线程共享堆(有一个关于线程特定堆的研究)，但当前的实现共享堆。(当然还有代码)

线程共享代码、数据段和堆，但不共享堆栈。

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

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.

真正需要指出的是，这个问题有两个方面——理论方面和实现方面。

首先，让我们看看理论方面。您需要从概念上理解进程是什么，才能理解进程和线程之间的区别以及它们之间共享的内容。

我们从Tanenbaum的2.2.2节现代操作系统3e中的经典线程模型中获得以下内容:

流程模型基于两个独立的概念:资源 分组和执行。有时把它们分开是有用的; 这就是线程....的由来

他继续说:

One way of looking at a process is that it is a way to group related resources together. A process has an address space containing program text and data, as well as other resources. These resource may include open files, child processes, pending alarms, signal handlers, accounting information, and more. By putting them together in the form of a process, they can be managed more easily. The other concept a process has is a thread of execution, usually shortened to just thread. The thread has a program counter that keeps track of which instruc­tion to execute next. It has registers, which hold its current working variables. It has a stack, which contains the execution history, with one frame for each proce­dure called but not yet returned from. Although a thread must execute in some process, the thread and its process are different concepts and can be treated sepa­rately. Processes are used to group resources together; threads are the entities scheduled for execution on the CPU.

他进一步提供了以下表格:

Per process items             | Per thread items
------------------------------|-----------------
Address space                 | Program counter
Global variables              | Registers
Open files                    | Stack
Child processes               | State
Pending alarms                |
Signals and signal handlers   |
Accounting information        |

以上就是线程工作所需要的。正如其他人指出的那样，像段这样的东西是依赖于操作系统的实现细节的。

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。