LiteOS-Reading/src/doc/LiteOS_Kernel_Developer_Guide_en/development-guidelines-37.md

Development Guidelines

Usage Scenarios

A spinlock provides a mutual exclusion mechanism to prevent two tasks from accessing the same shared resource at the same time.

Functions

The spinlock module of Huawei LiteOS provides the following functions. For details about the APIs, see the API reference.

Function Category	API	Description
Spinlock initialization	LOS_SpinInit	Dynamically initializes a spinlock.
	SPIN_LOCK_INIT	Statically initializes a spinlock.
Spinlock request and release	LOS_SpinLock	Requests a specified spinlock. If the spinlock cannot be obtained, the system waits in a loop.
	LOS_SpinTrylock	Attempts to request a specified spinlock. If the spinlock cannot be obtained, a failure message is returned, and the system does not wait in a loop.
	LOS_SpinUnlock	Releases a spinlock.
Spinlock request and release (with disabled interrupt)	LOS_SpinLockSave	Requests a spinlock after the interrupt is disabled.
	LOS_SpinUnlockRestore	Releases a spinlock and restores the interrupt.
Spinlock holding status	LOS_SpinHeld	Checks whether a spinlock is held.

Development Process

The typical spinlock development process is as follows:

1. Spinlocks depend on the SMP. Run the make menuconfig command and choose Kernel > Enable Kernel SMP to configure the spinlock.

   Configuration Item	Description	Value Range	Default Value	Dependency
   LOSCFG_KERNEL_SMP	Whether to enable the SMP.	YES/NO	YES	Multi-core hardware is supported.
   LOSCFG_KERNEL_SMP_CORE_NUM	Number of cores in the multi-core scenario.	Depends on the architecture.	2	None

2. To create a spinlock, call the LOS_SpinInit API to initialize the spinlock, or call SPIN_LOCK_INIT API to initialize the spinlock of the static memory.

3. Call the LOS_SpinLock, LOS_SpinTrylock, or LOS_SpinLockSave API to request a spinlock. If the request is successful, the code for lock protection is executed. If the request fails, the system enters a busy loop till a spinlock is obtained.

4. Call the LOS_SpinUnlock/LOS_SpinUnlockRestore API to release a spinlock. After the lock protection code is executed, the corresponding spinlock is released, so that other cores can request the spinlock.