file_lock
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An os_file_lock
represents the locking of a region of bytes in a file. A process can request a
read lock or a write lock for a file region. If granted, a read lock prevents
other processes from obtaining a write lock for that region; and, if granted, a
write lock prevents other processes from obtaining a read or a write lock for
that region. If a process requests a lock that is not granted, the process
blocks by default until the lock is available.
To place a lock or check for
other existing locks, use the os_file class.
Declaration
#include <ospace/file/filelock.h>
class os_file_lock
Enums
enum os_file_lock::type_t
{
file_read_lock,
file_write_lock,
file_no_lock
};
Interface
Constructor
os_file_lock(
short type ,
os_off_t length ,
os_off_t offset ,
short whence 0
) bytes of type type (default os_file_lock::file_write_lock
) starting at offset (default 0
) bytes relative to whence (default SEEK_SET
). If length is 0 ,
extends the region to the current end of file.
Constructor
os_file_lock(
const os_file_lock& lock )
Constructs
a lock with the same value as lock .
<
bool
operator<( const os_file_lock& lock )
const
Returns
true if this lock is less than lock
.
=
os_file_lock&
operator=( const os_file_lock& lock )
Assigns
this lock the value of lock .
==
bool
operator==( const os_file_lock& lock )
const
Returns
true if this lock is the same as lock
.
length
os_off_t
length() const
Returns
the length of the locked region. The value 0
indicates the region continues to EOF.
offset
os_off_t
offset() const
Returns
the start position of the locked region. This value is relative to the
whence returned by whence() . For SEEK_SET
and SEEK_END , the start is positive. For SEEK_CUR
, the start is either positive or negative.
print
void
print( ostream& stream )
const
Prints
the lock type (read/write/no lock) to stream .
read_lock
void
read_lock()
Sets
the lock type to read lock.
Throws: os_file_toolkit_error
set_lock
void
set_lock( short type ,
os_off_t length ,
os_off_t offset ,
short whence )
Sets
the lock type to type (default os_file_lock::file_write_lock
) with length length (default 0
) bytes and starting offset (default 0
) bytes relative to whence (default SEEK_SET
). If length is 0 ,
extends the region to the current end of file.
type
short
type() const
Returns
the lock type os_read_lock , os_write_lock
, or os_no_lock .
unlock
void
unlock()
Sets the lock type to
unlocked.
Throws: os_file_toolkit_error
whence
short
whence() const
Returns
the whence value: SEEK_SET , SEEK_CUR
, or SEEK_END , indicating the base for the
relative start location.
write_lock
void
write_lock()
Sets
the lock type to write lock.
UNIX-Specific Interface
Constructor
os_file_lock(
const os_flock_t& lock )
Constructs
a lock from the os_flock_t structure lock
.
(os_flock_t)
operator
os_flock_t() const
Returns
an os_flock_t structure.
process
os_pid_t
process() const
Returns
the pid of the process that currently has the
lock.
Non-Member Functions
<<
ostream&
operator<<( ostream& stream ,
const os_file_lock& lock )
Prints lock
to stream .
Universal Streaming Service
#include <ospace/uss/file.h>
<<
os_bstream&
operator<<( os_bstream& stream ,
const os_file_lock& lock )
Writes lock
to stream .
>>
os_bstream&
operator>>( os_bstream& stream ,
os_file_lock& lock )
Reads lock
from stream .
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