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read_watch

READ_WATCH

reads the values from a StopWatch watch

SYNOPSIS
subroutine read_watch (read_result, watch, clock, err)


real, intent(OUT) :: read_result
OR
real, pointer :: read_result(:)
OR
real, pointer :: read_result(:,:)

type (watchtype), intent(IN) :: watch
OR
type (watchtype), intent(IN) :: watch(:)

character(len=*), optional, intent(IN) :: clock
OR
character(len=*), optional, intent(IN) :: clock(:)

integer, optional, intent(OUT) :: err

DESCRIPTION
Returns the value of the specified clocks from the specified watches. The result is returned in read_result . Clocks can be read regardless of whether they are running, stopped or paused.

One or more watches must be specified. The argument watch can be a single variable of type watchtype (see stopwatch(3)) to read one watch, or an array of type watchtype to read several watches. watch can not be a watchgroup because there is no natural order of the watches in the group to use in constructing an array for the result.

The optional argument clock specifies which clocks to read from the specified watch(es). If omitted, the current default clocks (see option_stopwatch(3)) are read. If present, clock must be a character string containing 'cpu', 'user', 'sys', or 'wall', or an array of such character strings.

The type of read_result must agree with the form of the arguments watch and clock:

If watch is a scalar and clock is a scalar, then read_result must be a real scalar.

If watch is an array and clock is a scalar, then read_result must be a pointer to a rank 1 real array. The entry of the result is the specified clock value on watch(i).

If watch is a scalar and clock is either an array or omitted, then read_result must be a pointer to a rank 1 real array. The entry of the result is the value in clock(i) on the specified watch. In the case that clock is omitted, note that the default clocks specify the contents of the result, and the default clocks can be determined using inquiry_stopwatch(3).

If watch is an array and clock is either an array or omitted, then read_result must be a pointer to a rank 2 real array. The entry of the result is the value in clock(j) on watch(i).

If read_result is a pointer to an array, it will be allocated by read_watch , and should be deallocated after use to avoid memory leakage.

DIAGNOSTICS
If present, the optional intent OUT integer argument err returns a status code. The code is the sum of the values listed below.

An error message will be printed to a specified I/O unit (unit 6 by default) if print_errors is TRUE (default is TRUE). The error message contains more detail about the cause of the error than can be obtained from just the status code, so you should set print_errors to TRUE if you have trouble determining the cause of the error.

If abort_errors is TRUE (default is FALSE), the program will terminate on an error condition. Otherwise, the program will continue execution but the watch(es) will not be read.

See option_stopwatch(3) for further information on print_errors, abort_errors and I/O units.

The relevant status codes and messages are:

0
No errors; execution successful.

1
Watch needs to be created. This error occurs if you attempt to read a watch that has been destroyed. The watch must first be created again. See also the comment about watches that have never been created in the BUGS section.

4
Watch is in an unknown state. This occurs if StopWatch does not recognize the state (running, stopped, etc.) that the watch is in. This error should not occur, and indicates an internal bug in StopWatch .

8
Invalid clock type. This occurs if clock is present and one of the specified clocks is not supported by the implementation. See inquiry_stopwatch(3) to determine what clocks are available.

512
Failed to allocate required memory. When read_watch is called with an array or group of watches, temporary memory is allocated. This error occurs if the Fortran allocate statement returns a nonzero status indicating that memory could not be allocated. Avoid memory leaks by always destroying watches and groups before recreating them, and destroying local variable watches and groups before returning from a subroutine.

1024
Error occurred while deallocating memory. This error occurs if the Fortran deallocate statement returns a nonzero status while deallocating temporary memory used for an array or group of watches. The watches are read, but be aware that other problems could develop as a result of the deallocate error.

In addition to the run time diagnostics generated by StopWatch , the following problem may arise:

In Fortran 90, the character strings in an array constructor must all have the same length. Pad three letter clock names with a blank on the right to make a four character string, for example, 'cpu '.

EXAMPLES
type (watchtype) w1, w2(3)
real x
real, pointer :: y(:), z(:,:)
integer errcode

call read_watch(x, w1, 'user')
call read_watch(y, w1, err=errcode)
call read_watch(z, w2, (/'cpu ', 'wall'/), errcode)

deallocate(y, z)

The first call reads the user clock on a single watch. The second call reads the default clocks on a single watch and returns a status code. y is allocated with dimension equal to the number of default clocks. The third call reads the cpu and wall clocks from three watches given as an array and returns a status code. The deallocate statement frees the memory allocated in read_watch .

BUGS
It cannot be determined whether or not a watch variable or watch group has been created (passed as an argument to create_watch or create_watchgroup). If a watch or watch group that has never been created is passed into read_watch, it might generate a Fortran error due to passing a pointer with undefined association status to the Fortran intrinsic function associated. Some compilers will allow this as an extension to the Fortran 90 standard and recognize that the pointer is not associated, in which case the ``Watch needs to be created'' error message is generated.



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william.mitchell@nist.gov