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Reduce pvector delta_cell quota on reads. Add example that demonstrates why this is needed.

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Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
This commit is contained in:
Leonardo de Moura 2013-09-12 08:28:24 -07:00
parent 5858c9d5e0
commit cd5e45bae2
2 changed files with 79 additions and 23 deletions
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21
src/tests/util/pvector.cpp
View file

@ -8,8 +8,11 @@ Author: Leonardo de Moura
#include <cstdlib>
#include "test.h"
#include "pvector.h"
#include "timeit.h"
using namespace lean;
// #define PVECTOR_PERF_TEST
static void tst1() {
pvector<int> v;
lean_assert(v.empty());
@ -96,10 +99,21 @@ static void tst2() {
driver(128, 1000, 10000, 0.2, 0.1);
}
// #define PVECTOR_PERF_TEST
#ifdef PVECTOR_PERF_TEST
#include "timeit.h"
static void tst3() {
timeit t(std::cout, "tst3");
unsigned N = 20000;
unsigned M = 20000;
pvector<int> v;
for (unsigned i = 0; i < N; i++) v.push_back(i);
pvector<int> v2 = v;
for (unsigned i = 0; i < N / 2; i++) v2.push_back(i);
// v2 has a long trail of deltas
// Now, we only read v2
unsigned s = 0;
for (unsigned i = 0; i < M; i++) { s += v2[i % v2.size()]; }
}
#ifdef PVECTOR_PERF_TEST
static void perf_vector(unsigned n) {
std::vector<int> q;
for (unsigned i = 0; i < n; i++) {
@ -173,6 +187,7 @@ static void tst_perf2() {
int main() {
tst1();
tst2();
tst3();
#ifdef PVECTOR_PERF_TEST
tst_perf1();
tst_perf2();

79
src/util/pvector.h
View file

@ -30,6 +30,7 @@ class pvector {
cell_kind m_kind;
MK_LEAN_RC();
cell(cell_kind k):m_kind(k), m_rc(0) {}
cell(cell const & c):m_kind(c.m_kind), m_rc(0) {}
void dealloc();
unsigned size() const;
/**
@ -59,6 +60,10 @@ class pvector {
lean_assert(m_prev);
m_prev->inc_ref();
}
delta_cell(delta_cell const & c):cell(c), m_size(c.m_size), m_quota(c.m_quota), m_prev(c.m_prev) {
lean_assert(m_prev);
m_prev->inc_ref();
}
~delta_cell() { lean_assert(m_prev); m_prev->dec_ref(); }
};
@ -68,6 +73,7 @@ class pvector {
*/
struct pop_cell : public delta_cell {
pop_cell(cell * prev):delta_cell(cell_kind::PopBack, prev->size() - 1, prev) {}
pop_cell(pop_cell const & c):delta_cell(c) {}
};
/**
@ -77,6 +83,7 @@ class pvector {
struct push_cell : public delta_cell {
T m_val;
push_cell(T const & v, cell * prev):delta_cell(cell_kind::PushBack, prev->size() + 1, prev), m_val(v) {}
push_cell(push_cell const & c):delta_cell(c), m_val(c.m_val) {}
};
/**
@ -87,6 +94,7 @@ class pvector {
unsigned m_idx;
T m_val;
set_cell(unsigned i, T const & v, cell * prev):delta_cell(cell_kind::Set, prev->size(), prev), m_idx(i), m_val(v) {}
set_cell(set_cell const & c):delta_cell(c), m_idx(c.m_idx), m_val(c.m_val) {}
};
static push_cell & to_push(cell * c) { lean_assert(c->kind() == cell_kind::PushBack); return *static_cast<push_cell*>(c); }
@ -101,6 +109,9 @@ class pvector {
cell * m_ptr;
pvector(cell * d):m_ptr(d) { lean_assert(m_ptr); m_ptr->inc_ref(); }
/** \brief Return true iff the cell associated with this vector is shared */
bool is_shared() const { return m_ptr->get_rc() > 1; }
/** \brief Update the cell (and reference counters) of this vector */
void update_cell(cell * new_cell) {
lean_assert(new_cell);
@ -110,29 +121,26 @@ class pvector {
m_ptr = new_cell;
}
/** \brief Return true iff the cell associated with this vector is shared */
bool is_shared() const { return m_ptr->get_rc() > 1; }
/**
\brief Auxiliary method for \c flat_if_needed.
Given an empty vector \c r, then <tt>flat(c, r)</tt> will
\brief Auxiliary method for \c flat
Given an empty vector \c r, then <tt>flat_core(c, r)</tt> will
store in r the vector represented by cell \c c.
That is, the vector obtained after finding the root cell (aka wrapper for std::vector),
and applying all deltas.
*/
static void flat(cell * c, std::vector<T> & r) {
static void flat_core(cell * c, std::vector<T> & r) {
lean_assert(r.empty());
switch(c->kind()) {
case cell_kind::PushBack:
flat(to_push(c).m_prev, r);
flat_core(to_push(c).m_prev, r);
r.push_back(to_push(c).m_val);
break;
case cell_kind::PopBack:
flat(to_pop(c).m_prev, r);
flat_core(to_pop(c).m_prev, r);
r.pop_back();
break;
case cell_kind::Set:
flat(to_set(c).m_prev, r);
flat_core(to_set(c).m_prev, r);
r[to_set(c).m_idx] = to_set(c).m_val;
break;
case cell_kind::Root:
@ -141,6 +149,18 @@ class pvector {
}
}
/**
\brief Change the representation to a root cell.
*/
void flat() {
lean_assert(m_ptr->kind() != cell_kind::Root);
std::vector<T> r;
flat_core(m_ptr, r);
update_cell(new root_cell());
to_root(m_ptr).m_vector.swap(r);
lean_assert(!is_shared());
}
/**
\brief If the quota associated with m_cell is zero, then
compute a flat representation. That is, represent the vector
@ -149,11 +169,29 @@ class pvector {
void flat_if_needed() {
lean_assert(m_ptr->kind() != cell_kind::Root);
if (static_cast<delta_cell*>(m_ptr)->m_quota == 0) {
std::vector<T> r;
flat(m_ptr, r);
update_cell(new root_cell());
to_root(m_ptr).m_vector.swap(r);
flat();
}
}
/** \brief Update quota based on the cost of a read */
void update_quota_on_read(unsigned cost) {
cost /= 2; // reads are cheaper than writes
if (cost > 0) {
if (cost >= m_ptr->quota()) {
flat();
} else {
if (is_shared()) {
switch (m_ptr->kind()) {
case cell_kind::PushBack: update_cell(new push_cell(to_push(m_ptr))); break;
case cell_kind::PopBack: update_cell(new pop_cell(to_pop(m_ptr))); break;
case cell_kind::Set: update_cell(new set_cell(to_set(m_ptr))); break;
case cell_kind::Root: lean_unreachable(); break;
}
}
lean_assert(!is_shared());
lean_assert(cost < static_cast<delta_cell*>(m_ptr)->m_quota);
static_cast<delta_cell*>(m_ptr)->m_quota -= cost;
}
}
}
@ -183,30 +221,33 @@ public:
/**
\brief Access specified element
\pre i < size()
TODO: Consider if we should reduce m_quota
reading. Another possibility is to
have a maximum number of delta_cells
*/
T const & operator[](unsigned i) const {
lean_assert(i < size());
cell const * it = m_ptr;
unsigned cost = 0;
while (true) {
switch (it->kind()) {
case cell_kind::PushBack:
if (i + 1 == to_push(it).m_size)
if (i + 1 == to_push(it).m_size) {
const_cast<pvector*>(this)->update_quota_on_read(cost);
return to_push(it).m_val;
}
break;
case cell_kind::PopBack:
break;
case cell_kind::Set:
if (to_set(it).m_idx == i)
if (to_set(it).m_idx == i) {
const_cast<pvector*>(this)->update_quota_on_read(cost);
return to_set(it).m_val;
}
break;
case cell_kind::Root:
const_cast<pvector*>(this)->update_quota_on_read(cost);
return to_root(it).m_vector[i];
}
it = static_cast<delta_cell const *>(it)->m_prev;
cost++;
}
}