mlock(), munlock()

lock or unlock a range of process address space 

Realtime Function


SYNOPSIS

#include <sys/mman.h>

int mlock(const void *addr, size_t len);

int munlock(const void *addr, size_t len);


DESCRIPTION

The mlock() and munlock() functions lock and unlock, respectively, a range of whole pages. This range consists of any whole page containing any part of the address space starting at address addr and continuing for len bytes.

When the mlock() locks the page range, the pages become memory-resident until unlocked or until the process exits or execs another process image.

The munlock() unlocks the page range, regardless of how many times mlock() has been called by the range for any page within the range. When any of the pages within the specified range of a munlock() call are also mapped into the address spaces of other processes, any locks established on those pages by another process are unaffected. When any of the pages within the specified range of a munlock() call are also mapped into other portions of the address space of the calling space outside the range specified, any locks established on those pages via the other mappings are also unaffected by the munlock() call.


PARAMETERS

addr 

Points to a memory address that determines the first page of the page range.

len 

Specifies the size, in bytes, of the address space used to determine the full extent of the specified page range.


RETURN VALUES

On success, the mlock() and munlock() functions return 0. On failure, these functions make no changes to any locks in the address space of the process, return -1, and sets set errno to one of the following:

EAGAIN 

Some or all of the memory identified by the operation could not be locked when the call was made.

EINVAL 

The addr argument is not a multiple of {PAGESIZE}.

ENOMEM 

Some or all of the address range specified by the addr and len arguments does not correspond to valid mapped pages in the address space of the process. This can also be caused if Windows' working set is set too small to make all the required pages memory-resident.

EPERM 

The calling process does not have the appropriate privilege to perform the requested operation.


CONFORMANCE

UNIX 03.


MULTITHREAD SAFETY LEVEL

MT-Safe.


PORTING ISSUES

On the NuTCRACKER Platform, the mlock() and munlock() use Windows' working sets. On Windows, a working set is the set of memory pages in physical RAM that are currently visible to a process. For performance reasons, Windows attempts to keep the size of a working set down. This means that realtime applications may need to increase the size of the working set so that more pages than what Windows defaults to allow can be locked. Of course, with the appropriate privilege (SE_INC_BASE_PRIORITY_NAME), the calling process can call the Win32 SetProcessWorkingSetSize() function to change the size of the working set and then call mlock() again.


AVAILABILITY

PTC MKS Toolkit for Professional Developers
PTC MKS Toolkit for Professional Developers 64-Bit Edition
PTC MKS Toolkit for Enterprise Developers
PTC MKS Toolkit for Enterprise Developers 64-Bit Edition


SEE ALSO

Functions:
exec(), exit(), fork(), mlockall(), munmap()


PTC MKS Toolkit 10.3 Documentation Build 39.