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Old 09-14-2008, 03:18 AM   #1
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Post system calls

in file handling to open a file in c prog we use pen()which
is a system call in linux.....then why do we need to include
headers like fcntl.h,sys/types.h etc???

similarly is pthread_create also a system call???
Old 09-14-2008, 04:52 AM   #2
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You still need to #include the header because for well-formed C code the compiler needs to know the prototype of the function. Headers just have function prototype, #defines, and the like ... they shouldn't actually contain code. Additionally, I believe that the system call is not actually run, but there's a thin wrapper in glibc around it. I'm not sure about that part, though, because it's been awhile since I've looked at it.

I don't think pthread_create is a syscall (at least grepping through arch/x86/kernel/syscall_table_32.S doesn't show it). In Linux each thread is treated as its own process (although it has the same PID, it has a different TID). I suspect that the pthreads library uses the clone(2) system call to do its work (there is an option for cloning with the same PID -- see the man page for more details).


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