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Full Discussion: Atomic lock file creation
Top Forums Programming Atomic lock file creation Post 302274272 by jim mcnamara on Wednesday 7th of January 2009 06:14:25 AM
Old 01-07-2009
sig_atomic_t is a datatype which guarantees atomic operations when basic arithmetic operations, like + -, are involved. This is because the operation takes only one uninterruptible cpu instruction.

That's pretty much all there is for atomic operations defined by the C standard.

fopen fclose, etc, are all part of the C library and are hundreds of cpu instructions long, as well as requiring disk i/o. None of these functions could ever be atomic. They are never guaranteed to be atomic. In UNIX, none of the file I/O system calls like read, write are atomic either. The C library sits on top of these system calls.
 

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lock_init(9r)															     lock_init(9r)

NAME
lock_init - General: Initializes a complex lock SYNOPSIS
#include <kern/lock.h> void lock_init( lock_t lock_structptr, boolean_t can_sleep ); ARGUMENTS
Specifies a pointer to the complex lock structure, lock. The lock structure is an opaque data structure; that is, its associated members are referenced and manipulated by the operating system and not by the user of the complex lock mechanism. Specifies a Boolean value that indicates whether to allow kernel threads to block (sleep) if the complex lock is asserted. You can pass to this argument only the value TRUE (allow kernel threads to block if the lock is asserted). DESCRIPTION
The lock_init routine initializes a complex lock. You identify this lock by declaring a pointer to a complex lock structure and passing it as the first argument. The complex lock structure pointer must be initialized before you can assert read and write operations on the com- plex lock. RETURN VALUES
None FILES
SEE ALSO
Routines: lock_done(9r), lock_read(9r), lock_terminate(9r), lock_try_read(9r), lock_try_write(9r), lock_write(9r) Data Structures: lock(9s) lock_init(9r)
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