mirror of https://gitee.com/openkylin/hdf5.git
95 lines
3.7 KiB
Plaintext
95 lines
3.7 KiB
Plaintext
POSIX Write Order Test Instructions
|
|
===================================
|
|
|
|
Purpose
|
|
-------
|
|
This documents shows the requirments, implementaion design and instructions
|
|
of building and running the POSIX Write Order test. The name of the
|
|
test is twriteorder and it resides in the test/ directory.
|
|
|
|
Requirements
|
|
------------
|
|
The test is to verify that the write order is strictly consistent.
|
|
The SWMR feature requires that the order of write is strictly consistent.
|
|
"Strict consistency in computer science is the most stringent consistency
|
|
model. It says that a read operation has to return the result of the
|
|
latest write operation which occurred on that data item."--
|
|
(http://en.wikipedia.org/wiki/Linearizability#Definition_of_linearizability).
|
|
This is also an alternative form of what POSIX write require that after a
|
|
write operation has returned success, all reads issued afterward should
|
|
get the same data the write has written.
|
|
|
|
Implementation Design
|
|
---------------------
|
|
The test simulates what SWMR does by writing chained blocks and see if
|
|
they can be read back correctly.
|
|
There is a writer process and a read process.
|
|
The file is divided into 2KB partitions. Then writer writes 1 chained
|
|
block, each of 1KB big, in each partition after the first partition.
|
|
Each chained block has this structure:
|
|
Byte 0-3: offset address of its child block. The last child uses 0 as NULL.
|
|
Byte 4-1023: some artificial data.
|
|
The child block address of Block 1 is NULL (0).
|
|
The child block address of Block 2 is the offset address of Block 1.
|
|
The child block address of Block n is the offset address of Block n-1.
|
|
After all n blocks are written, the offset address of Block n is written
|
|
to the offset 0 of the first partition.
|
|
Therefore, by the time the offset address of Block n is written to this
|
|
position, all n chain-linked blocks have been written.
|
|
|
|
The other reader processes will try to read the address value at the
|
|
offset 0. The value is initially NULL(0). When it changes to non-zero,
|
|
it signifies the writer process has written all the chain-link blocks
|
|
and they are ready for the reader processes to access.
|
|
|
|
If the system, in which the writer and reader processes run, the readers
|
|
will always get all chain-linked blocks correctly. If the order of write
|
|
is not maintained, some reader processes may found unexpect block data.
|
|
|
|
Building the Tests
|
|
------------------
|
|
The name of the test is twriteorder in the test directory. It is added
|
|
to the test suite and is built during the "make" process and is run by
|
|
the test_usecases.sh test. Users may inspect test/test_usecases.sh.in
|
|
to see the examples of testing.
|
|
|
|
Running the Tests
|
|
-----------------
|
|
twriteorder test accepts the following options:
|
|
$ ./twriteorder -h
|
|
usage: twriteorder [OPTIONS]
|
|
OPTIONS
|
|
-h Print a usage message and exit
|
|
-l w|r launch writer or reader only. [default: launch both]
|
|
-b N Block size [default: 1024]
|
|
-p N Partition size [default: 2048]
|
|
-n N Number of linked blocks [default: 512]
|
|
|
|
More Examples
|
|
-------------
|
|
|
|
# run test with default parameters and launch both writer and reader
|
|
#processes.
|
|
$ twriteorder
|
|
|
|
# run test with blocksize of 1000 bytes (default is 1024 bytes).
|
|
$ twriteorder -b 1000
|
|
|
|
# run test with partition size of 3000 bytes (default is 2048 bytes).
|
|
$ twriteorder -p 3000
|
|
|
|
# run test with 2000 linked blocks (default is 512 blocks).
|
|
$ twriteorder -n 2000
|
|
|
|
# Launch only the writer process.
|
|
$ twriteorder -l w
|
|
|
|
# Launch only the reader process.
|
|
$ twriteorder -l r
|
|
|
|
Note that if you want to launch the writer and the reader processes
|
|
manually (for example in different machines sharing a common file system),
|
|
you need to start the writer process (-l w) first, and then the reader
|
|
process (-l r).
|
|
|