那么,Linux有LWP吗？
解决方法
Threads in Linux are nothing but a flow of execution of the process. A
process containing multiple execution flows is known as multi-threaded
process.For a non multi-threaded process there is only execution flow that is
the main execution flow and hence it is also known as single threaded
process. For Linux kernel,there is no concept of thread. Each thread
is viewed by kernel as a separate process but these processes are
somewhat different from other normal processes. I will explain the
difference in following paragraphs.Threads are often mixed with the term Light Weight Processes or LWPs.
The reason dates back to those times when Linux supported threads at
user level only. This means that even a multi-threaded application was
viewed by kernel as a single process only. This posed big challenges
for the library that managed these user level threads because it had
to take care of cases that a thread execution did not hinder if any
other thread issued a blocking call.Later on the implementation changed and processes were attached to
each thread so that kernel can take care of them. But,as discussed
earlier,Linux kernel does not see them as threads,each thread is
viewed as a process inside kernel. These processes are known as light
weight processes.The main difference between a light weight process (LWP) and a normal
process is that LWPs share same address space and other resources like
open files etc. As some resources are shared so these processes are
considered to be light weight as compared to other normal processes
and hence the name light weight processes.So,effectively we can say that threads and light weight processes are
same. It’s just that thread is a term that is used at user level while
light weight process is a term used at kernel level.From implementation point of view,threads are created using functions
exposed by POSIX compliant pthread library in Linux. Internally,the
clone() function is used to create a normal as well as alight weight
process. This means that to create a normal process fork() is used
that further calls clone() with appropriate arguments while to create
a thread or LWP,a function from pthread library calls clone() with
relevant flags. So,the main difference is generated by using
different flags that can be passed to clone() function.Read more about fork() and clone() on their respective man pages.