Semaphore

Offers interface for accessing semaphores. Semaphores are used to signal events between different thread_t or process_t. If a process executes another program the semaphore is closed. To prevent this an inherit function would be need and a way to transfer the id and init from id function.

Summary

Semaphore	Offers interface for accessing semaphores.
Copyright	This program is free software.
Files
C-kern/api/platform/sync/semaphore.h	Header file of Semaphore.
C-kern/platform/Linux/sync/semaphore.c	Linux implementation file Semaphore Linuximpl.
Types
struct semaphore_t	Export semaphore_t.
Functions
test
unittest_platform_sync_semaphore	Tests system semaphore functionality.
semaphore_t	Describes a system semaphore used between threads.
lifetime
semaphore_FREE	Static initializer.
init_semaphore	Initializes a semaphore.
free_semaphore	Wakes up any waiting threads and frees the associated resources.
synchronize
signal_semaphore	Wakes up signal_count waiters.
wait_semaphore	Waits until a signal is received.

Copyright

This program is free software. You can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

Author

Files

C-kern/api/platform/sync/semaphore.h

Header file of Semaphore.

C-kern/platform/Linux/sync/semaphore.c

Linux implementation file Semaphore Linuximpl.

Types

struct semaphore_t

typedef struct semaphore_t semaphore_t

Export semaphore_t.

Functions

Summary

test
unittest_platform_sync_semaphore	Tests system semaphore functionality.

test

unittest_platform_sync_semaphore

int unittest_platform_sync_semaphore( void )

Tests system semaphore functionality.

semaphore_t

struct semaphore_t

Describes a system semaphore used between threads. This thread safe object allows to wait for or to send a signal to one or more waiters.

Summary

lifetime
semaphore_FREE	Static initializer.
init_semaphore	Initializes a semaphore.
free_semaphore	Wakes up any waiting threads and frees the associated resources.
synchronize
signal_semaphore	Wakes up signal_count waiters.
wait_semaphore	Waits until a signal is received.

lifetime

semaphore_FREE

#define semaphore_FREE { sys_semaphore_FREE }

Static initializer.

init_semaphore

int init_semaphore( /*out*/semaphore_t * semaobj,
uint16_t init_signal_count )

Initializes a semaphore. The internal signal counter is set to init_signal_count. The next init_signal_count calls to wait_semaphore therefore succeed without waiting.

free_semaphore

int free_semaphore( semaphore_t * semaobj )

Wakes up any waiting threads and frees the associated resources. Make sure that no other thread which is not already waiting on the semaphore accesses it after free_semaphore has been called.

synchronize

signal_semaphore

int signal_semaphore( semaphore_t * semaobj,
uint32_t signal_count )

Wakes up signal_count waiters. Or the next signal_count calls to wait_semaphore succeed without waiting. Internally this function increments a signal counter with the number signal_count. Calling this function signal_count times with a value of 1 has therefore the same effect. If the internal counter would overflow the signal function waits until at least that many calls to wait_semaphore has been done so that adding signal_count to the counter does no more produce an overflow. On Linux a 64bit counter is used internally.

wait_semaphore

int wait_semaphore( semaphore_t * semaobj )

Waits until a signal is received. This functions waits until the internal counter becomes greater zero. The signal counter is decremented by one and the function returns with success (0).