mlock(3C)mlock(3C)NAME
mlock, munlock - lock or unlock pages in memory
SYNOPSIS
#include <sys/types.h>
#include <sys/mman.h>
int mlock(const void *addr, size_t len);
int munlock(const void *addr, size_t len);
DESCRIPTION
mlock locks the pages associated with the address range (addr, addr +
len) into memory. The super-user can lock as many pages as it wishes,
other users are limited to a per process maximum {PLOCK_MAX}. Locks
established with mlock are not inherited by a child process after a fork.
munlock unlocks the pages associated with the address range (addr, addr +
len), regardless of the number of times the pages were locked. Page locks
established by other processes are unaffected, when the pages are shared
amongst multiple processes.
Address addr is not required to be page aligned, as the system
automatically rounds the address down to the nearest page boundary.
mlock or munlock will fail if one or more of the following are true:
[EAGAIN] There was insufficient lockable memory to lock the entire
address range (addr, addr + len). This may occur even though
the amount requested was less than the system-imposed maximum
number of locked pages.
[EBUSY] munlock will fail with this error if the address range
specified has some active I/O initiated by some other process
belonging to same share group.
[ENOMEM] The addresses specified by (addr, addr + len) are not mapped
into the user's address space.
[ENOMEM] The caller was not super-user and the number of pages to be
locked exceeded the per process limit {PLOCK_MAX} [see
intro(2)].
[ENOMEM] The total number of pages locked by the caller would exceed
the maximum resident size for the process [see setrlimit(2)].
[ENOSPC] The address range (addr, addr + len) contains a memory-mapped
file, and there is insufficient space on the device to
allocate the entire file.
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mlock(3C)mlock(3C)SEE ALSOexec(2), exit(2), fork(2), mlockall(3C), munlockall(3C), mmap(2),
mpin(2), munpin(2), plock(2)DIAGNOSTICS
Upon successful completion, the functions mlock and munlock return 0,
otherwise, they return -1 and set errno to indicate the error.
WARNING
The functions mlock/munlock and mpin/munpin provide similar
functionality. The major difference between the two sets is that
mpin/munpin maintains a per page lock counter and mlock/munlock does not.
Developers should choose the set that best suites their application and
stick with it, as mixing the interfaces may result in unexpected
behavior.
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