来自维基百科(我认为这对面试官来说是个很好的回答:P)

Threads differ from traditional multitasking operating system processes in that: processes are typically independent, while threads exist as subsets of a process processes carry considerable state information, whereas multiple threads within a process share state as well as memory and other resources processes have separate address spaces, whereas threads share their address space processes interact only through system-provided inter-process communication mechanisms. Context switching between threads in the same process is typically faster than context switching between processes.

通常，线程被称为轻量级进程。如果我们把内存分成三个部分，那么它将是:代码，数据和堆栈。 每个进程都有自己的代码、数据和堆栈部分，由于这种上下文切换时间有点高。为了减少上下文切换的时间，人们提出了线程的概念，它与其他线程/进程共享数据和代码段，并拥有自己的堆栈段。

线程共享代码、数据段和堆，但不共享堆栈。

告诉面试官这完全取决于操作系统的实现。

以Windows x86为例。只有两个段[1]，代码和数据。它们都被映射到整个2GB(线性，用户)地址空间。基础= 0,限制= 2 gb。他们本来可以做一个，但x86不允许一个段同时读/写和执行。所以他们做了两个，并设置CS指向代码描述符，其余(DS, ES, SS等)指向另一个[2]。但两者都指向同样的东西!

面试你的人做了一个隐藏的假设，他/她没有说出来，这是一个愚蠢的伎俩。

所以关于

问:告诉我是哪个线段 分享吗?

细分市场与问题无关，至少在Windows上是这样。线程共享整个地址空间。只有一个堆栈段SS，它指向DS ES CS做的完全一样的东西[2]。比如整个用户空间。0-2GB。当然，这并不意味着线程只有一个堆栈。当然，每个都有自己的堆栈，但x86段并不用于此目的。

也许*nix做一些不同的事情。谁知道呢。这个问题的前提被打破了。

至少对于用户空间是这样的。 从ntsd记事本:cs=001b ss=0023 ds=0023 es=0023

您说得很对，但是线程共享除堆栈之外的所有段。线程有独立的调用堆栈，但是其他线程堆栈中的内存仍然是可访问的，理论上你可以在其他线程的本地堆栈框架中保存内存指针(尽管你可能应该找到一个更好的地方来放置内存!)。

Besides global memory, threads also share a number of other attributes (i.e., these attributes are global to a process, rather than specific to a thread). These attributes include the following: process ID and parent process ID; process group ID and session ID; controlling terminal; process credentials (user and group IDs); open file descriptors; record locks created using fcntl(); signal dispositions; file system–related information: umask, current working directory, and root directory; interval timers (setitimer()) and POSIX timers (timer_create()); System V semaphore undo (semadj) values (Section 47.8); resource limits; CPU time consumed (as returned by times()); resources consumed (as returned by getrusage()); and nice value (set by setpriority() and nice()). Among the attributes that are distinct for each thread are the following: thread ID (Section 29.5); signal mask; thread-specific data (Section 31.3); alternate signal stack (sigaltstack()); the errno variable; floating-point environment (see fenv(3)); realtime scheduling policy and priority (Sections 35.2 and 35.3); CPU affinity (Linux-specific, described in Section 35.4); capabilities (Linux-specific, described in Chapter 39); and stack (local variables and function call linkage information).

摘自:《Linux编程接口:Linux和UNIX系统编程手册》，Michael Kerrisk，第619页