completion是一種輕量級的機制，它容許一個線程告訴另外一個線程工做已經完成。能夠利用下面的宏靜態建立completion： ?????????????????????????DECLARE_COMPLETION(my_completion);? ???????linux

若是運行時建立completion，則必須采用如下方法動態建立和初始化： ?????????????????????????struct compltion my_completion; ????????????????????????? init_completion(&my_completion);redis

completion的相關定義包含在kernel/include/Linux/completion.h中：shell

struct completion { ???????????????????????????????????? unsigned int done; ???????????????????????????????????? wait_queue_head_t wait; ???????????????????????? };app

#define COMPLETION_INITIALIZER(work) / ?????????????????????????????????????????????????????????? { 0, __WAIT_QUEUE_HEAD_INITIALIZER((work).wait) }less

#define DECLARE_COMPLETION(work) / ????????????????????????????????????????????????????? struct completion work = COMPLETION_INITIALIZER(work)測試

static inline void init_completion(struct completion *x) { ????????? x->done = 0; ????????? init_waitqueue_head(&x->wait); }ui

要等待completion，可進行以下調用： ??????????????????? void wait_for_completion(struct completion *c);this

觸發completion事件，調用： ?????????????????? void complete(struct completion *c);??? //喚醒一個等待線程 ?????????????????? void complete_all(struct completion *c);//喚醒全部的等待線程線程

為說明completion的使用方法，將《Linux設備驅動程序》一書中的complete模塊的代碼摘抄以下： /* * complete.c -- the writers awake the readers * * Copyright (C) 2003 Alessandro Rubini and Jonathan Corbet * Copyright (C) 2003 O'Reilly & Associates * * The source code in this file can be freely used, adapted, * and redistributed in source or binary form, so long as an * acknowledgment appears in derived source files.??? The citation * should list that the code comes from the book "Linux Device * Drivers" by Alessandro Rubini and Jonathan Corbet, published * by O'Reilly & Associates.???? No warranty is attached; * we cannot take responsibility for errors or fitness for use. * * $Id: complete.c,v 1.2 2004/09/26 07:02:43 gregkh Exp $ */日志

#include #include

#include ???/* current and everything */ #include ?/* printk() */ #include ??????/* everything... */ #include ???/* size_t */ #include

MODULE_LICENSE("Dual BSD/GPL");

static int complete_major = 253;//指定主設備號

DECLARE_COMPLETION(comp);

ssize_t complete_read (struct file *filp, char __user *buf, size_t count, loff_t *pos) { ???????? printk(KERN_DEBUG "process %i (%s) going to sleep/n", ???????? current->pid, current->comm); ???????? wait_for_completion(&comp); ???????? printk(KERN_DEBUG "awoken %i (%s)/n", current->pid, current->comm); ???????? return 0; /* EOF */ }

ssize_t complete_write (struct file *filp, const char __user *buf, size_t count, ??? loff_t *pos) { ???????? printk(KERN_DEBUG "process %i (%s) awakening the readers.../n", ???????? current->pid, current->comm); ???????? complete(&comp); ???????? return count;?/* succeed, to avoid retrial */ }

struct file_operations complete_fops = { ???????? .owner = THIS_MODULE, ???????? .read =??? complete_read, ???????? .write = complete_write, };

int complete_init(void) { ???????? int result;

/* ??? * Register your major, and accept a dynamic number ??? */ ??????? result = register_chrdev(complete_major, "complete", &complete_fops); ??????? if (result < 0) ??????????????? return result; ??????? if (complete_major == 0) ??????????????? complete_major = result;?/* dynamic */ ??????? return 0; }

void complete_cleanup(void) { ???????? unregister_chrdev(complete_major, "complete"); }

module_init(complete_init); module_exit(complete_cleanup);

該模塊定義了一個簡單的completion設備：任何試圖從該設備中讀取的進程都將等待，直到其余設備寫入該設備為止。編譯此模塊的Makefile以下： obj-m := complete.o KDIR := /lib/modules/$(Shell uname -r)/build PWD := $(shell pwd) default: $(MAKE) -C $(KDIR) M=$(PWD) modules clean: rm -f *.ko *.o *.mod.c

在linux終端中執行如下命令，編譯生成模塊，并進行動態加載。 #make #mknod completion c 253 0 #insmod complete.ko 再打開三個終端，一個用于讀進程： #cat completion 一個用于寫進程： #echo >completion 另外一個查看系統日志： #tail -f /var/log/messages

值得注意的是，當咱們使用的complete_all接口時，若是要重復使用一個completion結構，則必須執行 INIT_COMPLETION(struct completion c)來從新初始化它。能夠在kernel/include/linux/completion.h中找到這個宏的定義： ????????? #define INIT_COMPLETION(x) ((x).done = 0)

如下代碼對書中原有的代碼進行了一番變更，將喚醒接口由原來的complete換成了complete_all，而且為了重復利用completion結構，全部讀進程都結束后就從新初始化completion結構，具體代碼以下： #include #include

#include #include #include #include #include

MODULE_LICENSE("Dual BSD/GPL");

#undef KERN_DEBUG #define KERN_DEBUG "<1>"

static int complete_major=253; static int reader_count = 0;

DECLARE_COMPLETION(comp);

ssize_t complete_read (struct file *filp,char __user *buf,size_t count,loff_t *pos) { ?????????? printk(KERN_DEBUG "process %i (%s) going to sleep,waiting for writer/n",current->pid,current->comm); ?????????? reader_count++; ?????????? printk(KERN_DEBUG "In read ,before comletion: reader count = %d /n",reader_count); ?????????? wait_for_completion(&comp); ?????????? reader_count--; ?????????? printk(KERN_DEBUG "awoken %s (%i) /n",current->comm,current->pid); ?????????? printk(KERN_DEBUG "In read,after completion : reader count = %d /n",reader_count);

/*若是使用complete_all，則completion結構只能用一次，再次使用它時必須調用此宏進行從新初始化*/ ?????????? if(reader_count == 0) ?????????????????????? INIT_COMPLETION(comp);

return 0; }

ssize_t complete_write(struct file *filp,const char __user *buf,size_t count,loff_t *pos) { ?????????? printk(KERN_DEBUG "process %i (%s) awoking the readers.../n",current->pid,current->comm); ?????????? printk(KERN_DEBUG "In write ,before do complete_all : reader count = %d /n",reader_count);

if(reader_count != 0)?? ?????????????????? complete_all(&comp);

printk(KERN_DEBUG "In write ,after do complete_all : reader count = %d /n",reader_count);

return count; }

struct file_operations complete_fops={ ?????????? .owner = THIS_MODULE, ?????????? .read = complete_read, ?????????? .write = complete_write, };

int complete_init(void) { ?????????? int result;

result=register_chrdev(complete_major,"complete",&complete_fops); ?????????? if(result<0) ??????????????????? return result; ?????????? if(complete_major==0) ?????????????????? complete_major =result;

printk(KERN_DEBUG??? "complete driver test init! complete_major=%d/n",complete_major); ?????????? printk(KERN_DEBUG "靜態初始化completion/n");

return 0; }

void complete_exit(void) { ?????????? unregister_chrdev(complete_major,"complete"); ?????????? printk(KERN_DEBUG??? "complete driver??? is removed/n"); }

module_init(complete_init); module_exit(complete_exit);

這里測試步驟和上述同樣，只不過須要多打開幾個終端來執行多個進程同時讀操做。