最近,我在一次采访中被问到一个问题:进程和线程有什么区别?真的,我不知道答案。我想了一会儿,给出了一个非常奇怪的答案。
线程共享相同的内存,而进程不共享。回答完这个问题后,面试官对我邪恶地笑了笑,然后接连问了我几个问题:
问:你知道节目分成哪些部分吗?
我的答案是:是的(认为这很简单)堆栈,数据,代码,堆
问:那么,告诉我:线程共享哪些片段?
我无法回答这个问题,最后只能把它们都说了出来。
请问,谁能就进程和线程之间的区别给出正确的、令人印象深刻的答案?
最近,我在一次采访中被问到一个问题:进程和线程有什么区别?真的,我不知道答案。我想了一会儿,给出了一个非常奇怪的答案。
线程共享相同的内存,而进程不共享。回答完这个问题后,面试官对我邪恶地笑了笑,然后接连问了我几个问题:
问:你知道节目分成哪些部分吗?
我的答案是:是的(认为这很简单)堆栈,数据,代码,堆
问:那么,告诉我:线程共享哪些片段?
我无法回答这个问题,最后只能把它们都说了出来。
请问,谁能就进程和线程之间的区别给出正确的、令人印象深刻的答案?
当前回答
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.
其他回答
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.
线程共享数据和代码,而进程不共享。栈不是为两者共享的。
进程也可以共享内存,更精确的代码,例如Fork()之后,但这是一个实现细节和(操作系统)优化。由多个进程共享的代码将(希望)在第一次写入代码时复制—这被称为写时复制。我不确定线程代码的确切语义,但我假设是共享代码。
Process Thread Stack private private Data private shared Code private1 shared2
代码在逻辑上是私有的,但出于性能原因可能会被共享。 我不能百分之百肯定。
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)
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