Thank you for all your attention on this:), because seems no one
objects, I'm going to assign HARMONY-982 to myself, and start to extend
the portlib.
Paulex Yang wrote:
Sorry I forgot to add the prefix just now.
Paulex Yang wrote:
Hi, all
I raise HARMONY-982
(https://issues.apache.org/jira/browse/HARMONY-982) about the portlib
extension on mmap. And here goes my proposal about the extension,
comments are welcome.
Currently portlib has some mmap support, but the support is limited
in several ways:
1. it only mmap in private(copy_on_write) mode
2. it always mmap whole file
3. it only accepts filename, but nio needs to map a already opened
file descriptor
so that the Harmony's mmap is implemented in platform dependent codes
so far, I think these are good candidates as the portlib extension.
To support the nio's requirement, three current mmap functions need
to be enhanced - hymmap_map_file, hymmap_unmap_file and
hymmap_capabilities, one new method is added: hymmap_msync. Please
see details below:
1. hymmap_map_file
/**
* Map a part of file into memory.
*
* @param [in] portLibrary The port library
* @param [in] file The file descriptor/handle of
the already open file to be mapped
* @param [in] offset The file offset of the part to
be mapped
* @param [in] size The number of bytes to be
mapped, if zero, the whole file is mapped
* @param [in] mappingName The name of the file mapping
object to be created/opened.
* If a named
object is not required, this parameter can be specified as NULL
* @param [in] flags Flags relating to the mapping:
* @args
HYPORT_MMAP_FLAG_READ read only map
* @args
HYPORT_MMAP_FLAG_WRITE read/write map
* @args
HYPORT_MMAP_FLAG_COPYONWRITE copy on write map
* @args
HYPORT_MMAP_FLAG_SHARED share memory mapping with other
processes
* @args
HYPORT_MMAP_FLAG_PRIVATE private memory mapping, do not
share with other processes (implied by HYPORT_MMAP_FLAG_COPYONWRITE)
*
* @return A pointer to the start of the
mapped file or NULL is an error has occurred
*/
void *hymmap_map_file(HYPortLibrary portLibrary, IDATA file, U_64
offset, UDATA size, const char *mappingName, U_32 flags)
This will use CreateFileMapping() and MapViewOfFile() on Windows and
mmap() on Unix to map the file into the process' address space. In
both cases, it will return the address to which the file has been
mapped.
The memory mapping API's on all platforms require an open handle/file
descriptor to the file to be mapped.
The mapAddress parameter has been removed from the original
signature. This was an output parameter from the API containing the
address at which the file has been mapped. However, this is the
return value of the function and was therefore duplication.
2. hymmap_msync
/**
* Synchronise updates to memory mapped file region with file on
disk. The call may wait for the file write
* to complete or this may be scheduled for a later time and the
function return immediately, depending on
* the flags setting
*
* @param [in] portLibrary The port library
* @param [in] start Pointer to the start of the
memory mapped area to be synchronised
* @param [in] length Length of the memory mapped
area to be synchronised
* @param [in] flags Flags controlling the
behaviour of the function:
* @args
HYPORT_MMAP_SYNC_WAIT Synchronous update required, function will not
*
return until file updated. Note that to achieve this on Windows
requires the
*
file to be opened with the FILE_FLAG_WRITE_THROUGH flag
* @args
HYPORT_MMAP_SYNC_ASYNC Asynchronous update required, function returns
*
immediately, file will be updated later
* @args
HYPORT_MMAP_SYNC_INVALIDATE Requests that other mappings of the same
*
file be invalidated, so that they can be updated with the values just
written
*
* @return 0 on success, -1 on failure.
Errors will be reported using the usual port library mechanism
*/
IDATA hymmap_msync(HYPortLibrary portLibrary, void *start, UDATA
length, U_32 flags)
This function will use msync on Unix and FlushViewOfFile on Windows.
3. hymmap_unmap_file
/**
* Unmap previously mapped memory
*
* @param [in] portLibrary The port library
* @param [in] start Pointer to the start of the
memory mapped area
* @param [in] size The length of the mapped area
*/
void hymmap_unmap_file(HYPortLibrary portLibrary, void *start, UDATA
size)
This existing API will be changed to take the start address returned
from hymmap_map_file and the size of the mapped area instead of the
current handle. The handle is not very clear as it is the start
address of the mapped area (equivalent to start) on Windows and a
pointer to a structure containing this and the size on Unix
platforms. Explicitly passing the start address and length will
provide a clearer interface.
4. hymmap_capabilities
/**
* Check the capabilities available for HYMMAP at runtime for the
current platform
*
* @param [in] portLibrary The port library
*
* @return The capabilities available on this
platform
* @args
HYPORT_MMAP_CAPABILITY_READ
* @args
HYPORT_MMAP_CAPABILITY_WRITE
* @args
HYPORT_MMAP_CAPABILITY_COPYONWRITE
*/
I_32 hymmap_capabilities(HYPortLibrary portLibrary)
--
Paulex Yang
China Software Development Lab
IBM
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