NAME [Toc] [Back]
mlock() - lock a segment of the process virtual address space in
SYNOPSIS [Toc] [Back]
int mlock( const void * addr, size_t len) ;
DESCRIPTION [Toc] [Back]
The mlock() system call allows the calling process to lock a segment
of the process virtual address space into memory. Any addressable
segment of the process' address space may be locked. Locked segments
are immune to all routine swapping.
addr must be a valid address in the process virtual address space.
addr + len must also be a valid address in the process virtual address
Locks are applied at page boundaries that encompass the range from
addr to addr + len. If any address within the range is not valid, an
error is returned and no locks are applied.
munlock() or munlockall() can be used to unlock memory segments (or
all memory segments) locked with mlock().
Regardless of how many times a process locks a page, a single
munlock() or munlockall() will unlock it. An munlock() of a page
within a range specified in an mlock() call results in only the range
specified in the munlock() being unlocked.
When memory is shared by multiple processes and mlocks are applied to
the same physical page by multiple processes, a page remains locked
until the last lock is removed from that page.
Locks applied with mlock() are not inherited by a child process.
The effective user ID of the calling process must be a superuser or
the user must be a member of a group that has the MLOCK privilege (see
getprivgrp(2) and setprivgrp(1M))
Although plock() and the mlock() family of functions may be used
together in an application, each may affect the other in unexpected
ways. This practice is not recommended.
RETURN VALUE [Toc] [Back]
mlock() returns the following values:
0 Successful completion.
-1 Failure. The requested operation is not performed. errno
is set to indicate the error.
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ERRORS [Toc] [Back]
If mlock() fails, errno is set to one of the following values:
[ENOMEM] One or more addresses in the specified range is
not valid within the process address space.
[EAGAIN] There is not enough lockable memory in the system
to satisfy the locking request.
[EINVAL] The len parameter was zero.
[EPERM] The effective user ID of the calling process is
not a superuser and the user does not belong to a
group that has the MLOCK privilege.
EXAMPLES [Toc] [Back]
The following call to mlock() locks the first 10 pages of the calling
process in memory:
SEE ALSO [Toc] [Back]
setprivgrp(1M), getprivgrp(2), mlockall(2), munlock(2), munlockall(2),
STANDARDS CONFORMANCE [Toc] [Back]
mlock(): POSIX Realtime Extensions, IEEE Std 1003.1b
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