Linux PID 和 TID 的区别
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Difference between PID and TID
提问by apoorv020
What is the difference between PID and TID?
PID 和 TID 有什么区别？
The standard answer would be that PID is for processes while TID is for threads. However, I have seen that some commands use them interchangeably. For example, htophas a column for PIDs, in which PIDs for threads of the same process are shown (with different values). So when does a PID represent a thread or a process?
标准答案是 PID 用于进程，而 TID 用于线程。但是，我已经看到一些命令可以互换使用它们。例如，htop有一个 PID 列，其中显示了同一进程的线程的 PID（具有不同的值）。那么PID什么时候代表线程或进程呢？
采纳答案by rodrigo
It is complicated: pidis process identifier; tidis thread identifier.
它很复杂：pid是进程标识符；tid是线程标识符。
But as it happens, the kernel doesn't make a real distinction between them: threads are just like processes but they share some things (memory, fds...) with other instances of the same group.
但碰巧的是，内核并没有真正区分它们：线程就像进程一样，但它们与同一组的其他实例共享一些东西（内存、fds...）。
So, a tidis actually the identifier of the schedulable object in the kernel (thread), while the pidis the identifier of the group of schedulable objects that share memory and fds (process).
所以，一个tid实际上是内核（线程）中可调度对象的标识符，而pid是共享内存和fds（进程）的一组可调度对象的标识符。
But to make things more interesting, when a process has only one thread (the initial situation and in the good old times the only one) the pidand the tidare always the same. So any function that works with a tidwill automatically work with a pid.
但是为了让事情变得更有趣，当一个进程只有一个线程（最初的情况和过去只有一个线程）时，pid和tid总是相同的。所以任何使用tid 的函数都会自动使用pid。
It is worth noting that many functions/system calls/command line utilities documented to work with pidactually use tids. But if the effect is process-wide you will simply not notice the difference.
值得注意的是，许多被记录为使用pid 的函数/系统调用/命令行实用程序实际上使用tids。但如果影响是整个流程的，您将根本不会注意到差异。
回答by ezpz
pid and tid are the same except when a process is created with a call to clonewith CLONE_THREAD(per the man pages of gettid). In this case, you get a unique thread id but all threads belonging to the same thread group share the same process id.
pid 和 tid 是相同的，除非通过调用clonewith创建进程CLONE_THREAD（根据 的手册页gettid）。在这种情况下，您将获得唯一的线程 ID，但属于同一线程组的所有线程共享相同的进程 ID。
However, I also recall reading (though I cant find the source) that the values returned from getpidmay be cached.
但是，我还记得读过（虽然我找不到来源）从返回的值getpid可能会被缓存。
[UPDATE]
See the NOTESsection herefor a discussion on the effects of caching pids.
[更新] 有关缓存效果的讨论，请参阅此处的NOTES部分。pids
回答by sandeep
Actually, each thread in a Linux process is Light Weight Process (LWP). So, people may call thread as a process... But there is surely a difference. Each thread in a process has a different thread ID (TID) and share the same process ID (PID).
实际上，Linux 进程中的每个线程都是轻量级进程（LWP）。所以，人们可能会称线程为进程......但肯定有区别。进程中的每个线程都有不同的线程 ID (TID) 并共享相同的进程 ID (PID)。
If you are working with pthread library functions, then these functions don't use these TIDs because these are kernel/OS level thread IDs.
如果您正在使用 pthread 库函数，则这些函数不使用这些 TID，因为它们是内核/操作系统级线程 ID。
回答by wick
Just to add to other answers, according to man gettid:
只是为了添加其他答案，根据man gettid：
The thread ID returned by this call is not the same thing as a POSIX thread ID (i.e., the opaque value returned by pthread_self(3)).
此调用返回的线程 ID 与 POSIX 线程 ID 不同（即 pthread_self(3) 返回的不透明值）。
So there are two different things one could mean by TID!
因此，TID 有两种不同的含义！
