读数据的线程同步问题
现在要用多个线程来读取同一个数据，而且读完之后要删除该数据项，需要做线程同步吗？如果不做线程同步的话可能会多个线程读取到同一个数据。如果要做线程同步应该怎么写代码？要纯C的代码，不要用到"windows.h"里面的东西或者其他的window库
[解决办法]
标准C代码不支持临界区
不过可以用volatile来代替，volatile的意思是每次都从内存中获取数据，不过这样用比较危险，建议不要用
[解决办法]
仅供参考
//循环向a函数每次发送200个字节长度（这个是固定的）的buffer,//a函数中需要将循环传进来的buffer，组成240字节（也是固定的）的新buffer进行处理，//在处理的时候每次从新buffer中取两个字节打印#include <stdio.h>#include <stdlib.h>#include <string.h>#include <windows.h>#include <process.h>#include <io.h>//Log{#define MAXLOGSIZE 10000000#define ARRSIZE(x) (sizeof(x)/sizeof(x[0]))#include <time.h>#include <sys/timeb.h>#include <stdarg.h>char logfilename1[]="MyLog1.log";char logfilename2[]="MyLog2.log";char logstr[16000];char datestr[16];char timestr[16];char mss[4];CRITICAL_SECTION cs_log;FILE *flog;void Lock(CRITICAL_SECTION *l) { EnterCriticalSection(l);}void Unlock(CRITICAL_SECTION *l) { LeaveCriticalSection(l);}void LogV(const char *pszFmt,va_list argp) { struct tm *now; struct timeb tb; if (NULL==pszFmt||0==pszFmt[0]) return; if (-1==_vsnprintf(logstr,ARRSIZE(logstr),pszFmt,argp)) logstr[ARRSIZE(logstr)-1]=0; ftime(&tb); now=localtime(&tb.time); sprintf(datestr,"%04d-%02d-%02d",now->tm_year+1900,now->tm_mon+1,now->tm_mday); sprintf(timestr,"%02d:%02d:%02d",now->tm_hour ,now->tm_min ,now->tm_sec ); sprintf(mss,"%03d",tb.millitm); printf("%s %s.%s %s",datestr,timestr,mss,logstr); flog=fopen(logfilename1,"a"); if (NULL!=flog) { fprintf(flog,"%s %s.%s %s",datestr,timestr,mss,logstr); if (ftell(flog)>MAXLOGSIZE) { fclose(flog); if (rename(logfilename1,logfilename2)) { remove(logfilename2); rename(logfilename1,logfilename2); } flog=fopen(logfilename1,"a"); if (NULL==flog) return; } fclose(flog); }}void Log(const char *pszFmt,...) { va_list argp; Lock(&cs_log); va_start(argp,pszFmt); LogV(pszFmt,argp); va_end(argp); Unlock(&cs_log);}//Log}#define ASIZE 200#define BSIZE 240#define CSIZE 2char Abuf[ASIZE];char Cbuf[CSIZE];CRITICAL_SECTION cs_HEX ;CRITICAL_SECTION cs_BBB ;struct FIFO_BUFFER { int head; int tail; int size; char data[BSIZE];} BBB;int No_Loop=0;void HexDump(int cn,char *buf,int len) { int i,j,k; char binstr[80]; Lock(&cs_HEX); for (i=0;i<len;i++) { if (0==(i%16)) { sprintf(binstr,"%03d %04x -",cn,i); sprintf(binstr,"%s %02x",binstr,(unsigned char)buf[i]); } else if (15==(i%16)) { sprintf(binstr,"%s %02x",binstr,(unsigned char)buf[i]); sprintf(binstr,"%s ",binstr); for (j=i-15;j<=i;j++) { sprintf(binstr,"%s%c",binstr,('!'<buf[j]&&buf[j]<='~')?buf[j]:'.'); } Log("%s\n",binstr); } else { sprintf(binstr,"%s %02x",binstr,(unsigned char)buf[i]); } } if (0!=(i%16)) { k=16-(i%16); for (j=0;j<k;j++) { sprintf(binstr,"%s ",binstr); } sprintf(binstr,"%s ",binstr); k=16-k; for (j=i-k;j<i;j++) { sprintf(binstr,"%s%c",binstr,('!'<buf[j]&&buf[j]<='~')?buf[j]:'.'); } Log("%s\n",binstr); } Unlock(&cs_HEX);}int GetFromRBuf(int cn,CRITICAL_SECTION *cs,FIFO_BUFFER *fbuf,char *buf,int len) { int lent,len1,len2; lent=0; Lock(cs); if (fbuf->size>=len) { lent=len; if (fbuf->head+lent>BSIZE) { len1=BSIZE-fbuf->head; memcpy(buf ,fbuf->data+fbuf->head,len1); len2=lent-len1; memcpy(buf+len1,fbuf->data ,len2); fbuf->head=len2; } else { memcpy(buf ,fbuf->data+fbuf->head,lent); fbuf->head+=lent; } fbuf->size-=lent; } Unlock(cs); return lent;}void thdB(void *pcn) { char *recv_buf; int recv_nbytes; int cn; int wc; int pb; cn=(int)pcn; Log("%03d thdB thread begin...\n",cn); while (1) { Sleep(10); recv_buf=(char *)Cbuf; recv_nbytes=CSIZE; wc=0; while (1) { pb=GetFromRBuf(cn,&cs_BBB,&BBB,recv_buf,recv_nbytes); if (pb) { Log("%03d recv %d bytes\n",cn,pb); HexDump(cn,recv_buf,pb); Sleep(1); } else { Sleep(1000); } if (No_Loop) break;// wc++; if (wc>3600) Log("%03d %d==wc>3600!\n",cn,wc); } if (No_Loop) break;// }}int PutToRBuf(int cn,CRITICAL_SECTION *cs,FIFO_BUFFER *fbuf,char *buf,int len) { int lent,len1,len2; Lock(cs); lent=len; if (fbuf->size+lent>BSIZE) { lent=BSIZE-fbuf->size; } if (fbuf->tail+lent>BSIZE) { len1=BSIZE-fbuf->tail; memcpy(fbuf->data+fbuf->tail,buf ,len1); len2=lent-len1; memcpy(fbuf->data ,buf+len1,len2); fbuf->tail=len2; } else { memcpy(fbuf->data+fbuf->tail,buf ,lent); fbuf->tail+=lent; } fbuf->size+=lent; Unlock(cs); return lent;}void thdA(void *pcn) { char *send_buf; int send_nbytes; int cn; int wc; int a; int pa; cn=(int)pcn; Log("%03d thdA thread begin...\n",cn); a=0; while (1) { Sleep(100); memset(Abuf,a,ASIZE); a=(a+1)%256; if (16==a) {No_Loop=1;break;}//去掉这句可以让程序一直循环直到按Ctrl+C或Ctrl+Break或当前目录下存在文件No_Loop send_buf=(char *)Abuf; send_nbytes=ASIZE; Log("%03d sending %d bytes\n",cn,send_nbytes); HexDump(cn,send_buf,send_nbytes); wc=0; while (1) { pa=PutToRBuf(cn,&cs_BBB,&BBB,send_buf,send_nbytes); Log("%03d sent %d bytes\n",cn,pa); HexDump(cn,send_buf,pa); send_buf+=pa; send_nbytes-=pa; if (send_nbytes<=0) break;// Sleep(1000); if (No_Loop) break;// wc++; if (wc>3600) Log("%03d %d==wc>3600!\n",cn,wc); } if (No_Loop) break;// }}int main() { InitializeCriticalSection(&cs_log ); Log("Start===========================================================\n"); InitializeCriticalSection(&cs_HEX ); InitializeCriticalSection(&cs_BBB ); BBB.head=0; BBB.tail=0; BBB.size=0; _beginthread((void(__cdecl *)(void *))thdA,0,(void *)1); _beginthread((void(__cdecl *)(void *))thdB,0,(void *)2); if (!access("No_Loop",0)) { remove("No_Loop"); if (!access("No_Loop",0)) { No_Loop=1; } } while (1) { Sleep(1000); if (No_Loop) break;// if (!access("No_Loop",0)) { No_Loop=1; } } Sleep(3000); DeleteCriticalSection(&cs_BBB ); DeleteCriticalSection(&cs_HEX ); Log("End=============================================================\n"); DeleteCriticalSection(&cs_log ); return 0;}
[解决办法]
仅供参考
#include <stdio.h>#include <stdlib.h>#include <string.h>#ifdef WIN32 #include <windows.h> #include <io.h> #include <process.h> #define MYVOID void#else #include <unistd.h> #include <sys/time.h> #include <pthread.h> #define CRITICAL_SECTION pthread_mutex_t #define _vsnprintf vsnprintf #define MYVOID void *#endif//Log{#define MAXLOGSIZE 20000000#define ARRSIZE(x) (sizeof(x)/sizeof(x[0]))#include <time.h>#include <sys/timeb.h>#include <stdarg.h>char logfilename1[]="MyLog1.log";char logfilename2[]="MyLog2.log";char logstr[16000];char datestr[16];char timestr[16];char mss[4];CRITICAL_SECTION cs_log;FILE *flog;#ifdef WIN32void Lock(CRITICAL_SECTION *l) { EnterCriticalSection(l);}void Unlock(CRITICAL_SECTION *l) { LeaveCriticalSection(l);}void sleep_ms(int ms) { Sleep(ms);}#elsevoid Lock(CRITICAL_SECTION *l) { pthread_mutex_lock(l);}void Unlock(CRITICAL_SECTION *l) { pthread_mutex_unlock(l);}void sleep_ms(int ms) { usleep(ms*1000);}#endifvoid LogV(const char *pszFmt,va_list argp) { struct tm *now; struct timeb tb; if (NULL==pszFmt||0==pszFmt[0]) return; if (-1==_vsnprintf(logstr,ARRSIZE(logstr),pszFmt,argp)) logstr[ARRSIZE(logstr)-1]=0; ftime(&tb); now=localtime(&tb.time); sprintf(datestr,"%04d-%02d-%02d",now->tm_year+1900,now->tm_mon+1,now->tm_mday); sprintf(timestr,"%02d:%02d:%02d",now->tm_hour ,now->tm_min ,now->tm_sec ); sprintf(mss,"%03d",tb.millitm); printf("%s %s.%s %s",datestr,timestr,mss,logstr); flog=fopen(logfilename1,"a"); if (NULL!=flog) { fprintf(flog,"%s %s.%s %s",datestr,timestr,mss,logstr); if (ftell(flog)>MAXLOGSIZE) { fclose(flog); if (rename(logfilename1,logfilename2)) { remove(logfilename2); rename(logfilename1,logfilename2); } flog=fopen(logfilename1,"a"); if (NULL==flog) return; } fclose(flog); }}void Log(const char *pszFmt,...) { va_list argp; Lock(&cs_log); va_start(argp,pszFmt); LogV(pszFmt,argp); va_end(argp); Unlock(&cs_log);}//Log}static int volatile No_Loop=0;static int volatile gLock = 0;static int volatile gCounter = 0;MYVOID testThread(void *pcn) { int n,i; n=(int)pcn; while (1) { if (No_Loop==2) { for (i = 0; i < 1000000; ) { //以下代码无效// if ( 0 == gLock ) {// gLock = n;// if( gLock == n ) {// ++i;// ++gCounter;// //if (i%100000==0) Log("%d %d\n",n,gCounter);// gLock = 0;// //if (i%100000==0) sleep_ms(10*(rand()%50));// continue;// } else sleep_ms(100);// } else sleep_ms(100); //应改为以下代码 InterlockedCompareExchange((void **)&gLock, (void *)n, 0); if( gLock == n ) { ++i; ++gCounter; if (i%100000==0) Log("%d %d\n",n,gCounter); InterlockedExchange((long *)&gLock, 0); if (i%100000==0) sleep_ms(10*(rand()%50)); continue; } else sleep_ms(100); } sleep_ms(1000); No_Loop=1; } }}int main(int argc,char * argv[]) { int i; srand(time(NULL));#ifdef WIN32 InitializeCriticalSection(&cs_log);#else pthread_mutex_init(&cs_log,NULL); pthread_t threads[4];// void *thread_result; int threadsN; int rc;#endif Log("=========BEGIN==================\n");#ifdef WIN32 _beginthread((void(__cdecl *)(void *))testThread,0,(void *)1); _beginthread((void(__cdecl *)(void *))testThread,0,(void *)2); _beginthread((void(__cdecl *)(void *))testThread,0,(void *)3); _beginthread((void(__cdecl *)(void *))testThread,0,(void *)4);#else threadsN=0; rc=pthread_create(&(threads[threadsN++]),NULL,testThread,(void *)1);if (rc) Log("%d=pthread_create %d error!\n",rc,threadsN-1); rc=pthread_create(&(threads[threadsN++]),NULL,testThread,(void *)2);if (rc) Log("%d=pthread_create %d error!\n",rc,threadsN-1); rc=pthread_create(&(threads[threadsN++]),NULL,testThread,(void *)3);if (rc) Log("%d=pthread_create %d error!\n",rc,threadsN-1); rc=pthread_create(&(threads[threadsN++]),NULL,testThread,(void *)4);if (rc) Log("%d=pthread_create %d error!\n",rc,threadsN-1);#endif sleep_ms(1000); No_Loop=2; i=0; while (1) { sleep_ms(1000); if (No_Loop==1) break;// } sleep_ms(1000); Log("Result: %d\n",gCounter); Log("=========END====================\n");#ifdef WIN32 DeleteCriticalSection(&cs_log);#else pthread_mutex_destroy(&cs_log);#endif return 0;}
[解决办法]
1. 多个线程读同一个数据不会有问题的，问题会出在一边删除数据一边正在读,可能会造成读到的数据混乱.要保证删除之前没有线程在用或是删除之后数据仍然有效(不过不推荐)就可以了.
2. 你既然能够让程序跑起多线程来，说明你已经使用到了操作系统的多线程创建函数,为什么不再用一个操作系统提供的多线程同步操作呢.
[解决办法]
貌似CRT库对这个没有支持，可以在C里插些汇编搞定