在之前的文章中我們已經了解了RCU機制的原理和Linux的內核源碼，這里我們要根據RCU機制寫一個demo來展示他應該如何使用。
RCU機制的原理
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RCU（全稱為Read-Copy-Update）,它記錄所有指向共享數據的指針的使用者，當要修改構想數據時，首先創建一個副本，并在副本中修改，所喲訪問線程都離開讀臨界區后，使用者的指針指向修改后的副本，并且刪除舊數據。
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他是一種在共享數據結構中實現高效讀取和低延遲寫入操作的技術。在Linux內核中，RCU是一種基于時間窗口的鎖機制，通過充分利用多核處理器和內存系統的特性，在保證并發性的同時提供高性能。
代碼示例
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/spinlock.h>
#include <linux/kthread.h>
#include <linux/delay.h>
#include <linux/slab.h>
#include <linux/init.h>struct RCUStruct {int a;struct rcu_head rcu;
};static struct RCUStruct* Global_pointer;static struct task_struct* RCURDThread1, *RCURDThread2, *RCUWTThread;static int RCURDThreadFunc1(void* argc) {struct RCUStruct* pointer = NULL;while(1) {msleep(5);rcu_read_lock();mdelay(10);pointer = rcu_dereference(Global_pointer);if(pointer)printk("%s : read a = %d\n", __func__, pointer->a);rcu_read_unlock();}return 0;
}static int RCURDThreadFunc2(void* argc) {struct RCUStruct* pointer = NULL;while(1) {msleep(5);rcu_read_lock();mdelay(10);pointer = rcu_dereference(Global_pointer);if(pointer)printk("%s : read a = %d\n", __func__, pointer->a);rcu_read_unlock();}return 0;
}static void MyRCUDel(struct rcu_head* rcuh) {struct RCUStruct* p = container_of(rcuh, struct RCUStruct, rcu);printk("%s : a = %d\n", __func__, p->a);kfree(p);
}static int RCUWTThreadFunc(void* argc) {struct RCUStruct* old_pointer;struct RCUStruct* new_pointer;int value = (unsigned long)argc;while(1) {msleep(10);new_pointer = kmalloc(sizeof(struct RCUStruct), GFP_KERNEL);old_pointer = Global_pointer;*new_pointer = *old_pointer;new_pointer->a = value;rcu_assign_pointer(Global_pointer, new_pointer);call_rcu(&old_pointer->rcu, MyRCUDel);printk("%s : write to new %d\n", __func__, value);value++;}return 0;
}static int __init RCUFuncInit(void) {int value = 2;printk("Prompt:Successfully initialized the kernel module.\n");Global_pointer = kzalloc(sizeof(struct RCUStruct), GFP_KERNEL);RCURDThread1 = kthread_run(RCURDThreadFunc1, NULL, "RCURD1");RCURDThread2 = kthread_run(RCURDThreadFunc2, NULL, "RCURD2");RCUWTThread = kthread_run(RCUWTThreadFunc, (void*)(unsigned long)value, "RCUWT");return 0;
}static void __exit RCUFuncExit(void) {printk("Prompt:Successfully uninstalled kernel module!\n");kthread_stop(RCURDThread1);kthread_stop(RCURDThread2);kthread_stop(RCUWTThread);if(Global_pointer)kfree(Global_pointer);
}module_init(RCUFuncInit);
module_exit(RCUFuncExit);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("lenn louis");
- Makefile
obj-m:=rcu.o CURRENT_PAHT:=$(shell pwd)
LINUX_KERNEL:=$(shell uname -r) LINUX_KERNEL_PATH:=/usr/src/linux-headers-$(LINUX_KERNEL)
all:make -C $(LINUX_KERNEL_PATH) M=$(CURRENT_PAHT) modulesclean:make -C $(LINUX_KERNEL_PATH) M=$(CURRENT_PAHT) cleals運行結果
