cannot find pthread.c in linux folder

Question

I have downloaded kernel and the kernel resides in folder called Linux-2.6.32.28 in which I can find /Kernel/Kthread.c I found Kthread.c but I cannot find pthread.c in Linux-2.6.32.28 I found Kthread.c in Linux-3.13/Kernel and Linux-4.7.2/Kernel

locate pthread.c finds file pthread.c in Computer/usr folder that comes when I install Ubuntu but pthread.c is not available in downloaded folders Linux-2.6.32.28, Linux-3.13, Linux-4.7.2

MORE: There are two sets of function calls. 1. System Calls 2. Library Calls.

For a computer to do any task it has to use hardware resources. So, how library calls differ from system calls?

System calls always use kernel which means hardware. Library calls means no usage of kernel or hardware?

I know that library calls sometimes may resolve to system call.

What I want to know is that, if every set of function calls uses hardware then to what degree system calls will use hardware resources when compared with library calls and vice-versa.

Whether a function call is System or Library, at least hardware resource like RAM has to be utilized. Right?

Answer 1

Read first pthreads(7). It explains you that pthreads are implemented in the C standard library as nptl(7).

The C standard library is the cornerstone of Linux systems, and you might have several variants of it; however, most Linux distributions have only one libc, often the GNU glibc, which contains the NPTL. You might use another C standard library (such as musl-libc or dietlibc). With care, you can have several C standard libraries co-existing on your system.

The C standard library (and every user-space program) is using system calls to interact with the kernel. They are listed in syscalls(2). BTW most C standard library implementations on Linux are free software, so you can study (or even improve) their source code if you want to. You often use a system call thru the small wrapper C function (e.g. write(2)) for it in your C standard library, and even more often thru some higher-level function (e.g. fprintf(3)) provided by your C standard library.

Pthreads are implemented (in the NPTL layer of glibc) using low-level stuff like clone(2) and futex(7) and a bit of assembler code. But you generally won't use these directly unless you are implementing a thread library (like NPTL).

Most programs are using the libc and linking with it (and also with crt0) as a shared library, which is /lib/x86_64-linux-gnu/libc.so.6 on my Debian/Sid/x86-64. However, you might (but you usually don't) invoke system calls directly thru some assembler code (e.g. using a SYSCALL or SYSENTER machine instruction). See also this.

---

The question was edited to also ask

What I want to know is that, if every set of function calls uses hardware then to what degree system calls will use hardware resources

Please read a lot more about operating systems. So read carefully Operating Systems: Three Easy pieces (a freely downloadable textbook) and read about Instruction Set Architecture and Computer Architecture. Study several of them, e.g. x86-64 and RISC-V (or ARM, PowerPC, etc...). Read about CPU modes and virtual memory.

You'll find out that the OS manages physical resources (including RAM and cores of processors). Each process has its own virtual address space. So from a user-space point of view, a process don't use directly hardware (e.g. it runs in virtual address space, not in RAM), it runs in some virtual machine (provided by the OS kernel) defined by the system calls and the ISA (the unpriviledged machine instructions).

Whether a function call is System or Library, at least hardware resource like RAM has to be utilized. Right?

Wrong, from a user-space point of view. All hardware resources are (by definition) managed by the operating system (which provides abstractions thru system calls). An ordinary application executable program uses the abstractions and software resources (files, processes, file descriptors, sockets, memory mappings, virtual address space, etc etc...) provided by the OS.

^{(so several books are required to really answer your questions; I gave some references, please follow them and read a lot more; we can't explain everything here)}

Answer 2

Regarding your second cluster of questions: Everything a computer does is ultimately done by hardware. But we can make some distinctions between different kinds of hardware within the computer, and different kinds of programs interacting with them in different ways.

A modern computer can be divided into three major components: central processing unit (CPU), main memory (random access memory, RAM), and "peripherals" such as disks, network transceivers, displays, graphics cards, keyboards, mice, etc. Things that the CPU and RAM can do by themselves without involving peripherals in any way are called computation. Any operation involving at least one peripheral is called input/output (I/O). All programs do some of both, but some programs mostly do computation, and other programs mostly do I/O.

A modern operating system is also divided into two major components: the kernel, which is a self-contained program that is given special abilities that no other program has (such as the ability to communicate with peripherals and the ability to control the allocation of RAM), and is responsible for supervising execution of all the other programs; and the user space, which is an unbounded set of programs that have no such special abilities.

User space programs can do computation by themselves, but to do I/O they must, essentially, ask the kernel to do it for them. A system call is a request from a user-space program to the kernel. Many system calls are requests to perform I/O, but the kernel can also be requested to do other things, such as provide general information, set up communication channels among programs, allocate RAM, etc. A library is a component of a user space program. It is, essentially, a collection of "functions" that someone else has written for you, that you can use as if you wrote them yourself. There are many libraries, and most of them don't do anything out of the ordinary. For instance, zlib is a library that (provides functions that) compress and uncompress data.

However, "the C library" is special because (on all modern operating systems, except Windows) it is responsible for interacting directly with the kernel. Nearly all programs, and nearly all libraries, will not make system calls themselves; they will instead ask the C library to do it for them. Because of this, it can often be confusing trying to tell whether a particular C library function does all of its work itself or whether it "wraps" one or more system calls. The pthreads functions in particular tend to be a complicated tangle of both. If you want to learn how operating systems are put together at their lower levels, I recommend you start with something simpler, such as how the stdio.h "buffered I/O" routines (fopen, fclose, fread, fwrite, puts, etc) ultimately call the unistd.h/fcntl.h "raw I/O" routines (open, close, read, write, etc) and how the latter set of functions are just wrappers around system calls.

(Assigning the task of wrapping system calls to the runtime library for the C programming language is a historical accident and we probably wouldn't do it that way again if we were going to start over from scratch.)

Answer 3

pthread is POSIX thread. It is a library that helps application to create threads in OS. Kthread in kernel source code is for kernel threads in linux.

POSIX is a standard defined by IEEE to maintain the compatibility between different OS.

So pthread source code cannot be seen in linux kernel source code.

you may refer this link for pthread source code http://www.gnu.org/software/hurd/libpthread.html