策略的更新、加載與同步

????????C語言的C庫提供了策略的更新、加載與同步的方法，這里引入多線程，達到區分讀寫任務（生產者——消費者模型）的目的。

示例：

/*@brief check strategy to update, reload, synchronized to read(stoped by SIGINT)@author wen`xuanpei@email 15873152445@163.com(query for any question here)
*/
#include <pthread.h>//pthread_(create|exit), pthread_rwlock_(init|destroy|wrlock|rdlock|unlock),
#include <unistd.h>//sleep,
#include <errno.h>//<cerrno>//errno,
//stat
#include <sys/types.h>
#include <sys/stat.h>
#include <signal.h>//<csignal>//sig_atomic_t,signal, SIG.+,
#include <stdio.h>//<cstdio>//fopen/fclose,perror,fread/fwrite,size_t,NULL,printf,
#include <stdlib.h>//<cstdlib>//abort,calloc,free,
#include <string.h>//<cstring>//memset,strlen,
#include <time.h>//<ctime>//time_t,/*define and select a strategy file type here*/
#define FORMAT_UNKNOWN (0)
#define FORMAT_XML (1)
#define FORMAT_JSON (2)
#define FORMAT_INI (3)
#if 0
#   define STRATEGY_FORMAT FORMAT_XML
#elif 0
#   define STRATEGY_FORMAT FORMAT_JSON
#elif 1
#   define STRATEGY_FORMAT FORMAT_INI
#else
#   define STRATEGY_FORMAT FORMAT_UNKNOWN
#endif
/*auto concate for strategy file path*/
#define concate(x, y) x y//
#if STRATEGY_FORMAT == FORMAT_XML
#   define STRATEGY_SUFFIX ".xml"
#elif STRATEGY_FORMAT == FORMAT_JSON
#   define STRATEGY_SUFFIX ".json"
#elif STRATEGY_FORMAT == FORMAT_INI
#   define STRATEGY_SUFFIX ".ini"
#else//FORMAT_UNKNOWN
#   define STRATEGY_SUFFIX ".txt"
#endif
#define STRATEGY_FILE concate("/tmp/strategy", STRATEGY_SUFFIX)
#define STRATEGY_FILE_MAX_SIZE _IO_BUFSIZ
#define thread_failed(s, msg) \
do{ \errno = s, perror(msg); \abort(); \
}while(0)/*to stop the update-thread and main-thread:by user signal SIGINTnotice:to keep data consistence of thread access, don't optmize to cache    */
static volatile int stop = 0;
static void handle_exception(sig_atomic_t sig){signal(sig, SIG_IGN);stop = 1;
}
/*exception protection:shadow other signals except SIGINT(SIGKILL,SIGSTOP is special)*/
static void shadow_exception(){sig_atomic_t sig;for(sig = 1; sig <= 64; sig++){if(sig == SIGINT)continue;if(sig > 31 && sig < 34)continue;signal(sig, SIG_IGN);}
}/*to load and update strategy file:by the latest update time(content modification or fresh time only)*/
static time_t latestUpdate;
/*to minimized lock conflict:split reader and writer*/
static pthread_rwlock_t rwLock;
/*to keep integrity of strategy file data:by lock and swap pointer(minimized lock conflict)*/
static char *strategyContent/* = NULL */;
static char *strategyContentBak/* = NULL */;
/*to make more concurrency of reader, copy a strategy self, use it without lock conflict*/
static char *strategyContentCopy/* = NULL*/;//improve performance(for reader)
/*@brief swap for any type of pointer@parama: pointer1(the length is the same as size_t)b: pointer2(the length is the same as size_t)@problem solved(user may be interested in it)convert failed for rvalue(expression) can't be write:(size_t)strategyContent ^= (size_t)strategyContentBakso, write as follows:get address => convert address type => dereference(access momory forcely)*(size_t*)&strategyContent    ^= *(size_t*)&strategyContentBak; 
*/
#define swap_pointer(a, b) _swap_pointer((size_t*)&a, (size_t*)&b)//wrapper for use it easily!!!
static void _swap_pointer(register size_t *a, register size_t *b){*a ^= *b;*b ^= *a;*a ^= *b;
}
/*swap strategy file buffer*/
static void swap(){int s;if( (s = pthread_rwlock_wrlock(&rwLock)) )thread_failed(s, "pthread_rwlock_wrlock");
#ifndef NDEBUG/*for view of debug*/printf("\nuser update the strategy file now!\n");        
#endifswap_pointer(strategyContent, strategyContentBak);pthread_rwlock_unlock(&rwLock);
}
/*reload and update strategy file*/
static void reload(time_t currentUpdate){FILE *fp = NULL;latestUpdate = currentUpdate;if( (fp = fopen(STRATEGY_FILE, "r")) ){memset(strategyContentBak, 0, sizeof(char) * STRATEGY_FILE_MAX_SIZE);//keep clean for textfread(strategyContentBak, sizeof(char), STRATEGY_FILE_MAX_SIZE, fp);fclose(fp), fp = NULL;swap();}else{perror("fopen");abort();}
}
/*update-thread:check if file is freshed, then reloadexcecption protection:after remove strategy file  */
static void *update(void* args){struct stat fbuf;time_t currentUpdate = 0;while(!stop){if(-1 == stat(STRATEGY_FILE, &fbuf) ){perror("stat");//to get position, __FILE__,__FUNCTION__,__LINE__ may be usedgoto __next_round;//avoid fresh the screen frequently}currentUpdate = fbuf.st_mtime;if(currentUpdate > latestUpdate)reload(currentUpdate);
__next_round:sleep(4);}
#ifndef NDEBUG/*for view of debug*/printf("\nupdate-thread exit now!\n");
#endifpthread_exit(NULL);
}/*allocate and deallocate for system resource*/ 
static char hasInit/* = 0*/;
static void init(){int s;pthread_t tid;signal(SIGINT, handle_exception);if( (s = pthread_create(&tid, NULL, update, NULL)))thread_failed(s, "pthread_create");if( (s = pthread_rwlock_init(&rwLock, NULL)) )thread_failed(s, "pthread_rwlock_init");if( !(strategyContent = calloc(sizeof(char), STRATEGY_FILE_MAX_SIZE) ) ){perror("calloc");abort();}if( !(strategyContentBak = calloc(sizeof(char), STRATEGY_FILE_MAX_SIZE) ) ){perror("calloc");abort();}if( !(strategyContentCopy = calloc(sizeof(char), STRATEGY_FILE_MAX_SIZE) ) ){perror("calloc");abort();}hasInit = 1;
}
static void destroy(){if(hasInit){pthread_rwlock_destroy(&rwLock);free(strategyContent), strategyContent = NULL;free(strategyContentBak), strategyContentBak = NULL;free(strategyContentCopy), strategyContentCopy = NULL;}
}/*compatible for multi-thread shared read:read and use the strategy file*/
static int readCount/* = 0 */;
static void read_use(){int s;if( (s = pthread_rwlock_rdlock(&rwLock)) )thread_failed(s, "pthread_rwlock_rdlock");memcpy(strategyContentCopy, strategyContent, STRATEGY_FILE_MAX_SIZE * sizeof(char));pthread_rwlock_unlock(&rwLock);printf("\n>>>%dth read strategyContent:\n", ++readCount);//CLIfwrite(strategyContent, sizeof(char), strlen(strategyContent), stdout);
}/*prepare strategy file for test*/
static void prepare(){
#if STRATEGY_FORMAT == FORMAT_XML//.xmlsystem("echo \"<?xml version=\\\"1.0\\\" encoding=\\\"utf-8\\\"?>\"   >" STRATEGY_FILE ";""echo \"<root>\"                         >>" STRATEGY_FILE ";""echo \"\t<strategy>\"                   >>" STRATEGY_FILE ";""echo \"\t\t<person>\"                   >>" STRATEGY_FILE ";""echo \"\t\t\t<name>john</name>\"        >>" STRATEGY_FILE ";""echo \"\t\t\t<age>18</age>\"            >>" STRATEGY_FILE ";""echo \"\t\t\t<weight>61.38kg</weight>\" >>" STRATEGY_FILE ";""echo \"\t\t\t<married>false</married>\" >>" STRATEGY_FILE ";""echo \"\t\t</person>\"                  >>" STRATEGY_FILE ";""echo \"\t</strategy>\"                  >>" STRATEGY_FILE ";""echo \"</root>\"                        >>" STRATEGY_FILE );
#elif STRATEGY_FORMAT == FORMAT_JSON//.jsonsystem("echo \"{\"                                      >" STRATEGY_FILE ";""echo \"\t\\\"strategy\\\":{\"                  >>" STRATEGY_FILE ";""echo \"\t\t\\\"person\\\":{\"                  >>" STRATEGY_FILE ";""echo \"\t\t\t\\\"name\\\":\\\"john\\\",\"      >>" STRATEGY_FILE ";""echo \"\t\t\t\\\"age\\\":\\\"18\\\",\"         >>" STRATEGY_FILE ";""echo \"\t\t\t\\\"weight\\\":\\\"61.38kg\\\",\" >>" STRATEGY_FILE ";""echo \"\t\t\t\\\"married\\\":\\\"false\\\"\"   >>" STRATEGY_FILE ";""echo \"\t\t}\"                                 >>" STRATEGY_FILE ";""echo \"\t}\"                                   >>" STRATEGY_FILE ";""echo \"}\"                                     >>" STRATEGY_FILE);
#elif STRATEGY_FORMAT == FORMAT_INI//.inisystem("echo \"[strategy]\"           >" STRATEGY_FILE ";""echo \"id     =1234567890#\" >>" STRATEGY_FILE ";""echo \"name   =john#\"       >>" STRATEGY_FILE ";""echo \"age    =18#\"         >>" STRATEGY_FILE ";""echo \"weight =61.38kg#\"    >>" STRATEGY_FILE ";""echo \"married=false#\"      >>" STRATEGY_FILE);
#else//.txtsystem("touch " STRATEGY_FILE);
#endif
}/*main frame here*/
int main(){shadow_exception();prepare();init();while(!stop){sleep(2);read_use();}
#ifndef NDEBUG/*for view of debug*/printf("\nmain-thread waitting to collect resource ... \n");sleep(10);
#endifdestroy();return 0;
}

小結：

1）可以使用異步信號通知的方式，保持訪問標志變量的一致性，將更新線程與主線程停下來

2）通過最后一次修改時間與上一次做比對，來確定配置文件是否有更新，在同步更新時要注意清理上一次配置文件的內容并保持本次配置文件的完整性

3）讀時共享，寫時互斥(w-w,w-r), 區分writer與reader, 讓需要配置的多線程最大程度并發，同時將需要同步競爭的數據拷貝來進一步提高reader并發量

4）更新配置文件一般是比較輕松的任務，可以最大限度讓出CPU給系統其它任務使用

提示：實際開發當中配置文件會比較復雜，與業務邏輯強相關，常見的有XML, JSON, INI, TXT需要加載后解析到指定的內存結構，同步分給相應的任務使用