在做NtyTcp 的时候,有一些,就想用c来实现一套try-catch异常处理子系统。
不讨论C语言本身为什么不加try-catch,每个开发的朋友对于这个问题,都能说出一大堆的理由。
其实我也是不太喜欢强行在c中加入一个try-catch。就像把try-catch的原理跟自己的体会写出来。
首先我们来看看,try-catch的使用情景。
try {
throw Excep;
} catch (Excep) {
} finally {
}
try{ } 块是可能有异常的抛出的地方。throw Excep
catch (Excep) { } 是 捕获相应抛出异常的地方。
finally { } 是不论什么情形下,都是需要执行的代码块。
如果实现一套如此机制,有何实现的基础依赖。那就是setjmp与longjmp
讲到setjmp与longjmp,也是更说明一下
#include <setjmp.h>
#include <stdio.h>
jmp_buf env;
int count = 0;
void sub_func(int idx) {
printf("sub_func --> idx:%d\n", idx);
longjmp(env, idx);
}
int main(int argc, char *argv[]) {
int idx = 0;
if ((count = setjmp(env)) == 0) {
printf("count:%d\n", count);
sub_func(++idx);
} else if (count == 1) {
printf("count:%d\n", count);
} {
printf("other count\n");
}
return 0;
}
先来定义个
全局的jmp_buf env; 用来保存跳转的上下文。
int count = 0; 用来保存跳转返回值的。有点绕口,就是记录setjmp返回值的。
看到这里也许对setjmp与longjmp有点理解。再换个马甲,相信更有体会。
#include <setjmp.h>
#include <stdio.h>
jmp_buf env;
int count = 0;
#define Try if ((count = setjmp(env)) == 0)
#define Catch(e) else if (count == (e))
#define Finally ;
#define Throw(idx) longjmp(env, (idx))
void sub_func(int idx) {
printf("sub_func --> idx:%d\n", idx);
Throw(idx);
}
int main(int argc, char *argv[]) {
int idx = 0;
Try {
printf("count:%d\n", count);
sub_func(++idx);
} Catch(1) {
printf("count:%d\n", count);
} Finally {
printf("other count\n");
}
return 0;
}
try-catch就已经初具雏形了。这样只是基本实现,还有三个问题没有解决。
如何保证线程安全。
如何解决try-catch 嵌套。
如何避免,在不加try的代码块直接Throw。
如何保证线程安全。
使用线程的私有数据 pthread_key_t ,每一个线程都有一个try-catch的上下文环境。
如何解决try-catch嵌套的问题
使用一个栈式数据结构,每次try的时候压栈,每次throw的时候 出栈。
如何避免,在不加try的代码块直接Throw,
这个问题就比较好理解。既然每次try需要压栈,如果不加try,所以栈里面没有数据。在Throw之前先查看栈里面有没有数据。
那现在问题又来了,在pthread_key_t 与 链式栈如何结合? 先看如下结构体,也许会有新的认识,结构体里面有一个prev的域。
这样就能跟pthread_key_t 来结合,每次讲结构体指针保存在pthread_key_t中,获取完之后,拿到prev的值。
typedef struct _ntyExceptionFrame {
jmp_buf env;
int line;
const char *func;
const char *file;
ntyException *exception;
struct _ntyExceptionFrame *prev;
char message[EXCEPTIN_MESSAGE_LENGTH+1];
} ntyExceptionFrame;
下面把整个实现代码都贴出来,大家也可以去我的github上面star,fork
/*
* author : wangbojing
* email : 1989wangbojing@163.com
* github : https://github.com/wangbojing
*/
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <stdarg.h>
#include <pthread.h>
#include <setjmp.h>
#define ntyThreadData pthread_key_t
#define ntyThreadDataSet(key, value) pthread_setspecific((key), (value))
#define ntyThreadDataGet(key) pthread_getspecific((key))
#define ntyThreadDataCreate(key) pthread_key_create(&(key), NULL)
#define EXCEPTIN_MESSAGE_LENGTH 512
typedef struct _ntyException {
const char *name;
} ntyException;
ntyException SQLException = {"SQLException"};
ntyException TimeoutException = {"TimeoutException"};
ntyThreadData ExceptionStack;
typedef struct _ntyExceptionFrame {
jmp_buf env;
int line;
const char *func;
const char *file;
ntyException *exception;
struct _ntyExceptionFrame *prev;
char message[EXCEPTIN_MESSAGE_LENGTH+1];
} ntyExceptionFrame;
#define ntyExceptionPopStack \
ntyThreadDataSet(ExceptionStack, ((ntyExceptionFrame*)ntyThreadDataGet(ExceptionStack))->prev)
#define ReThrow ntyExceptionThrow(frame.exception, frame.func, frame.file, frame.line, NULL)
#define Throw(e, cause, ...) ntyExceptionThrow(&(e), __func__, __FILE__, __LINE__, cause, ##__VA_ARGS__, NULL)
enum {
ExceptionEntered = 0,
ExceptionThrown,
ExceptionHandled,
ExceptionFinalized
};
#define Try do { \
volatile int Exception_flag; \
ntyExceptionFrame frame; \
frame.message[0] = 0; \
frame.prev = (ntyExceptionFrame*)ntyThreadDataGet(ExceptionStack); \
ntyThreadDataSet(ExceptionStack, &frame); \
Exception_flag = setjmp(frame.env); \
if (Exception_flag == ExceptionEntered) {
#define Catch(e) \
if (Exception_flag == ExceptionEntered) ntyExceptionPopStack; \
} else if (frame.exception == &(e)) { \
Exception_flag = ExceptionHandled;
#define Finally \
if (Exception_flag == ExceptionEntered) ntyExceptionPopStack; \
} { \
if (Exception_flag == ExceptionEntered) \
Exception_flag = ExceptionFinalized;
#define EndTry \
if (Exception_flag == ExceptionEntered) ntyExceptionPopStack; \
} if (Exception_flag == ExceptionThrown) ReThrow; \
} while (0)
static pthread_once_t once_control = PTHREAD_ONCE_INIT;
static void init_once(void) {
ntyThreadDataCreate(ExceptionStack);
}
void ntyExceptionInit(void) {
pthread_once(&once_control, init_once);
}
void ntyExceptionThrow(ntyException *excep, const char *func, const char *file, int line, const char *cause, ...) {
va_list ap;
ntyExceptionFrame *frame = (ntyExceptionFrame*)ntyThreadDataGet(ExceptionStack);
if (frame) {
frame->exception = excep;
frame->func = func;
frame->file = file;
frame->line = line;
if (cause) {
va_start(ap, cause);
vsnprintf(frame->message, EXCEPTIN_MESSAGE_LENGTH, cause, ap);
va_end(ap);
}
ntyExceptionPopStack;
longjmp(frame->env, ExceptionThrown);
} else if (cause) {
char message[EXCEPTIN_MESSAGE_LENGTH+1];
va_start(ap, cause);
vsnprintf(message, EXCEPTIN_MESSAGE_LENGTH, cause, ap);
va_end(ap);
printf("%s: %s\n raised in %s at %s:%d\n", excep->name, message, func ? func : "?", file ? file : "?", line);
} else {
printf("%s: %p\n raised in %s at %s:%d\n", excep->name, excep, func ? func : "?", file ? file : "?", line);
}
}
/* ** **** ******** **************** debug **************** ******** **** ** */
ntyException A = {"AException"};
ntyException B = {"BException"};
ntyException C = {"CException"};
ntyException D = {"DException"};
void *thread(void *args) {
pthread_t selfid = pthread_self();
Try {
Throw(A, "A");
} Catch (A) {
printf("catch A : %ld\n", selfid);
} EndTry;
Try {
Throw(B, "B");
} Catch (B) {
printf("catch B : %ld\n", selfid);
} EndTry;
Try {
Throw(C, "C");
} Catch (C) {
printf("catch C : %ld\n", selfid);
} EndTry;
Try {
Throw(D, "D");
} Catch (D) {
printf("catch D : %ld\n", selfid);
} EndTry;
Try {
Throw(A, "A Again");
Throw(B, "B Again");
Throw(C, "C Again");
Throw(D, "D Again");
} Catch (A) {
printf("catch A again : %ld\n", selfid);
} Catch (B) {
printf("catch B again : %ld\n", selfid);
} Catch (C) {
printf("catch C again : %ld\n", selfid);
} Catch (D) {
printf("catch B again : %ld\n", selfid);
} EndTry;
}
#define THREADS 50
int main(void) {
ntyExceptionInit();
Throw(D, NULL);
Throw(C, "null C");
printf("\n\n=> Test1: Try-Catch\n");
Try {
Try {
Throw(B, "recall B");
} Catch (B) {
printf("recall B \n");
} EndTry;
Throw(A, NULL);
} Catch(A) {
printf("\tResult: Ok\n");
} EndTry;
printf("=> Test1: Ok\n\n");
printf("=> Test2: Test Thread-safeness\n");
#if 1
int i = 0;
pthread_t threads[THREADS];
for (i = 0;i < THREADS;i ++) {
pthread_create(&threads[i], NULL, thread, NULL);
}
for (i = 0;i < THREADS;i ++) {
pthread_join(threads[i], NULL);
}
#endif
printf("=> Test2: Ok\n\n");
}
转载于:https://blog.51cto.com/wangbojing/2120520