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for_each.hpp
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//
reference:
//
- gomp: https://github.com/gcc-mirror/gcc/blob/master/libgomp/iter.c
//
- komp: https://github.com/llvm-mirror/openmp/blob/master/runtime/src/kmp_dispatch.cpp
#
pragma
once
#
include
"
../executor.hpp
"
namespace
tf
{
//
----------------------------------------------------------------------------
//
default parallel for
//
----------------------------------------------------------------------------
//
Function: for_each
template
<
typename
B,
typename
E,
typename
C>
Task
FlowBuilder::for_each
(B&& beg, E&& end, C&& c) {
using
I =
stateful_iterator_t
<B, E>;
using
namespace
std
::string_literals
;
Task task =
emplace
(
[b=std::forward<B>(beg),
e=std::forward<E>(end),
c=std::forward<C>(c)] (Subflow& sf)
mutable
{
//
fetch the stateful values
I beg = b;
I end = e;
if
(beg == end) {
return
;
}
size_t
chunk_size =
1
;
size_t
W = sf.
_executor
.
num_workers
();
size_t
N =
std::distance
(beg, end);
//
only myself - no need to spawn another graph
if
(W <=
1
|| N <= chunk_size) {
std::for_each
(beg, end, c);
return
;
}
if
(N < W) {
W = N;
}
std::atomic<
size_t
>
next
(
0
);
for
(
size_t
w=
0
; w<W; w++) {
//
sf.emplace([&next, beg, N, chunk_size, W, &c] () mutable {
sf.
silent_async
([&next, beg, N, chunk_size, W, &c] ()
mutable
{
size_t
z =
0
;
size_t
p1 =
2
* W * (chunk_size +
1
);
double
p2 =
0.5
/
static_cast
<
double
>(W);
size_t
s0 = next.
load
(std::memory_order_relaxed);
while
(s0 < N) {
size_t
r = N - s0;
//
fine-grained
if
(r < p1) {
while
(
1
) {
s0 = next.
fetch_add
(chunk_size, std::memory_order_relaxed);
if
(s0 >= N) {
return
;
}
size_t
e0
= (chunk_size <= (N - s0)) ? s0 + chunk_size : N;
std::advance
(beg, s0-z);
for
(
size_t
x=s0; x<
e0
; x++) {
c
(*beg++);
}
z =
e0
;
}
break
;
}
//
coarse-grained
else
{
size_t
q =
static_cast
<
size_t
>(p2 * r);
if
(q < chunk_size) {
q = chunk_size;
}
size_t
e0
= (q <= r) ? s0 + q : N;
if
(next.
compare_exchange_strong
(s0,
e0
, std::memory_order_acquire,
std::memory_order_relaxed)) {
std::advance
(beg, s0-z);
for
(
size_t
x = s0; x<
e0
; x++) {
c
(*beg++);
}
z =
e0
;
s0 = next.
load
(std::memory_order_relaxed);
}
}
}
//
}).name("pfg_"s + std::to_string(w));
});
}
sf.
join
();
});
return
task;
}
//
Function: for_each_index
template
<
typename
B,
typename
E,
typename
S,
typename
C>
Task
FlowBuilder::for_each_index
(B&& beg, E&& end, S&& inc, C&& c){
using
I =
stateful_index_t
<B, E, S>;
using
namespace
std
::string_literals
;
Task task =
emplace
(
[b=std::forward<B>(beg),
e=std::forward<E>(end),
a=std::forward<S>(inc),
c=std::forward<C>(c)] (Subflow& sf)
mutable
{
//
fetch the iterator values
I beg = b;
I end = e;
I inc = a;
if
(
is_range_invalid
(beg, end, inc)) {
TF_THROW
(
"
invalid range [
"
, beg,
"
,
"
, end,
"
) with step size
"
, inc);
}
size_t
chunk_size =
1
;
size_t
W = sf.
_executor
.
num_workers
();
size_t
N =
distance
(beg, end, inc);
//
only myself - no need to spawn another graph
if
(W <=
1
|| N <= chunk_size) {
for
(
size_t
x=
0
; x<N; x++, beg+=inc) {
c
(beg);
}
return
;
}
if
(N < W) {
W = N;
}
std::atomic<
size_t
>
next
(
0
);
for
(
size_t
w=
0
; w<W; w++) {
//
sf.emplace([&next, beg, inc, N, chunk_size, W, &c] () mutable {
sf.
silent_async
([&next, beg, inc, N, chunk_size, W, &c] ()
mutable
{
size_t
p1 =
2
* W * (chunk_size +
1
);
double
p2 =
0.5
/
static_cast
<
double
>(W);
size_t
s0 = next.
load
(std::memory_order_relaxed);
while
(s0 < N) {
size_t
r = N - s0;
//
find-grained
if
(r < p1) {
while
(
1
) {
s0 = next.
fetch_add
(chunk_size, std::memory_order_relaxed);
if
(s0 >= N) {
return
;
}
size_t
e0
= (chunk_size <= (N - s0)) ? s0 + chunk_size : N;
auto
s =
static_cast
<I>(s0) * inc + beg;
for
(
size_t
x=s0; x<
e0
; x++, s+=inc) {
c
(s);
}
}
break
;
}
//
coarse-grained
else
{
size_t
q =
static_cast
<
size_t
>(p2 * r);
if
(q < chunk_size) {
q = chunk_size;
}
size_t
e0
= (q <= r) ? s0 + q : N;
if
(next.
compare_exchange_strong
(s0,
e0
, std::memory_order_acquire,
std::memory_order_relaxed)) {
auto
s =
static_cast
<I>(s0) * inc + beg;
for
(
size_t
x=s0; x<
e0
; x++, s+= inc) {
c
(s);
}
s0 = next.
load
(std::memory_order_relaxed);
}
}
}
//
}).name("pfg_"s + std::to_string(w));
});
}
sf.
join
();
});
return
task;
}
}
//
end of namespace tf -----------------------------------------------------
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