SHMEM_GET(3)

✨ NAME ✨ — the get-into-your-inbox squad 💌

okay so you're looking at SHMEM_GET(3) from Open MPI, and this whole fam transfers data from a specified processing element (PE). no cap, that's the whole vibe. the squad is:

• shmem_character_get(3)
• shmem_complex_get(3)
• shmem_double_get(3)
• shmem_float_get(3)
• shmem_get4(3)
• shmem_get8(3)
• shmem_get32(3)
• shmem_get64(3)
• shmem_get128(3)
• shmem_getmem(3)
• shmem_int_get(3)
• shmem_integer_get(3)
• shmem_logical_get(3)
• shmem_long_get(3)
• shmem_longdouble_get(3)
• shmem_longlong_get(3)
• shmem_real_get(3)
• shmem_short_get(3)

and yeah, they all transfer data from a specified processing element (PE). periodt 💅

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✨ SYNOPSIS ✨ — the signatures, bestie 🎀

C or C++:

#include <mpp/shmem.h>

void shmem_get32(void *target, const void *source,
  size_t len, int pe);

void shmem_get64(void *target, const void *source,
  size_t len, int pe);

void shmem_get128(void *target, const void *source,
  size_t len, int pe);

void shmem_getmem(void *target, const void *source,
  size_t len, int pe);

void shmem_int_get(int *target, const int *source,
  size_t len, int pe);

void shmem_double_get(double *target, const double *source,
  size_t len, int pe);

void shmem_float_get(float *target, const float *source,
  size_t len, int pe);

void shmem_long_get(long *target, const long *source,
  size_t len, int pe);

void shmem_longdouble_get(long double *target,
  const long double *source, size_t len, int pe);

void shmem_longlong_get(long long *target,
  const long long *source, size_t len, int pe);

void shmem_short_get(short *target,
  const short *source, size_t len, int pe);

Fortran:

INCLUDE "mpp/shmem.fh"

INTEGER len, pe

CALL SHMEM_CHARACTER_GET(target, source, len, pe)

CALL SHMEM_COMPLEX_GET(target, source, len, pe)

CALL SHMEM_DOUBLE_GET(target, source, len, pe)

CALL SHMEM_GET4(target, source, len, pe)

CALL SHMEM_GET8(target, source, len, pe)

CALL SHMEM_GET32(target, source, len, pe)

CALL SHMEM_GET64(target, source, len, pe)

CALL SHMEM_GET128(target, source, len, pe)

CALL SHMEM_GETMEM(target, source, len, pe)

CALL SHMEM_INTEGER_GET(target, source, len, pe)

CALL SHMEM_LOGICAL_GET(target, source, len, pe)

CALL SHMEM_REAL_GET(target, source, len, pe)

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✨ DESCRIPTION ✨ — what it actually does 🦋

so the shmem_get routines transfer nelems elements of the data object at address source on the remote PE pe, to the data object at address target on the local PE. these routines return after the data has been copied to address target on the local PE. like, they're done when the copy is done, bestie. ✨

the arguments are as follows:

• target — local data object to be updated.
• source — data object on the PE identified by pe that contains the data to be copied. this data object must be remotely accessible.
• len — number of elements in the target and source arrays. len must be of type integer. if you are using Fortran, it must be a constant, variable, or array element of default integer type.
• pe — PE number of the remote PE. pe must be of type integer. if you are using Fortran, it must be a constant, variable, or array element of default integer type.

the target and source data objects must conform to typing constraints, which are as follows:

• shmem_getmem — Fortran: Any noncharacter type. C: Any data type. len is scaled in bytes.
• shmem_get4, shmem_get32 — Any noncharacter type that has a storage size equal to 32 bits.
• shmem_get8, shmem_get64 — Any noncharacter type that has a storage size equal to 64 bits.
• shmem_get128 — Any noncharacter type that has a storage size equal to 128 bits.
• shmem_short_get — Elements of type short.
• shmem_int_get — Elements of type int.
• shmem_long_get — Elements of type long.
• shmem_longlong_get — Elements of type long long.
• shmem_float_get — Elements of type float.
• shmem_double_get — Elements of type double.
• shmem_longdouble_get — Elements of type long double.
• SHMEM_CHARACTER_GET — Elements of type character. len is the number of characters to transfer. The actual character lengths of the source and target variables are ignored.
• SHMEM_COMPLEX_GET — Elements of type complex of default size.
• SHMEM_DOUBLE_GET — (Fortran) Elements of type double precision.
• SHMEM_INTEGER_GET — Elements of type integer.
• SHMEM_LOGICAL_GET — Elements of type logical.
• SHMEM_REAL_GET — Elements of type real.

if you are using Fortran, data types must be of default size. for example, a real variable must be declared as REAL, REAL*4, or REAL(KIND=4). 🫶

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✨ NOTES ✨ — the lil footnote 🌸

see intro_shmem(3) for a definition of the term remotely accessible. iykyk 💖

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✨ EXAMPLES ✨ — a real one, fr fr 🔥

consider this simple example for Fortran.

PROGRAM REDUCTION
  REAL VALUES, SUM
  COMMON /C/ VALUES
  REAL WORK

  CALL START_PES(0) ! ALLOW ANY NUMBER OF PES
  VALUES = MY_PE() ! INITIALIZE IT TO SOMETHING
  CALL SHMEM_BARRIER_ALL
  SUM = 0.0
  DO I = 0,NUM_PES()-1
    CALL SHMEM_REAL_GET(WORK, VALUES, 1, I)
    SUM = SUM + WORK
  ENDDO
  PRINT *, 'PE ', MY_PE(), ' COMPUTED SUM=', SUM
  CALL SHMEM_BARRIER_ALL
END

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✨ SEE ALSO ✨ — go read these too 👑

• intro_shmem(3)
• shmem_put(3)
• shmem_iget(3)
• shmem_quiet(3)

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mwah 💋 kisses from your SHMEM_GET(3) bestie — source: gitclone, version: Unreleased developer copy, and the footer doesn't list a separate date, so that's the whole tea 🫖✨