/usr/include/trilinos/impl/Kokkos_ConcurrentBitset.hpp is in libtrilinos-kokkos-dev 12.12.1-5.
This file is owned by root:root, with mode 0o644.
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//@HEADER
// ************************************************************************
//
// Kokkos v. 2.0
// Copyright (2014) Sandia Corporation
//
// Under the terms of Contract DE-AC04-94AL85000 with Sandia Corporation,
// the U.S. Government retains certain rights in this software.
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// modification, are permitted provided that the following conditions are
// met:
//
// 1. Redistributions of source code must retain the above copyright
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// 2. Redistributions in binary form must reproduce the above copyright
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// documentation and/or other materials provided with the distribution.
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// 3. Neither the name of the Corporation nor the names of the
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY SANDIA CORPORATION "AS IS" AND ANY
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//@HEADER
*/
#ifndef KOKKOS_CONCURRENTBITSET_HPP
#define KOKKOS_CONCURRENTBITSET_HPP
#include <stdint.h>
#include <Kokkos_Atomic.hpp>
#include <impl/Kokkos_BitOps.hpp>
#include <impl/Kokkos_ClockTic.hpp>
namespace Kokkos {
namespace Impl {
struct concurrent_bitset {
public:
// 32 bits per integer value
enum : uint32_t { bits_per_int_lg2 = 5 };
enum : uint32_t { bits_per_int_mask = ( 1 << bits_per_int_lg2 ) - 1 };
// Buffer is uint32_t[ buffer_bound ]
// [ uint32_t { state_header | used_count } , uint32_t bits[*] ]
//
// Maximum bit count is 33 million (1u<<25):
//
// - Maximum bit set size occupies 1 Mbyte
//
// - State header can occupy bits [30-26]
// which can be the bit_count_lg2
//
// - Accept at least 33 million concurrent calls to 'acquire'
// before risking an overflow race condition on a full bitset.
enum : uint32_t { max_bit_count_lg2 = 25 };
enum : uint32_t { max_bit_count = 1u << max_bit_count_lg2 };
enum : uint32_t { state_shift = 26 };
enum : uint32_t { state_used_mask = ( 1 << state_shift ) - 1 };
enum : uint32_t { state_header_mask = uint32_t(0x001f) << state_shift };
KOKKOS_INLINE_FUNCTION static constexpr
uint32_t buffer_bound_lg2( uint32_t const bit_bound_lg2 ) noexcept
{
return bit_bound_lg2 <= max_bit_count_lg2
? 1 + ( 1u << ( bit_bound_lg2 > bits_per_int_lg2
? bit_bound_lg2 - bits_per_int_lg2 : 0 ) )
: 0 ;
}
/**\brief Initialize bitset buffer */
KOKKOS_INLINE_FUNCTION static constexpr
uint32_t buffer_bound( uint32_t const bit_bound ) noexcept
{
return bit_bound <= max_bit_count
? 1 + ( bit_bound >> bits_per_int_lg2 ) +
( bit_bound & bits_per_int_mask ? 1 : 0 )
: 0 ;
}
/**\brief Claim any bit within the bitset bound.
*
* Return : ( which_bit , bit_count )
*
* if success then
* bit_count is the atomic-count of claimed > 0
* which_bit is the claimed bit >= 0
* else if attempt failed due to filled buffer
* bit_count == which_bit == -1
* else if attempt failed due to non-matching state_header
* bit_count == which_bit == -2
* else if attempt failed due to max_bit_count_lg2 < bit_bound_lg2
* or invalid state_header
* or (1u << bit_bound_lg2) <= bit
* bit_count == which_bit == -3
* endif
*
* Recommended to have hint
* bit = Kokkos::Impl::clock_tic() & ((1u<<bit_bound_lg2) - 1)
*/
KOKKOS_INLINE_FUNCTION static
Kokkos::pair<int,int>
acquire_bounded_lg2( uint32_t volatile * const buffer
, uint32_t const bit_bound_lg2
, uint32_t bit = 0 /* optional hint */
, uint32_t const state_header = 0 /* optional header */
) noexcept
{
typedef Kokkos::pair<int,int> type ;
const uint32_t bit_bound = 1 << bit_bound_lg2 ;
const uint32_t word_count = bit_bound >> bits_per_int_lg2 ;
if ( ( max_bit_count_lg2 < bit_bound_lg2 ) ||
( state_header & ~state_header_mask ) ||
( bit_bound < bit ) ) {
return type(-3,-3);
}
// Use potentially two fetch_add to avoid CAS loop.
// Could generate "racing" failure-to-acquire
// when is full at the atomic_fetch_add(+1)
// then a release occurs before the atomic_fetch_add(-1).
const uint32_t state = (uint32_t)
Kokkos::atomic_fetch_add( (volatile int *) buffer , 1 );
const uint32_t state_error =
state_header != ( state & state_header_mask );
const uint32_t state_bit_used = state & state_used_mask ;
if ( state_error || ( bit_bound <= state_bit_used ) ) {
Kokkos::atomic_fetch_add( (volatile int *) buffer , -1 );
return state_error ? type(-2,-2) : type(-1,-1);
}
// Do not update bit until count is visible:
Kokkos::memory_fence();
// There is a zero bit available somewhere,
// now find the (first) available bit and set it.
while(1) {
const uint32_t word = bit >> bits_per_int_lg2 ;
const uint32_t mask = 1u << ( bit & bits_per_int_mask );
const uint32_t prev = Kokkos::atomic_fetch_or(buffer + word + 1, mask);
if ( ! ( prev & mask ) ) {
// Successfully claimed 'result.first' by
// atomically setting that bit.
return type( bit , state_bit_used + 1 );
}
// Failed race to set the selected bit
// Find a new bit to try.
const int j = Kokkos::Impl::bit_first_zero( prev );
if ( 0 <= j ) {
bit = ( word << bits_per_int_lg2 ) | uint32_t(j);
}
else {
bit =
( (word+1) < word_count ? ((word+1) << bits_per_int_lg2) : 0 )
| ( bit & bits_per_int_mask );
}
}
}
/**\brief Claim any bit within the bitset bound.
*
* Return : ( which_bit , bit_count )
*
* if success then
* bit_count is the atomic-count of claimed > 0
* which_bit is the claimed bit >= 0
* else if attempt failed due to filled buffer
* bit_count == which_bit == -1
* else if attempt failed due to non-matching state_header
* bit_count == which_bit == -2
* else if attempt failed due to max_bit_count_lg2 < bit_bound_lg2
* or invalid state_header
* or bit_bound <= bit
* bit_count == which_bit == -3
* endif
*
* Recommended to have hint
* bit = Kokkos::Impl::clock_tic() % bit_bound
*/
KOKKOS_INLINE_FUNCTION static
Kokkos::pair<int,int>
acquire_bounded( uint32_t volatile * const buffer
, uint32_t const bit_bound
, uint32_t bit = 0 /* optional hint */
, uint32_t const state_header = 0 /* optional header */
) noexcept
{
typedef Kokkos::pair<int,int> type ;
if ( ( max_bit_count < bit_bound ) ||
( state_header & ~state_header_mask ) ||
( bit_bound <= bit ) ) {
return type(-3,-3);
}
const uint32_t word_count = bit_bound >> bits_per_int_lg2 ;
// Use potentially two fetch_add to avoid CAS loop.
// Could generate "racing" failure-to-acquire
// when is full at the atomic_fetch_add(+1)
// then a release occurs before the atomic_fetch_add(-1).
const uint32_t state = (uint32_t)
Kokkos::atomic_fetch_add( (volatile int *) buffer , 1 );
const uint32_t state_error =
state_header != ( state & state_header_mask );
const uint32_t state_bit_used = state & state_used_mask ;
if ( state_error || ( bit_bound <= state_bit_used ) ) {
Kokkos::atomic_fetch_add( (volatile int *) buffer , -1 );
return state_error ? type(-2,-2) : type(-1,-1);
}
// Do not update bit until count is visible:
Kokkos::memory_fence();
// There is a zero bit available somewhere,
// now find the (first) available bit and set it.
while(1) {
const uint32_t word = bit >> bits_per_int_lg2 ;
const uint32_t mask = 1u << ( bit & bits_per_int_mask );
const uint32_t prev = Kokkos::atomic_fetch_or(buffer + word + 1, mask);
if ( ! ( prev & mask ) ) {
// Successfully claimed 'result.first' by
// atomically setting that bit.
return type( bit , state_bit_used + 1 );
}
// Failed race to set the selected bit
// Find a new bit to try.
const int j = Kokkos::Impl::bit_first_zero( prev );
if ( 0 <= j ) {
bit = (word << bits_per_int_lg2 ) | uint32_t(j);
}
if ( ( j < 0 ) || ( bit_bound <= bit ) ) {
bit =
( (word+1) < word_count ? ((word+1) << bits_per_int_lg2) : 0 )
| ( bit & bits_per_int_mask );
}
}
}
/**\brief
*
* Requires: 'bit' previously acquired and has not yet been released.
*
* Returns:
* 0 <= used count after successful release
* -1 bit was already released
* -2 state_header error
*/
KOKKOS_INLINE_FUNCTION static
int release( uint32_t volatile * const buffer
, uint32_t const bit
, uint32_t const state_header = 0 /* optional header */
) noexcept
{
if ( state_header != ( state_header_mask & *buffer ) ) { return -2 ; }
const uint32_t mask = 1u << ( bit & bits_per_int_mask );
const uint32_t prev =
Kokkos::atomic_fetch_and( buffer + ( bit >> bits_per_int_lg2 ) + 1
, ~mask
);
if ( ! ( prev & mask ) ) { return -1 ; }
// Do not update count until bit clear is visible
Kokkos::memory_fence();
const int count =
Kokkos::atomic_fetch_add( (volatile int *) buffer , -1 );
return ( count & state_used_mask ) - 1 ;
}
/**\brief
*
* Requires: Bit within bounds and not already set.
*
* Returns:
* 0 <= used count after successful release
* -1 bit was already released
* -2 bit or state_header error
*/
KOKKOS_INLINE_FUNCTION static
int set( uint32_t volatile * const buffer
, uint32_t const bit
, uint32_t const state_header = 0 /* optional header */
) noexcept
{
if ( state_header != ( state_header_mask & *buffer ) ) { return -2 ; }
const uint32_t mask = 1u << ( bit & bits_per_int_mask );
const uint32_t prev =
Kokkos::atomic_fetch_or( buffer + ( bit >> bits_per_int_lg2 ) + 1
, mask
);
if ( ! ( prev & mask ) ) { return -1 ; }
// Do not update count until bit clear is visible
Kokkos::memory_fence();
const int count =
Kokkos::atomic_fetch_add( (volatile int *) buffer , -1 );
return ( count & state_used_mask ) - 1 ;
}
};
}} // namespace Kokkos::Impl
#endif /* #ifndef KOKKOS_CONCURRENTBITSET_HPP */
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