最近发现项目中的日志用得不大规范，于是准备做些改造，在我们项目中用的是 slf4j1.5.10 的版本，顺便看了下 slf4j 的源码，看到 LoggerFactory 初始化的逻辑如下
public static ILoggerFactory getILoggerFactory() {
if (INITIALIZATION_STATE == UNINITIALIZED) {
INITIALIZATION_STATE = ONGOING_INITILIZATION;
performInitialization();
}
switch (INITIALIZATION_STATE) {
case SUCCESSFUL_INITILIZATION:
return getSingleton().getLoggerFactory();
case FAILED_INITILIZATION:
throw new IllegalStateException(UNSUCCESSFUL_INIT_MSG);
case ONGOING_INITILIZATION:
// support re-entrant behavior.
// See also http://bugzilla.slf4j.org/show_bug.cgi?id=106
return TEMP_FACTORY;
}
throw new IllegalStateException("Unreachable code");
}
有发现什么问题吗？再看看 INITIALIZATION_STATE 这个变量是怎么声明的，如下
static int INITIALIZATION_STATE = UNINITIALIZED;
现在很明确了，如果在多线程环境下，多个线程调用 LoggerFactory.getLogger() 方法的时候初始化会出现问题，这简直有点颠覆世界观，说好的大神代码呢？怀着极度怀疑自己的心情翻看了最新的 slf4j1.7.21 代码，看到初始化逻辑如下:
public static ILoggerFactory getILoggerFactory() {
if (INITIALIZATION_STATE == UNINITIALIZED) {
synchronized (LoggerFactory.class) {
if (INITIALIZATION_STATE == UNINITIALIZED) {
INITIALIZATION_STATE = ONGOING_INITIALIZATION;
performInitialization();
}
}
}
switch (INITIALIZATION_STATE) {
case SUCCESSFUL_INITIALIZATION:
return StaticLoggerBinder.getSingleton().getLoggerFactory();
case NOP_FALLBACK_INITIALIZATION:
return NOP_FALLBACK_FACTORY;
case FAILED_INITIALIZATION:
throw new IllegalStateException(UNSUCCESSFUL_INIT_MSG);
case ONGOING_INITIALIZATION:
// support re-entrant behavior.
// See also http://jira.qos.ch/browse/SLF4J-97
return SUBST_FACTORY;
}
throw new IllegalStateException("Unreachable code");
}
再看看 INITIALIZATION_STATE 变量的声明
static volatile int INITIALIZATION_STATE = UNINITIALIZED;
顿时泪流满面，这才像传说中的大神代码啊
