# 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.
Spinlock initialization	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.
Spinlock request and release (with disabled interrupt)	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.