Книга: Real-Time Concepts for Embedded Systems
6.3.1 Creating and Deleting Semaphores
6.3.1 Creating and Deleting Semaphores
Table 6.1 identifies the operations used to create and delete semaphores.
Table 6.1: Semaphore creation and deletion operations.
| Operation | Description |
|---|---|
| Create | Creates a semaphore |
| Delete | Deletes a semaphore |
Several things must be considered, however, when creating and deleting semaphores. If a kernel supports different types of semaphores, different calls might be used for creating binary, counting, and mutex semaphores, as follows:
· binary - specify the initial semaphore state and the task-waiting order.
· counting - specify the initial semaphore count and the task-waiting order.
· mutex - specify the task-waiting order and enable task deletion safety, recursion, and priority-inversion avoidance protocols, if supported.
Semaphores can be deleted from within any task by specifying their IDs and making semaphore-deletion calls. Deleting a semaphore is not the same as releasing it. When a semaphore is deleted, blocked tasks in its task-waiting list are unblocked and moved either to the ready state or to the running state (if the unblocked task has the highest priority). Any tasks, however, that try to acquire the deleted semaphore return with an error because the semaphore no longer exists.
Additionally, do not delete a semaphore while it is in use (e.g., acquired). This action might result in data corruption or other serious problems if the semaphore is protecting a shared resource or a critical section of code.
Оглавление книги
- Creating an OS Design
- Разработка приложений баз данных InterBase на Borland Delphi
- Open Source Insight and Discussion
- Introduction to Microprocessors and Microcontrollers
- Chapter 6. Traversing of tables and chains
- Chapter 8. Saving and restoring large rule-sets
- Chapter 11. Iptables targets and jumps
- Chapter 5 Installing and Configuring VirtualCenter 2.0
- Chapter 16. Commercial products based on Linux, iptables and netfilter
- Appendix A. Detailed explanations of special commands
- Appendix B. Common problems and questions
- Appendix E. Other resources and links