【讨论】文件操作的原子性

#include <stdlib.h>#include <stdio.h>#include <string.h>#include <sys/time.h>#include <signal.h>#include <pthread.h>#include <unistd.h>#include <fcntl.h>const char *fileName = "/dev/sram-mmap"; //"test"#define SleepMs( ms ) ( usleep( (ms)*1000 ) )#define TRUE 1#define FALSE 0#define BUFLEN (65536)int createThread( pthread_t *thread, pthread_attr_t * attr, void *(*start_routine)(void *), void * arg ){ if ( pthread_create( thread, attr, start_routine, arg ) ) //成功则返回0 { return FALSE; } return TRUE; }void doing( int fd, const void *buf, int len ){ write( fd, buf, len );}void *tFun0( void * ){ char buf[BUFLEN]; memset( buf, 0x0, sizeof(buf) ); while(1 ) { int fd = open( fileName, O_RDWR ); doing( fd, buf, sizeof(buf) ); close(fd); }}void *tFun1( void * ){ char buf[BUFLEN]; memset( buf, 0x1, sizeof(buf) ); while(1 ) { int fd = open( fileName, O_RDWR ); doing( fd, buf, sizeof(buf) ); close(fd); }}void *tFun2( void * ){ char buf[BUFLEN]; memset( buf, 0x2, sizeof(buf) ); while(1 ) { int fd = open( fileName, O_RDWR ); doing( fd, buf, sizeof(buf) ); close(fd); }}void *tFun3( void * ){ char buf[BUFLEN]; memset( buf, 0x3, sizeof(buf) ); while(1 ) { int fd = open( fileName, O_RDWR ); doing( fd, buf, sizeof(buf) ); close(fd); }}int main(){ pthread_t touch_thread[10]; createThread( &touch_thread[0], NULL, tFun0, NULL ); createThread( &touch_thread[1], NULL, tFun1, NULL ); createThread( &touch_thread[2], NULL, tFun2, NULL ); createThread( &touch_thread[3], NULL, tFun3, NULL ); SleepMs(10); char oldVal = 0; char buf[BUFLEN]; memset( buf, 0x0, sizeof(buf) ); while(1 ) { int fd = open( fileName, O_RDWR ); int len = read( fd, buf, sizeof(buf) ); close(fd); char val = buf[0]; if ( oldVal != val ) { printf( "curVal = %x/n", val ); oldVal = val; } for ( int i = 1; i < len; ++i ) { if ( buf[i] != val ) { printf( "error:val = %x,buf[%d] = %x/n", val, i, buf[i] ); } } } }  

//经测试:
//(测试平台X86/Linux)
//#define BUFLEN (65536) (8192) (4097) 时，存在不一致的情况.(4096)则不存在不一致。
//说明一个块大小(4096B)的读写是原子的,不会被其他线程打断.

//(测试平台ARM/Linux,测试SRAM设备文件)
//#define BUFLEN (65536)时，没有不一致的情况。

//以上测试结果与<<【071108】文件操作的原子性>>的结果一致。