/* Only register the performance-critical methods */
static JNINativeMethod methods[] = {
{"currentTimeMillis", "()J", (void *)&JVM_CurrentTimeMillis},
{"nanoTime", "()J", (void *)&JVM_NanoTime},
{"arraycopy", "(" OBJ "I" OBJ "II)V", (void *)&JVM_ArrayCopy},
};
方法的實現應該在JVM部分,路徑openjdk-7-fcs-src-b147\hotspot\src\share,不同的操作系統實現不壹樣,應該是在對應的操作系統的包下,我在windows目錄下找到了納秒的實現
jlong os::javaTimeNanos() {
if (!has_performance_count) {
return javaTimeMillis() * NANOS_PER_MILLISEC; // the best we can do.
} else {
LARGE_INTEGER current_count;
QueryPerformanceCounter(¤t_count);
double current = as_long(current_count);
double freq = performance_frequency;
jlong time = (jlong)((current/freq) * NANOS_PER_SEC);
return time;
}
}
看到了這個比較有趣的東西。。。
the best we can do.
再詳細的懶得找了。我這沒環境,沒IDE,有環境的話,用IDE幾下子就找到了。最終結論:performance_frequency,QueryPerformanceCounter;
這個就是windows下的C API函數。至於這個函數,可以去google