大家在分析 dump 时，总少不了用 !t 命令看线程列表，比如下面的输出。.
0:000> !t
ThreadCount: 4
UnstartedThread: 0
BackgroundThread: 3
PendingThread: 0
DeadThread: 0
Hosted Runtime: no
Lock
DBG ID OSID ThreadOBJ State GC Mode GC Alloc Context Domain Count Apt Exception
0 1 558 008DB6B8 2a020 Cooperative 0299ACAC:0299BD60 00955aa8 -00001 MTA
6 2 16ec 00966000 2b220 Preemptive 00000000:00000000 00955aa8 -00001 MTA (Finalizer)
7 3 3e34 0097F0F0 102a220 Preemptive 00000000:00000000 00955aa8 -00001 MTA (Threadpool Worker)
8 4 269c 05C0D688 1029220 Preemptive 00000000:00000000 00955aa8 -00001 MTA (Threadpool Worker)
从输出信息看，有一列叫 GC Mode ，可以观察到它的状态值分别为 Cooperative 和 Preemptive，那这两个状态到底代表着什么呢？为了更好的演示，我先上一段它的测试代码：
public static void Main()
{
while (true)
{
}
Console.ReadLine();
}
从 GC Mode 名字看，应该和 GC 回收有关，确实是这样,接下来我们一一解读下。
1. Preemptive
翻译过来就是 抢占，那 抢占 谁呢？很显然是抢占 托管线程，让它处于某一种抑制状态，简而言之就是如果一个 托管线程 切换到 Preemptive 之后，此时它就无法访问 托管堆 了，这么做的好处，自然就是让 GC 在托管堆上自由的标记，在计划，回收和压缩阶段而不受托管线程干扰，目前来说有两种情况线程会处于 Preemptive 状态。
1)GC 触发阶段
这个我已经聊过了，GC 要标记对象可达时，必须要让所有线程处于暂停（Preemptive）状态。
2) 切换到非托管代码
我们在用 C# 编程时，经常要和 非托管代码 交互，比如 C++，Python，换句话说，线程可能需要从托管层切换到非托管层，当切换到后者时，CLR也需要将线程从 Cooperative 切换到 Preemptive。
2. Cooperative
翻译过来就是 协作，那谁和谁协作呢？自然就是 GC 和 用户线程 合作，这种状态的 线程 是可以自由访问 托管堆 ，经常在 GC 回收结束后，将线程转成切换到 Cooperative 。
不知道大家现在可明白啦，最后补充一下，如果你看到所有的线程都处于 Preemptive 状态，有很大可能是 GC 触发啦，比如下面这样。
0:295> !t
ThreadCount: 200
UnstartedThread: 180
BackgroundThread: 19
PendingThread: 180
DeadThread: 0
Hosted Runtime: no
Lock
ID OSID ThreadOBJ State GC Mode GC Alloc Context Domain Count Apt Exception
0 1 17a8 000001f1c7065990 26020 Preemptive 0000000000000000:0000000000000000 000001f1c703bdd0 0 STA
2 2 2114 000001f1c708ef50 2b220 Preemptive 0000000000000000:0000000000000000 000001f1c703bdd0 0 MTA (Finalizer)
4 3 1f70 000001f1c72b7ba0 1029220 Preemptive 0000000000000000:0000000000000000 000001f1c703bdd0 0 MTA (Threadpool Worker)
5 4 2058 000001f1e5b1e840 1039220 Preemptive 0000000000000000:0000000000000000 000001f1c703bdd0 0 Ukn (Threadpool Worker)
6 5 2860 000001f1e5b4cb40 2b220 Preemptive 0000000000000000:0000000000000000 000001f1c703bdd0 0 MTA
9 6 a18 000001f1e5b83470 2b220 Cooperative 0000000000000000:0000000000000000 000001f1c703bdd0 1 MTA (GC)
8 7 2aec 000001f1e5b593b0 1039220 Preemptive 0000000000000000:0000000000000000 000001f1c703bdd0 0 Ukn (Threadpool Worker)
10 10 2090 000001f1e5b27910 1039220 Preemptive 0000000000000000:0000000000000000 000001f1c703bdd0 0 Ukn (Threadpool Worker)
11 11 99c 000001f1e5b85af0 1039220 Preemptive 0000000000000000:0000000000000000 000001f1c703bdd0 0 Ukn (Threadpool Worker)
12 12 170c 000001f1e5ba5b20 1039220 Preemptive 0000000000000000:0000000000000000 000001f1c703bdd0 0 Ukn (Threadpool Worker)
13 13 1798 000001f1e5b39360 1039220 Preemptive 0000000000000000:0000000000000000 000001f1c703bdd0 0 Ukn (Threadpool Worker)
14 14 2ae4 000001f1e5b31b70 1029220 Preemptive 0000000000000000:0000000000000000 000001f1c703bdd0 0 MTA (Threadpool Worker)
15 15 2ebc 000001f1e5b30320 1039220 Preemptive 0000000000000000:0000000000000000 000001f1c703bdd0 0 Ukn (Threadpool Worker)
16 16 e00 000001f1e5ba24e0 1029220 Preemptive 0000000000000000:0000000000000000 000001f1c703bdd0 0 MTA (Threadpool Worker)
17 17 123c 000001f1e5ba2cb0 1029220 Preemptive 0000000000000000:0000000000000000 000001f1c703bdd0 0 MTA (Threadpool Worker)
18 18 2aa0 000001f1e5b67430 1039220 Preemptive 0000000000000000:0000000000000000 000001f1c703bdd0 0 Ukn (Threadpool Worker)
19 19 2990 000001f1ef8597a0 1039220 Preemptive 0000000000000000:0000000000000000 000001f1c703bdd0 0 Ukn (Threadpool Worker)
20 20 1568 000001f1ef857860 1029220 Preemptive 0000000000000000:0000000000000000 000001f1c703bdd0 0 MTA (Threadpool Worker)
21 21 1f20 000001f1ef85a740 21220 Preemptive 0000000000000000:0000000000000000 000001f1c703bdd0 0 Ukn
115 26 11e4 000001f1efb5bea0 8029220 Preemptive 0000000000000000:0000000000000000 000001f1c703bdd0 0 MTA (Threadpool Completion Port)
116 24 2d34 000001f1efb5a730 1400 Preemptive 0000000000000000:0000000000000000 000001f1c703bdd0 0 Ukn
