「翻譯」一篇redis文章引發的翻譯——JVM能支持多少線程？
昨天看了一篇關於redis 的文章https://www.cnblogs.com/fanwencong/p/5782860.html
作者說他模擬了100萬線程的並發，我對這個有一些懷疑，看了評論也有很多質疑的聲音。當然我這篇不是要批評作者對線程的模擬，事實上作者寫的對redis的使用是很不錯的，我們本篇主要針對個人電腦上的JVM最多能支持多少個線程。以下是StackOverflow上的一個提問，我簡單的翻譯了一下。
StackOverflow原回答請點我
Eddie 的回答
This depends on the CPU you‘re using, on the OS, on what other processes are doing, on what Java release you‘re using, and other factors. I‘ve seen a WINDOWS
譯：這取決於你使用的CPU、操作系統、取決於其他進程在處理什麽事情、你使用的Java版本和其他因素。我曾經見過一個WINDOWS 服務器，它上面有超過6500個線程。當然大多數線程是空閑的。一旦電腦上達到6500個線程（在Java中），整個機器開始出現問題並且變得不穩定。我的經驗是無論計算機本身能夠維持多少線程，Java（最近版本的）都能吃得下，並且不出問題。當然你需要足夠的RAM並且你必須用足夠的內存來啟動Java來滿足這麽多線程的需要，並且需要有一個棧來存儲線程。任何使用現代CPU的計算機（最近兩代的AMD或Intel）和1-2G的內存（取決於操作系統）就可以支持JVM創建上千個線程。如果你需要比這個回答更具體的答案，最好的選擇是看一下相關的文檔。
Charlie Martin 的回答
Um, lots.
There are several parameters here. The specific VM, plus there are usually run-time parameters on the VM as well. That‘s somewhat driven by the operating system: what support does the underlying OS have for threads and what limitations does it put on them? If the VM actually uses OS-level threads at all, the good old red thread/green thread thing.
What "support" means is another question. If you write a Java program that is just something like
class DieLikeADog {
public static void main(String[] argv){
for(;;){
new Thread(new SomeRunaable).start();
}
}
}(and don‘t complain about little syntax details, I‘m on my first cup of coffee) then you should certainly expect to get hundreds or thousands of threads running. But creating a Thread is relatively expensive, and scheduler overhead can get intense; it‘s unclear that you could have those threads do anything useful.
Update
Okay, couldn‘t resist. Here‘s my little test program, with a couple embellishments:
public class DieLikeADog {
private static Object s = new Object();
private static int count = 0;
public static void main(String[] argv){
for(;;){
new Thread(new Runnable(){
public void run(){
synchronized(s){
count += 1;
System.err.println("New thread #"+count);
}
for(;;){
try {
Thread.sleep(1000);
} catch (Exception e){
System.err.println(e);
}
}
}
}).start();
}
}
}On OS/X 10.5.6 on Intel, and Java 6 5 (see comments), here‘s what I got
New thread #2547
New thread #2548
New thread #2549
Can‘t create thread: 5
New thread #2550
Exception in thread "main" java.lang.OutOfMemoryError: unable to create new native thread
at java.lang.Thread.start0(Native Method)
at java.lang.Thread.start(Thread.java:592)
at DieLikeADog.main(DieLikeADog.java:6)
翻譯：
呃，很多。
What "support" means is another question. If you write a Java program that is just something like
有很多種情況。特定的虛擬機，特定VM，加上VM上通常還有運行時參數。跟操作系統也有點關系：運行的操作系統對多線程有怎樣的支持和對線程的有何種限制？如果VM完全使用操作系統級的線程，那即是紅線程/綠色線程的事情。（譯：這一句不太懂）
何種“支持”意味著另一種問題。如果你寫一個Java程序，就像這樣
class DieLikeADog {
public static void main(String[] argv){
for(;;){
new Thread(new SomeRunaable).start();
}
}
}（先不要抱怨語法上的細節，我在喝今天的第一杯咖啡），你應該期望創建成百上千的運行線程。但是創建一個線程是很昂貴的，調度器開銷也會變得很緊張。不清楚你用這些線程可以做什麽有用的事情。
Update
Okay, couldn‘t resist. Here‘s my little test program, with a couple embellishments:
好吧，受不了反駁了。我給出一個簡單的測試程序。
public class DieLikeADog {
private static Object s = new Object();
private static int count = 0;
public static void main(String[] argv){
for(;;){
new Thread(new Runnable(){
public void run(){
synchronized(s){
count += 1;
System.err.println("New thread #"+count);
}
for(;;){
try {
Thread.sleep(1000);
} catch (Exception e){
System.err.println(e);
}
}
}
}).start();
}
}
}在 OS/X 10.5.6 on Intel, and Java 6 5 (請看評論)環境中, 我的運行結果如下：
New thread #2547
New thread #2548
New thread #2549
Can‘t create thread: 5
New thread #2550
Exception in thread "main" java.lang.OutOfMemoryError: unable to create new native thread
at java.lang.Thread.start0(Native Method)
at java.lang.Thread.start(Thread.java:592)
at DieLikeADog.main(DieLikeADog.java:6)
「翻譯」一篇redis文章引發的翻譯——JVM能支持多少線程？