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