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Contents → REFERENCE MANUAL → Built-In Functions and Commands → Data Handling and Plotting Functions → The Data-Pipe Facility

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spec's data_pipe() function allows integration of external code with spec. With the data-pipe facility, spec sends information to the external program, allows the external program to execute for a time, and then receives information back from the external program. The information can be in the form of a string or a number, and can also include the contents of a spec data group or data array. The handshaking and data transfer between spec and the data-pipe program is done in an overhead module included in the spec distribution that is linked with the external code.

From spec, access to the data-pipe facility is through the data_pipe() function called from the user level. Usage is as follows.

data_pipe(program [, args [, grp_out|arr_out [, grp_in|arr_in ]]])

Initiates or resumes synchronous execution of the special process named program. If program contains a / character, then it contains the complete absolute or relative path name of the program to run. Otherwise the program must be in the SPECD/data_pipe directory, where SPECD is the built-in spec variable containing the path name of spec's auxiliary file directory. You can use the string "." for program as an abbreviation for the same program name as used in the last call to data_pipe().

The string value of args is made available to the user code in the program as described in the next section.

The optional arguments grp_out and grp_in are data group numbers. If grp_out is present, the contents of that group are sent to the data-pipe program. If grp_in is present, it is the number of the data group that will receive values from the data-pipe program. The data-pipe program configures the size of grp_in for an implicit call to data_grp() within data_pipe(). If the grp_in argument is absent, spec will not receive data-group data from the data-pipe program. If grp_out is also absent, group data won't be sent to the data-pipe program. Even without group arguments, the data-pipe program can still return values to spec in the form of assigning a number or string return value to data_pipe().

Either or both of the data group arguments can be replaced with the array arguments arr_out and arr_in. The arrays referred to by these arguments must be the data arrays declared explicitly with the array keyword. When sending array data to the data-pipe program, the array data is first converted to double precision floating point format. The received data is always double, but is converted to fit the declared data type of arr_in. Only as much data as will fit into the array will be assigned. The number of columns in arr_in should match the width of the data sent over by the data-pipe program. If not, the data will still be assigned to the array, but will be misaligned.

Prior to spec release 4.03.13, only one data_pipe() function could be active at a time.

The user C code can be complied and linked using the command

dpmake program [UOBJ=...] [LIBS=...] [optional_make_args]

The command dpmake is a short shell script which invokes the make utility using the makefile data_pipe.mak in the SPECD/data_pipe directory. The file program.c will be compiled and linked with the data-pipe overhead module, and the result placed in an executable file named program. If additional object modules or libraries need to be linked, they can be specified with the UOBJ= or LIBS= parameters. If the tools provided are not sufficient, you can create custom makefiles based on the distributed data_pipe.mak.

After linking program, move it to the SPECD/data_pipe directory for easy access by all users.

The subroutines available from the user C code portion of the data-pipe program are described below.

The skeleton user C-code part of the data-pipe program should contain the following:

#include <user_pipe.h>

user_code(argc, argv)
char    **argv;
{
      ...
}

The include file user_pipe.h contains declarations of the subroutines available in the C code. The file resides in the SPECD/data_pipe directory.

The subroutine user_code() is called by the overhead part of the data-pipe program each time data_pipe() is invoked in spec. The parameter argc is set to the number of space-delimited words present in the string value of the args parameter to data_pipe(). The parameter argv is an array of character pointers that point to each of the argc space-delimited words in the args string. Alternatively, the get_input_string() function (see below) returns the args string in its entirety.

The user_code() routine will be called every time the data_pipe() function is called from spec. The data-pipe program does not exit between calls of user_code(), so you should be careful about allocating memory or opening files each time user_code() is called without freeing the memory or closing the files each time user_code() returns. Alternatively, you can make sure such things are only done the first time user_code() is called.

Besides the argc, argv technique for accessing the args typed in the data_pipe() call, the following function is available:

char * get_input_string()

Returns a pointer to memory holding a copy of the second argument args entered with the call to data_pipe().

If data_pipe() is sending a data group or array to the user code, the following subroutines provide access to the data parameters and values.

int get_group_number()

Returns the group number specified as the data_pipe() grp_out argument. A -2 is returned if an array was specified. A -1 is returned if neither data group or array was specified.

int get_group_npts()

Returns the number of points in the data_pipe() grp_out or the number of rows in arr_out.

int get_group_width()

Returns the number of elements per point in the data_pipe() grp_out or the number of columns in arr_out.

int get_input_data(double *x, int pts, int wid)

Transfers data from the grp_out or arr_out specified in the call to data_pipe() to the memory area indicated by the pointer x. The pointer x is treated as an array dimensioned as x[pts][wid]. If the data group/array has more points/rows than pts or more elements/columns than wid, only as many points/rows or elements/columns as are available in the data group/array are copied. Data from only a single element/column may be retrieved using one or more calls of get_input_elem() below. If the data in the data group from spec is float rather than double (which depends on spec's installation configuration), float-to-double conversion is done within the call to get_input_data(). The return value is the number of points/rows copied.

int get_input_elem(double *x, int pts, int el)

Transfers one element of the data from the grp_out or arr_out specified in the call to data_pipe() to the memory area indicated by the pointer x. No more than pts points are copied from element/column el of the the data group/array. If the data in the data group from spec is float rather than double (which depends on spec's installation configuration), float-to-double conversion is done within the call to get_input_data(). The return value is the number of points/rows copied.

The following subroutines allow you to send group/array data back to spec when data_pipe() is invoked with a grp_in or arr_in argument. For a data group, the call to data_pipe() will implicitly call data_grp() to configure the size of the return group according to the parameters set in the following subroutines. For an array, the array must already be declared and dimensioned.

There are two ways to send group/array data back to spec. The subroutine set_return_data() allows you to send the entire data group in one call that passes both a pointer to the data and the data group size to the data-pipe program overhead code. Alternatively, you can use the set_return_group() subroutine to configure the data group/array size, followed by one or more calls to set_return_elem() to set one element/column of the data group/array at a time.

int get_return_group_number()

Returns the group number specified as the data_pipe() grp_in argument. A -2 is returned if an array was specified. A -1 is returned if neither data group or array was specified.

void set_return_data(double *x, int pts, int wid, int last)

Configures the return data group and copies the data at the same time. The pointer x is considered as an array of dimension x[pts][wid] for the purpose of transferring data to the data group. The argument last sets the index number of the last element added to the group, which is used by the various data analysis and plotting functions available in spec.

void set_return_group(int pts, int wid)

Configures the size of the return data group without copying data. This subroutine must be called once before calling set_return_elem() below.

void set_return_elem(double *x, int pts, int el, int last)

Copies one element to the return data group, which must have been previously configured by a call of set_return_group(), above. If the parameters pts or el exceed the values configured, or if the return group hasn't been configured, the subroutine returns -1. Otherwise zero is returned.

You can set the value that the data_pipe() function returns in spec from the user C code in your data-pipe process. You can have data_pipe() return a number or a string or, if necessary, reset to command level. If no explicit return value is assigned in the user C code, data_pipe() returns zero.

int set_return_string(char *s)

Sets the return value of data_pipe() to the string s. This subroutine returns -1 if memory could not be obtained for the string s, otherwise it returns zero.

void set_return_value(double v)

Sets the return value of data_pipe() to the value v.

void do_error_return()

Calling this subroutine from the user C code causes control to pass back to spec without returning data group or array values, if they have been set. The return value of data_pipe() will be the value set by set_return_value() above, if such a value has been set, otherwise the return value of data_pipe() will be -1. This subroutine does not return.

void do_abort_return()

Calling this subroutine from the user C code causes control to pass back to spec without returning data group or array values, if they has been set. In spec, there is no return from data_pipe(), rather spec resets to command level. This subroutine does not return.

void do_quit_return()

Calling this subroutine from the user C code causes control to pass back to spec normally as if user_code() returned normally, but the data-pipe program will then exit. This subroutine does not return.

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