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Overview |
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Group |
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Quick Info
Windows NT
| Yes
| Win95
| No
| Win32s
| No
| Import Library
| kernel32.lib
| Header File
| winbase.h
| Unicode
| No
| Platform Notes
| None
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VirtualLock
The VirtualLock function locks the specified region of the process's virtual address space
into memory, ensuring that subsequent access to the region will not incur a page
fault.
BOOL VirtualLock(
LPVOID lpAddress,
| // address of first byte of range to lock
| DWORD dwSize
| // number of bytes in range to lock
| );
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Parameters
lpAddress
Points to the base address of the region of pages to be locked.
dwSize
Specifies the size, in bytes, of the region to be locked. The region of
affected pages includes all pages that contain one or more bytes in the range from
the lpAddress parameter to (lpAddress+dwSize). This means that a 2-byte range straddling a page boundary causes both pages
to be locked.
Return Values
If the function succeeds, the return value is nonzero.
If the function fails, the return value is zero. To get extended error
information, call GetLastError.
Remarks
All pages in the specified region must be committed. Memory protected with the
PAGE_NOACCESS flag cannot be locked.
Locking pages into memory may degrade the performance of the system by
reducing the available RAM and forcing the system to swap out other critical pages to
the paging file. By default, a process can lock a maximum of 30 pages. The
default limit is intentionally small to avoid severe performance degradation.
Applications that need to lock larger numbers of pages must first call the SetProcessWorkingSetSize function to increase their minimum and maximum working set sizes. The maximum
number of pages that a process can lock is equal to the number of pages in its
minimum working set minus a small overhead.
Pages that a process has locked remain resident even when the process is idle
for extended periods.
To unlock a region of locked pages, use the VirtualUnlock function. Locked pages are automatically unlocked when the process
terminates.
This function is not like the GlobalLock or LocalLock function in that it does not increment a lock count and translate a handle
into a pointer. There is no lock count for virtual pages, so multiple calls to
the VirtualUnlock function are never required to unlock a region of pages.
Windows 95:
On Windows 95, the VirtualLock function is implemented as a stub that has no effect and always returns TRUE.
See Also
GlobalLock, LocalLock, SetProcessWorkingSetSize, VirtualUnlock
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Unix Manual Pages
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