MSYNC(3C) Standard C Library Functions MSYNC(3C)
msync - synchronize memory with physical storage
#include <sys/mman.h> int msync
, size_t len
, int flags
function writes all modified copies of pages over the range
[addr, addr + len
) to the underlying hardware, or invalidates any copies
so that further references to the pages will be obtained by the system
from their permanent storage locations. The permanent storage for a
mapping is the file the page is mapped to; the
permanent storage for a modified MAP_PRIVATE
mapping is its swap area.
argument is a bit pattern built from the following values: MS_ASYNC
perform asynchronous writes MS_SYNC
perform synchronous writes MS_INVALIDATE
, the function synchronizes the file
contents to match the current contents of the memory region.
o All write references to the memory region made prior to the
call are visible by subsequent read operations on the file.
o All writes to the same portion of the file prior to the call
may or may not be visible by read references to the memory
o Unmodified pages in the specified range are not written to the
, the function may return immediately once all write
operations are scheduled; if flags
, the function does not
return until all write operations are completed.
, the function synchronizes the contents of the
memory region to match the current file contents.
o All writes to the mapped portion of the file made prior to the
call are visible by subsequent read references to the mapped
o All write references prior to the call, by any process, to
memory regions mapped to the same portion of the file using MAP_SHARED
, are visible by read references to the region.
causes any write to the file, then the file's st_ctime
fields are marked for update.
Upon successful completion, msync()
; otherwise, it returns -1
and sets errno
to indicate the error.
function will fail if: EBUSY
Some or all of the addresses in the range [addr
are locked and MS_SYNC
with the MS_INVALIDATE
Some or all pages in the range [addr
) are locked
for I/O. EINVAL
argument is not a multiple of the page size as
returned by sysconf(3C)
argument is not some combination of MS_ASYNC
An I/O error occurred while reading from or writing to the file
Addresses in the range [addr, addr + len
) are outside the valid
range for the address space of a process, or specify one or
more pages that are not mapped. EPERM MS_INVALIDATE
was specified and one or more of the pages is
locked in memory.
function should be used by programs that require a memory
object to be in a known state, for example in building transaction
Normal system activity can cause pages to be written to disk. Therefore,
there are no guarantees that msync()
is the only control over when pages
are or are not written to disk.
for descriptions of the following attributes:
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|Interface Stability | Standard |
|MT-Level | MT-Safe |
SEE ALSO memcntl(2)
July 24, 2002 MSYNC(3C)