典型的日志实现步骤:
1、声明几种日志等级(可以是enum类型,或者几个宏定义)
libevent的日志等级定义在event.h中,如下(个人觉得放在log的头文件岂不是更好?):
/** @name Log severities */ /**@{*/ #define EVENT_LOG_DEBUG 0 #define EVENT_LOG_MSG 1 #define EVENT_LOG_WARN 2 #define EVENT_LOG_ERR 3 /**@}*/ /* Obsolete names: these are deprecated, but older programs might use them. * They violate the reserved-identifier namespace. */ #define _EVENT_LOG_DEBUG EVENT_LOG_DEBUG #define _EVENT_LOG_MSG EVENT_LOG_MSG #define _EVENT_LOG_WARN EVENT_LOG_WARN #define _EVENT_LOG_ERR EVENT_LOG_ERR
可以看到有四种等级:调试、消息、警告、错误。
2、实现日志打印函数。
可以为每个日志等级实现各自的打印函数,也可以统一在一个函数中。一个常用的模板:
event_log(int severity, const char *msg)
{
if (log_fn)//是否设置了自定义的日志打印函数,是的话就调用用户自定义的日志打印函数
log_fn(severity, msg);
else {
const char *severity_str;
switch (severity) {//判断等级
case _EVENT_LOG_DEBUG:
severity_str = "debug";
break;
case _EVENT_LOG_MSG:
severity_str = "msg";
break;
case _EVENT_LOG_WARN:
severity_str = "warn";
break;
case _EVENT_LOG_ERR:
severity_str = "err";
break;
default:
severity_str = "???";
break;
}
(void)fprintf(stderr, "[%s] %s\n", severity_str, msg);
}
}
3、定义一个全局回调函数指针,实现一个可以让用户设置回调函数的接口。用户没有调用该接口设置自定义的日志打印函数的话,就用第二步的默认日志打印函数。
static event_log_cb log_fn = NULL;
event_log_cb是一种函数指针类型,定义在event.h : typedef void (*event_log_cb)(int severity, const char *msg);
设置回调函数的接口很简单,把全局回调函数指针赋值为我们自己定义的函数即可:
void event_set_log_callback(event_log_cb cb)
{
log_fn = cb;
}
头文件log-internal.h:
#ifndef _LOG_H_ #define _LOG_H_ #include "event2/util.h" #ifdef __GNUC__ #define EV_CHECK_FMT(a,b) __attribute__((format(printf, a, b))) #define EV_NORETURN __attribute__((noreturn)) #else #define EV_CHECK_FMT(a,b) #define EV_NORETURN #endif #define _EVENT_ERR_ABORT ((int)0xdeaddead) void event_err(int eval, const char *fmt, ...) EV_CHECK_FMT(2,3) EV_NORETURN; void event_warn(const char *fmt, ...) EV_CHECK_FMT(1,2); void event_sock_err(int eval, evutil_socket_t sock, const char *fmt, ...) EV_CHECK_FMT(3,4) EV_NORETURN; void event_sock_warn(evutil_socket_t sock, const char *fmt, ...) EV_CHECK_FMT(2,3); void event_errx(int eval, const char *fmt, ...) EV_CHECK_FMT(2,3) EV_NORETURN; void event_warnx(const char *fmt, ...) EV_CHECK_FMT(1,2); void event_msgx(const char *fmt, ...) EV_CHECK_FMT(1,2); void _event_debugx(const char *fmt, ...) EV_CHECK_FMT(1,2); #ifdef USE_DEBUG #define event_debug(x) _event_debugx x #else #define event_debug(x) do {;} while (0) #endif #undef EV_CHECK_FMT #endifevent_xxxx是最后封装好的日志打印函数,内部调用流程如下(以event_errx为例,其他一样)
event_errx->_warn_helper->fprintf
源文件log.c
#include "event2/event-config.h" #ifdef WIN32 #include <winsock2.h> #define WIN32_LEAN_AND_MEAN #include <windows.h> #undef WIN32_LEAN_AND_MEAN #endif #include <sys/types.h> #include <stdio.h> #include <stdlib.h> #include <stdarg.h> #include <string.h> #include <errno.h> #include "event2/event.h" #include "event2/util.h" #include "log-internal.h" static void _warn_helper(int severity, const char *errstr, const char *fmt, va_list ap); static void event_log(int severity, const char *msg); static void event_exit(int errcode) EV_NORETURN; static event_fatal_cb fatal_fn = NULL; void event_set_fatal_callback(event_fatal_cb cb) { fatal_fn = cb; } static void event_exit(int errcode) { if (fatal_fn) { fatal_fn(errcode); exit(errcode); /* should never be reached */ } else if (errcode == _EVENT_ERR_ABORT) abort(); else exit(errcode); } void event_err(int eval, const char *fmt, ...) { va_list ap; va_start(ap, fmt); _warn_helper(_EVENT_LOG_ERR, strerror(errno), fmt, ap); va_end(ap); event_exit(eval); } void event_warn(const char *fmt, ...) { va_list ap; va_start(ap, fmt); _warn_helper(_EVENT_LOG_WARN, strerror(errno), fmt, ap); va_end(ap); } void event_sock_err(int eval, evutil_socket_t sock, const char *fmt, ...) { va_list ap; int err = evutil_socket_geterror(sock); va_start(ap, fmt); _warn_helper(_EVENT_LOG_ERR, evutil_socket_error_to_string(err), fmt, ap); va_end(ap); event_exit(eval); } void event_sock_warn(evutil_socket_t sock, const char *fmt, ...) { va_list ap; int err = evutil_socket_geterror(sock); va_start(ap, fmt); _warn_helper(_EVENT_LOG_WARN, evutil_socket_error_to_string(err), fmt, ap); va_end(ap); } void event_errx(int eval, const char *fmt, ...) { va_list ap; va_start(ap, fmt); _warn_helper(_EVENT_LOG_ERR, NULL, fmt, ap); va_end(ap); event_exit(eval); } void event_warnx(const char *fmt, ...) { va_list ap; va_start(ap, fmt); _warn_helper(_EVENT_LOG_WARN, NULL, fmt, ap); va_end(ap); } void event_msgx(const char *fmt, ...) { va_list ap; va_start(ap, fmt); _warn_helper(_EVENT_LOG_MSG, NULL, fmt, ap); va_end(ap); } void _event_debugx(const char *fmt, ...) { va_list ap; va_start(ap, fmt); _warn_helper(_EVENT_LOG_DEBUG, NULL, fmt, ap); va_end(ap); } static void _warn_helper(int severity, const char *errstr, const char *fmt, va_list ap) { char buf[1024]; size_t len; if (fmt != NULL) evutil_vsnprintf(buf, sizeof(buf), fmt, ap); else buf[0] = '\0'; if (errstr) { len = strlen(buf); if (len < sizeof(buf) - 3) { evutil_snprintf(buf + len, sizeof(buf) - len, ": %s", errstr); } } event_log(severity, buf); } static event_log_cb log_fn = NULL; void event_set_log_callback(event_log_cb cb) { log_fn = cb; } static void event_log(int severity, const char *msg) { if (log_fn) log_fn(severity, msg); else { const char *severity_str; switch (severity) { case _EVENT_LOG_DEBUG: severity_str = "debug"; break; case _EVENT_LOG_MSG: severity_str = "msg"; break; case _EVENT_LOG_WARN: severity_str = "warn"; break; case _EVENT_LOG_ERR: severity_str = "err"; break; default: severity_str = "???"; break; } (void)fprintf(stderr, "[%s] %s\n", severity_str, msg); } }