffer, size_t size, unsigned prio, const struct [timespec]($api-api-SmartVision-Devices-timespec.md) * timeout )

Description:

Sends a message to a specified message queue, with a timeout period specified.

The message queue must have been open by mq_open().

Parameters:

Returns:

Returns 0 if the message is sent; returns -1 and sets errno to a value in the following table if the message fails to be sent.

mq_unlink()

int mq_unlink (const char * name)

Description:

Decreases the reference count of the message queue by 1, or deletes the message queue if the reference count is 0.

Parameters:

Returns:

Returns 0 if the operation is successful; returns -1 and sets errno to a value in the following table if the operation fails.

psignal()

void psignal (int signum, const char * s )

Description:

Prints signal information.

This function is used to print a message on the standard error output. The message consists of the character string s, a colon, a space, a string describing the signal information signum, and a newline character. If the string s is NULL or empty, the colon and space are omitted. If signum is invalid, the message displayed will indicate an unknown signal.

Parameters:

pthread_sigmask()

int pthread_sigmask (int how, const sigset_t *__restrict set, sigset_t *__restrict oldset )

Description:

Checks or changes the signal mask of the calling thread.

Parameters:

Returns:

Returns 0 if the change is successful; returns errno as described below if the change fails.

raise()

int raise (int signum)

Description:

Sends a signal to the calling process.

Parameters:

Returns:

Returns 0 if the operation is successful; returns nonzero if the operation fails.

sem_close()

int sem_close ([sem_t]($api-api-SmartVision-Devices-sem_t.md) * sem)

Description:

Closes a specified semaphore.

Parameters:

Returns:

Returns 0 if the semaphore is closed. errno | Description

sem_destroy()

int sem_destroy ([sem_t]($api-api-SmartVision-Devices-sem_t.md) * sem)

Description:

Destroys a specified anonymous semaphore that is no longer used.

Parameters:

Returns:

Returns 0 if the destruction is successful.

sem_getvalue()

int sem_getvalue ([sem_t]($api-api-SmartVision-Devices-sem_t.md) *__restrict sem, int *__restrict sval )

Description:

Obtains the count value of a specified semaphore.

Parameters:

Returns:

Returns 0 if the operation is successful.

sem_init()

int sem_init ([sem_t]($api-api-SmartVision-Devices-sem_t.md) * sem, int pshared, unsigned int value )

Description:

Creates and initializes an anonymous semaphore.

Parameters:

Returns:

Returns 0 if the initialization is successful; returns -1 and sets errno to a value in the following table if the initialization fails.

sem_post()

int sem_post ([sem_t]($api-api-SmartVision-Devices-sem_t.md) * sem)

Description:

Increments the semaphore count by 1.

Generally, this function is used to increment the count of available shared resources when the process is to leave its critical section. This function is used together with sem_wait() to protect shared resources.

Parameters:

Returns:

Returns 0 if the operation is successful; returns -1 and sets errno to a value in the following table if the operation fails.

sem_timedwait()

int sem_timedwait ([sem_t]($api-api-SmartVision-Devices-sem_t.md) *__restrict sem, const struct [timespec]($api-api-SmartVision-Devices-timespec.md) *__restrict timeout )

Description:

Obtains the semaphore, with a timeout period specified.

If the semaphore count is greater than 0, the shared resources can be obtained and the semaphore count decreases by 1. After the function returns 0, the code execution enters the resource critical area. Otherwise, the shared resource is unavailable, the function keeps waiting, and code execution cannot enter the resource critical area. If no semaphore is obtained within the specified timeout period, -1 is returned. This function is used together with sem_post() to protect shared resources.

Parameters:

Returns:

Returns 0 if the semaphore is obtained; returns -1 and sets errno to a value in the following table if the semaphore fails to be obtained.

sem_trywait()

int sem_trywait ([sem_t]($api-api-SmartVision-Devices-sem_t.md) * sem)

Description:

Attempts to obtain the semaphore.

If the semaphore count is greater than 0, the shared resources can be obtained and the semaphore count decreases by 1. After the function returns 0, the code execution enters the resource critical area. Otherwise, the shared resource is unavailable, and the function returns -1. This function is used together with sem_post() to protect shared resources.

Parameters:

Returns:

Returns 0 if the semaphore is obtained; returns -1 and sets errno to a value in the following table if the semaphore fails to be obtained.

sem_unlink()

int sem_unlink (const char * name)

Description:

Deletes a specified semaphore.

This function is used to subtract 1 from the open count of the semaphore. If the open count is 0, this function deletes the semaphore.

Parameters:

Returns:

Returns 0 if the operation is successful; returns -1 and sets errno to a value in the following table if the operation fails.

sem_wait()

int sem_wait ([sem_t]($api-api-SmartVision-Devices-sem_t.md) * sem)

Description:

Obtains the semaphore.

If the semaphore count is greater than 0, the shared resources can be obtained and the semaphore count decreases by 1. After the function returns 0, the code execution enters the resource critical area. Otherwise, the shared resource is unavailable, the function keeps waiting, and code execution cannot enter the resource critical area. This function is used together with sem_post() to protect shared resources.

Parameters:

Returns:

Returns 0 if the semaphore is obtained; returns -1 and sets errno to a value in the following table if the semaphore fails to be obtained.

sigaction()

int [sigaction]($api-api-SmartVision-Devices-sigaction.md) (int signum, const struct [sigaction]($api-api-SmartVision-Devices-sigaction.md) *__restrict act, struct [sigaction]($api-api-SmartVision-Devices-sigaction.md) *__restrict oldact )

Description:

Checks or changes the processing action associated with a specified signal. Do not use the process creation function or thread creation function in the registered callback processing function. Otherwise, the process is abnormal. For example, do not use the fork or pthread_create function.

Parameters:

Attention:

The sa_flag field in act supports the SA_SIGINFO flag only.

Returns:

Returns 0 if the operation is successful; returns -1 and sets errno to a value in the following table if the operation fails.

sigaddset()

int sigaddset (sigset_t * set, int signum )

Description:

Adds a signal to a specified signal set.

Parameters:

Returns:

Returns 0 if the operation is successful. If set or signum is invalid, the process is abnormal.

sigandset()

int sigandset (sigset_t * dest, const sigset_t * left, const sigset_t * right )

Description:

Adds the intersection of left and right to dest.

Parameters:

Returns:

Returns 0 if the operation is successful.

sigdelset()

int sigdelset (sigset_t * set, int signum )

Description:

Delete a signal from a specified signal set.

Parameters:

Returns:

Returns 0 if the operation is successful. If set or signum is invalid, the process is abnormal.

sigemptyset()

int sigemptyset (sigset_t * set)

Description:

Clears all signals in a specified signal set.

Parameters:

Returns:

Returns 0 if the operation is successful. If set is invalid, the process is abnormal.

sigfillset()

int sigfillset (sigset_t * set)

Description:

Adds all signals to a specified signal set.

Parameters:

Returns:

Returns 0 if the operation is successful. If set is invalid, the process is abnormal.

sighold()

int sighold (int signum)

Description:

Adds the signal specified by signum to the signal mask of the calling process.

Parameters:

Returns:

Returns 0 if the operation is successful; returns -1 if the operation fails.

sigisemptyset()

int sigisemptyset (const sigset_t * set)

Description:

Checks whether the signal set is empty.

Parameters:

Returns:

Returns 0 if the set is not empty; returns 1 if the set is empty; returns -1 if the operation fails.

sigismember()

int sigismember (const sigset_t * set, int signum )

Description:

Checks whether a signal is in the signal set.

Parameters:

Returns:

Returns 0 if the signal is not in the set; returns 1 if the signal is in the set. If set or signum is invalid, the process is abnormal.

signal()

[sighandler_t]($api-api-SmartVision-Devices-IPC.md#ga754cdc0bcfffe07baa426dc252c9101a) signal (int signum, [sighandler_t]($api-api-SmartVision-Devices-IPC.md#ga754cdc0bcfffe07baa426dc252c9101a) handler )

Description:

Changes the processing action of a specified signal. Do not use the process creation function or thread creation function in the registered callback processing function. Otherwise, the process is abnormal. For example, do not use the fork or pthread_create function.

Parameters:

Returns:

Returns the pointer to the original processing action if the operation is successful; returns SIG_ERR and sets errno to a value in the following table if the operation fails.

sigorset()

int sigorset (sigset_t * dest, const sigset_t * left, const sigset_t * right )

Description:

Adds the union set of left and right to dest.

Parameters:

Returns:

Returns 0 if the operation is successful.

sigpause()

int sigpause (int signum)

Description:

Deletes the signal specified by signum from the signal mask of the calling process and suspends the process until the signal is received.

Parameters:

Attention:

After the signal is received, the original signal mask of the process is restored.

Returns:

Returns -1 and sets errno to a value in the following table.

sigpending()

int sigpending (sigset_t * set)

Description:

Obtains the signal suspended by the current thread.

Parameters:

Returns:

Returns 0 if the operation is successful; returns -1 and sets errno to a value in the following table if the operation fails.

sigprocmask()

int sigprocmask (int how, const sigset_t *__restrict set, sigset_t *__restrict oldset )

Description:

Changes the signal mask of the calling thread.

Parameters:

Returns:

Returns 0 if the change is successful; returns -1 and sets errno to a value in the following table if the change fails.

sigrelse()

int sigrelse (int signum)

Description:

Deletes the signal specified by signum from the signal mask of the calling process.

Parameters:

Returns:

Returns 0 if the deletion is successful; returns -1 if the deletion fails.

sigsuspend()

int sigsuspend (const sigset_t * mask)

Description:

Sets mask as the signal mask set of the current process and suspends the process until a signal processing action is triggered.

Parameters:

Returns:

Returns -1 and sets errno to a value in the following table.

sigtimedwait()

int sigtimedwait (const sigset_t *__restrict set, siginfo_t *__restrict info, const struct [timespec]($api-api-SmartVision-Devices-timespec.md) *__restrict timeout )

Description:

Suspends the calling thread and waits for the signal, with a timeout period specified.

This function is used to suspend execution of the calling thread until one of the signals specified in the signal set becomes pending. This function specifies the timeout behavior.

Parameters:

Attention:

The signal to be waited must be in the mask set of the current thread. Once the signal is received, it is deleted from the pending list. The waiting for the signal cannot be interrupted by other signals, that is, EINTR is not supported.

Returns:

Returns the value of the waited signal if the operation is successful; returns -1 and sets errno to a value in the following table if the operation fails.

sigwait()

int sigwait (const sigset_t *__restrict set, int *__restrict sig )

Description:

Suspends the calling thread and waits for the signal.

This function is used to suspend execution of the calling thread until one of the signals specified in the signal set becomes pending.

Parameters:

Attention:

The signal to be waited must be in the mask set of the current thread. Once the signal is received, it is deleted from the pending list.

Returns:

Returns 0 if the signal is received; returns -1 and sets errno to a value in the following table if the signal fails to be received.

sigwaitinfo()

int sigwaitinfo (const sigset_t *__restrict set, siginfo_t *__restrict info )

Description:

Suspends the calling thread and waits for the signal, with a timeout period specified.

This function is used to suspend execution of the calling thread until one of the signals specified in the signal set becomes pending. This function does not specify the timeout behavior.

Parameters:

Attention:

The signal to be waited must be in the mask set of the current thread. Once the signal is received, it is deleted from the pending list. The waiting for the signal cannot be interrupted by other signals, that is, EINTR is not supported.

Returns:

Returns the value of the waited signal if the operation is successful; returns -1 and sets errno to a value in the following table if the operation fails. errno | Description ———|——————————————-—