synchronized 处发生了什么

问题
1.为何 map.clear(); 时的输出的毫秒数不连续？
2.在 synchronized (map) 处发生了什么？


代码

public class Test {
	static transient long   currentMs;
	static Map map = new HashMap();
	
	public static void main(String[] args) {
		{
			long start = System.currentTimeMillis();
			int  spans = 1000;
			Map m = new HashMap();
			int count=0;
			while(System.currentTimeMillis() - start < spans) {
				Integer i = new Integer(count); 
				m.put(i,i);
		    	count++;
			}
			long total = System.currentTimeMillis()-start;
			System.out.println("|| SimpleAdd || "+(count/total)+" ||");
		}
		{
			long start = System.currentTimeMillis();
			int  spans = 1000;
			int count=0;
			while(System.currentTimeMillis() - start < spans) {
				make(count);
		    	count++;
			}
			long total = System.currentTimeMillis()-start;
			System.out.println("|| MethodAdd || "+(count/total)+" ||");
		}
	}

	public static void make(int c) {
		synchronized (map) {
			final long nowMs = System.currentTimeMillis();
			if(nowMs >currentMs){
				System.out.println("map.clear()="+nowMs+", map.size()="+map.size());
				map.clear();
				currentMs=nowMs;
			}
			Integer i = new Integer(c);
			map.put(i, i);
		}
	}
}

输出
|| A9ICMaker.make():SingleThread || 1273 ||
clear=1294900633538,count=0
clear=1294900633553,count=7533
clear=1294900633569,count=71077
clear=1294900633584,count=44649
clear=1294900633600,count=60189
clear=1294900633616,count=77277
clear=1294900633631,count=72338
clear=1294900633647,count=60071
clear=1294900633663,count=79539
clear=1294900633678,count=75039
clear=1294900633694,count=55106
clear=1294900633709,count=85094
clear=1294900633725,count=78181
clear=1294900633741,count=57666
clear=1294900633756,count=93585
clear=1294900633772,count=16451
clear=1294900633788,count=88381
clear=1294900633803,count=32323
clear=1294900633819,count=72507
clear=1294900633834,count=57766
clear=1294900633850,count=56261
clear=1294900633866,count=95639
clear=1294900633881,count=15986
clear=1294900633897,count=88842
clear=1294900633913,count=23015
clear=1294900633928,count=81801
clear=1294900633944,count=39540
clear=1294900633959,count=65284
clear=1294900633975,count=71901
clear=1294900633991,count=65975
clear=1294900634006,count=71771
clear=1294900634022,count=60254
clear=1294900634038,count=55864
clear=1294900634053,count=93507
clear=1294900634069,count=19888
clear=1294900634084,count=84916
clear=1294900634100,count=33104
clear=1294900634116,count=71716
clear=1294900634131,count=57352
clear=1294900634147,count=56235
clear=1294900634163,count=96052
clear=1294900634178,count=15489
clear=1294900634194,count=85669
clear=1294900634209,count=93119
clear=1294900634225,count=84102
clear=1294900634241,count=64900
clear=1294900634256,count=75998
clear=1294900634272,count=50408
clear=1294900634288,count=54407
clear=1294900634303,count=92945
clear=1294900634319,count=85162
clear=1294900634334,count=66641
clear=1294900634381,count=69714
clear=1294900634397,count=87046
clear=1294900634413,count=87289
clear=1294900634428,count=83505
clear=1294900634444,count=70047
clear=1294900634459,count=58651
clear=1294900634475,count=85536
clear=1294900634491,count=89269
clear=1294900634506,count=76467
clear=1294900634522,count=55252
|| A9ICMaker.make():SingleThread || 4101 ||