Java多线程与CPU核数在资源占用上的关系
环境：Linux Redhat 5.4 32位，CPU8核
Java代码如下：
class Loop {
????????public static void main(String[] args) {
????????????????for(int i=0;i<7;i++)
????????????????????????new Thread(new Runnable(){
????????????????????????public void run() {
????????????????????????????????while(true);
????????????????????????}
????????????????????????}).start();
????????????????while(true);
????????}
}
编译后启动，输入top命令可看到：
Tasks: 215 total,?? 1 running, 214 sleeping,?? 0 stopped,?? 0 zombie
Cpu(s):100.0%us,??0.0%sy,??0.0%ni,??0.0%id,??0.0%wa,??0.0%hi,??0.0%si,??0.0%st
Mem:??16580348k total,??7986304k used,??8594044k free,?? 577356k buffers
Swap: 16777208k total,????????0k used, 16777208k free,??5988556k cached
??PID USER??????PR??NI??VIRT??RES??SHR S %CPU %MEM????TIME+??COMMAND
18833 flow??????18?? 0 1176m??18m 7620 S?798.5??0.1?? 2:11.62 java
按1后可显示每个CPU核的情况：
top - 15:02:39 up 15 days,??3:40,??4 users,??load average: 7.17, 2.92, 1.24
Tasks: 215 total,?? 1 running, 214 sleeping,?? 0 stopped,?? 0 zombie
Cpu0??:100.0%us,??0.0%sy,??0.0%ni,??0.0%id,??0.0%wa,??0.0%hi,??0.0%si,??0.0%st
Cpu1??:100.0%us,??0.0%sy,??0.0%ni,??0.0%id,??0.0%wa,??0.0%hi,??0.0%si,??0.0%st
Cpu2??:?99.7%us,??0.3%sy,??0.0%ni,??0.0%id,??0.0%wa,??0.0%hi,??0.0%si,??0.0%st
Cpu3??:?99.3%us,??0.0%sy,??0.0%ni,??0.0%id,??0.0%wa,??0.3%hi,??0.3%si,??0.0%st
Cpu4??:100.0%us,??0.0%sy,??0.0%ni,??0.0%id,??0.0%wa,??0.0%hi,??0.0%si,??0.0%st
Cpu5??:100.0%us,??0.0%sy,??0.0%ni,??0.0%id,??0.0%wa,??0.0%hi,??0.0%si,??0.0%st
Cpu6??:100.0%us,??0.0%sy,??0.0%ni,??0.0%id,??0.0%wa,??0.0%hi,??0.0%si,??0.0%st
Cpu7??:100.0%us,??0.0%sy,??0.0%ni,??0.0%id,??0.0%wa,??0.0%hi,??0.0%si,??0.0%st
Mem:??16580348k total,??7986616k used,??8593732k free,?? 577396k buffers
Swap: 16777208k total,????????0k used, 16777208k free,??5989628k cached
??PID USER??????PR??NI??VIRT??RES??SHR S %CPU %MEM????TIME+??COMMAND
18833 flow??????18?? 0 1176m??18m 7620 S?793.3??0.1?? 9:44.87 java
由此可见8个线程占用了8个CPU核的资源，资源达到100%。
我们修改下代码，改成：
class Loop {
????????public static void main(String[] args) {
????????????????while(true);
????????}
同样按top命令，可看到就只有1个CPU达到100%（注某一时刻可能是核1，过会可能是核2），其他几个CPU核均很小。
由此可见，1个线程只会使用1个cpu核资源，多线程可充分利用物理资源。
看过Mina的童鞋应该知道，Mina的推荐的IoProcessor线程池IO线程数为核数+1就是这个原因。
