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DATAPOOL(5)							   DATAPOOL(5)

NAME    [Toc]    [Back]

     DATAPOOL -	Fortran	Interprocess Data Sharing

TOPIC    [Toc]    [Back]

     This man page is intended to be both a quick reference and	a source of
     detailed information on Fortran datapool usage.  It is divided into 4

     Datapool Definition and Syntax

     Rules and Usage Description

     Detailed Operation

     Useful Information

Datapool definition and	syntax
     The Fortran DATAPOOL statement is a way for different processes to	access
     the same pool of common symbols. Any processes can	access the shared
     datapool by linking with the datapool DSO (Dynamic	Shared Object).

     A DATAPOOL	statement has the following syntax:

	  DATAPOOL [/[dp]/] nlist [[,]/[dp]/ nlist] ...

     where dp is the datapool name and nlist is	a list of variable names,
     array names, array	declarators, or	records.  A blank datapool, which is
     unique by itself, is defined by omitting the name dp.

     Syntactically, a datapool has similar form	to a common block declaration.
     However, in a common block, the common block variables are	associated
     with the same common block	declared in other program units	by their
     relative position in the common block, regardless of the declared
     symbolic names.  In a datapool, the datapool variables are	associated
     with declarations in other	program	units by their symbolic	names,
     regardless	of the relative	order, sizes, and number of variables declared
     in	the datapool for that particular program unit.	Also, no datapool
     variables can be initialized with a DATA statement.

Rules and Usage	Description
     To	use datapools, the user	must follow these steps:

     * Put each	blockdata containing one or more datapool definitions in a
       Fortran source file.

     * Compile the Fortran source file to create the object file (.o file).
       using the "-G 0"	option.

									Page 1

DATAPOOL(5)							   DATAPOOL(5)

     * Run the ld command:

	  ld -soname datapoolfile.so -shared	   \
	       -noivpad	-G 0 -o	datapoolfile.so	\
	       -init _init_dp_datapoolfile_	   \
	       -fini _unmap_dp__		   \

       where datapoolfile is the name of the Fortran source file without the
       .f extension.  This will	create the datapool DSO	file datapoolfile.so.

     * Compile the rest	of the Fortran program with "-G	0" option.

     * Link all	the Fortran objects with the selected datapool DSO's.  Note
       that the	.o files created from the datapool source files	do need	to be
       linked to create	the executable.

     * When the	program	is run the default directory for the shared mapped
       data is /usr/tmp.  The user can change this by setting the environment
       variable	DATAPOOL_DIR to	point to the desired directory.

Detailed Operation    [Toc]    [Back]

     Each datapool item, when compiled,	will be	turned into a separate
     external symbol so	it can be correctly associated with the	same symbol
     declared in other program units without being affected by its relative
     order in the datapool.

     In	one blockdata subprogram, and in only one, a datapool must be defined
     as	to its exact number of items, sizes, and relative order.   This	will
     be	used as	the basis for sharing the datapool with	other processes
     wishing to	access the same	data.

     Each blockdata can	contain	definitions for	one or more datapools.
     However, each Fortran source file can contain only	one such blockdata.
     Each of those source files	is turned into a DSO which any programs	can
     linked to if they want to access the datapools defined in that blockdata.
     In	other words, all datapools defined in a	single blockdata always	go
     together as a single shared unit.	If the users want to choose the
     datapools separately then they have to be defined in different blockdata,
     and put into separate Fortran source files.

     All datapool variables defined in the blockdata are mapped	to a data file
     which is shared between different processes.  The name of the mapped data
     file is the name of the corresponding Fortran source files	preceded by
     "DP_".  This file is put into the /usr/tmp/ directory as the default, but
     this default directory can	be changed with	the DATAPOOL_DIR environment
     variable.	For example, datapools /a/, /b/, and /c/ are defined in
     blockdata dp_abc_def which	is in the Fortran source file dpabc.f.	 After
     compilation, the file dpabc.f is converted	into dpabc.so which an
     application can link with to share	the datapools /a/, /b/,	and /c/.  At
     runtime, a	mapped data file /usr/tmp/DP_dpabc is created as the default.

									Page 2

DATAPOOL(5)							   DATAPOOL(5)

     After all processes sharing this mapped datapool have terminated the
     mapped file will be removed automatically.	 However, if for any reason a
     process using the datapool	aborts abnormally before it can	run to
     completion, then the mapped file will remain and it will be up to the
     user to remove the	file; otherwise, the next fresh	process	using the
     datapool will pick	up whatever values that	have been mapped into that

Useful information    [Toc]    [Back]

     1)	To create a datapool DSO from the Fortran source file the following
     lines can be added	to the Makefile:

     .SUFFIXES : .so
     FFLAGS = -G 0
     LDFLAGS = -G 0

	  $(FC)	$(FFLAGS) -c $*.f
	  $(LD)	$(LDFLAGS) -soname $@ -shared -noivpad -o $@ \
	      -init _init_dp_$*_ -fini _unmap_dp__ $*.o

     2)	For applications which rely on datapool	variables being	set to zeroes
     at	the beginning of execution, it is prudent to check for the existence
     of	the mapped data	files /usr/tmp/DP_* which might	have been left behind
     by	an abnormal termination	in previous runs.

     3)	Programs running on different machines can share datapools across NFS
     by	setting	DATAPOOL_DIR to	point to the same physical directory.
     However, since I/O	operations are buffered	across NFS, changing a
     datapool variable on one system does not cause the	new value to be
     written immediately in the	data file and so it is not known by a
     different process on another system.  It will be up to the	user to	create
     his own datapool status variable to ensure	the update of the datapool
     variables by another process on a different system.

     4)	At runtime, the	datapool DSO's must be in the search path of rld for
     them to be	found.	The default search path	can be changed by setting the
     environment variable LD_LIBRARY_PATH [see man ld(1)].

     5)	The datapool DSO's cannot be used with IRIX releases before 5.1.1.
     You can get an rld	error message that the DSO's are not found when	a
     datapool application is run on those releases even	when the DSO's exist.

EXAMPLE    [Toc]    [Back]

     C NAME
     C	     testdp.f -	Shared DATAPOOL	test case

									Page 3

DATAPOOL(5)							   DATAPOOL(5)

     C	  Note that both the sizes and the relative order of the datapool
     C	  items	are different from the defined sizes and order in the
     C	  blockdata

	     datapool /hello/ c, b, arr(100,100,3)
	     real*8 arr

	     print *, 'Read arr(1,1,1)', arr(1,1,1)
	     if	(arr(1,1,1) .ne. 42) then
		 arr(1,1,1) = 42

	     print *, "Address Offset =	", %loc(b)-%loc(arr), %loc(c) -%loc(b)
	     call sleep(10)

	     blockdata hellodef
     C	  The relative positions and sizes of the datapool items are
     C	  defined in this blockdata and	nowhere	else.
	     real*8 arr
	     datapool /hello/ arr(100,100,30), b, c

     .SUFFIXES : .so
     CFLAGS = -G 0
     FFLAGS = -G 0
     FFILES = testdp.f hello.f

     default: testdp

     testdp: testdp.o hello.so
	     $(FC) $(FFLAGS) -o	testdp	       testdp.o	hello.so

	     $(FC) $(FFLAGS) -c	$*.f
	     $(LD) -soname $@ -shared -noivpad $*.o -G 0 -o $@ \
	       -init _init_dp_$*_ -fini	_unmap_dp__

     test: default
	     testdp &
	     @ sleep 1
	     testdp &

	     rm	-f *.o core a.out *.so

									Page 4

DATAPOOL(5)							   DATAPOOL(5)

     clobber: clean
	     rm	-f testdp so_locations

AUTHOR    [Toc]    [Back]

     Calvin Vu

									PPPPaaaaggggeeee 5555
[ Back ]
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