msync(2)msync(2)NAMEmsync() - synchronize the memory of a mapped file with physical storage
SYNOPSIS
Parameters
addr With len, specifies the region to be synchronized.
len With addr, specifies the region to be synchronized.
flags Specifies one of the following values:
Performs asynchronous writes.
The function synchronizes the file contents to
match the current contents of the memory region.
If flags is the function may return immediately
once all write operations have been scheduled.
· All write references to the memory region made
prior to the call are visible by subsequent
read operations on the file.
· It is unspecified whether writes to the same
portion of the file prior to the call are vis‐
ible by read references to the memory region.
· It is unspecified whether unmodified pages in
the specified range are also written to the
underlying hardware.
Performs synchronous writes.
The function synchronizes the file contents to
match the current contents of the memory region.
If flags is the function does not return until
all write operations are completed.
· All write references to the memory region made
prior to the call are visible by subsequent
read operations on the file.
· It is unspecified whether writes to the same
portion of the file prior to the call are vis‐
ible by read references to the memory region.
· It is unspecified whether unmodified pages in
the specified range are also written to the
underlying hardware.
Invalidates mappings.
The function synchronizes the contents of the
memory region to match the current file contents.
· All writes to the mapped portion of the file
made prior to the call are visible by subse‐
quent read references to the mapped memory
region.
· It is unspecified whether write references
prior to the call, by any process, to memory
regions mapped to the same portion of the file
using are visible by read references to the
region.
DESCRIPTION
The 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.
addr and len specify the region to be synchronized. If these are not
the address and length of a region created by a previous successful
call to returns an error. The behavior of upon a region created with
the or flags is undefined.
If causes any write to the file, then the file's st_ctime and st_mtime
fields are marked for update.
Performance Considerations
The following performance considerations only apply when using the
option with These performance constraints do not apply when either or
are exclusively used with
Direct read/write references to portions of a mapped memory region cur‐
rently undergoing an operation (with specified), may be blocked until
all scheduled write operations are completed. This is especially true
when performing an operation across a relatively large address range
that requires many individual write operations to be scheduled out to
the underlying hardware. HP-UX will schedule a separate write opera‐
tion for each contiguous group of modified pages on disk. As more
write operations are queued out to the device, the overall suspension
time of direct read/write references to the same portions of the memory
region will generally increase.
The suspension times of direct read/write references can be reduced by
issuing requests over smaller portions of the memory region, but issu‐
ing them more frequently than a corresponding larger synchronization
request. This will serve to more evenly distribute I/O activity across
the mapped file, while reducing the number of write operations per
RETURN VALUE
returns the following values:
Successful completion.
Failure.
is set to indicate the error.
ERRORS
The function will fail if:
A transient error occurred while reading from or writing to the
file system.
Some or all of the addresses in the range starting at
addr and continuing for len bytes are
locked, and is specified.
The addr argument is not a multiple of the page
size as returned by
The address range specified by
addr and len was not created by a successful
call to
The value of flags is invalid.
An I/O error occurred while reading from or writing to the file
system.
Some or all the addresses in the range
[addr, addr+len] are invalid for the address
space of the process. Or, pages that are
not mapped are specified.
APPLICATION USAGE
The function should be used by programs that require a memory object to
be in a known state. For example, in building transaction facilities.
Normal system activity can cause pages to be written to disk. There‐
fore, there are no guarantees that is the only control over when pages
are or are not written to disk.
AUTHOR
was developed by HP, AT&T, and OSF.
SEE ALSOmmap(2), sysconf(2), <sys/mman.h>.
STANDARDS CONFORMANCECHANGE HISTORY
First released in Issue 4, Version 2.
msync(2)
