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lock-like protection for update_exact 

The exact choice of memory_order_* is hard, and even for versions that
seem to work on x86_64 TSAN complains like crazy.

TODO: a version that, instead of blocking if another thread is updating,
also does the computation, with suitable protection to ensure that
pruning the tree cannot happen while anyone is computing on it.

TODO: try having AT in Lazy instead of Lazy_rep (i.e. not shared) to
avoid the indirection. We can possibly choose one or the other depending
on the type.
This commit is contained in:
Marc Glisse 2020-11-13 01:03:57 +01:00
parent ba054d51c2
commit bf0a42d740
3 changed files with 174 additions and 117 deletions
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216
Filtered_kernel/include/CGAL/Lazy.h
View File

@ -53,6 +53,7 @@
#include <utility>
#include <vector>
#include <atomic>
#include <thread>
namespace CGAL {
@ -65,10 +66,10 @@ struct Indirect_AT {
Indirect_AT():p(new AT()){}
Indirect_AT(AT const& a):p(new AT(a)){}
Indirect_AT(AT&& a):p(new AT(std::move(a))){}
Indirect_AT& operator=(AT const& a){ old.reset(p.load(std::memory_order_relaxed)); p.store(new AT(a), std::memory_order_relaxed); return *this; }
Indirect_AT& operator=(AT&& a){ old.reset(p.load(std::memory_order_relaxed)); p.store(new AT(std::move(a)), std::memory_order_relaxed); return *this; }
operator AT const&()const{return *p.load(std::memory_order_relaxed);}
~Indirect_AT() { delete p.load(std::memory_order_relaxed); }
Indirect_AT& operator=(AT const& a){ old.reset(p.load(std::memory_order_relaxed)); p.store(new AT(a), std::memory_order_release); return *this; }
Indirect_AT& operator=(AT&& a){ old.reset(p.load(std::memory_order_relaxed)); p.store(new AT(std::move(a)), std::memory_order_release); return *this; }
operator AT const&()const{return *p.load(std::memory_order_acquire);}
~Indirect_AT() { delete p.load(std::memory_order_acquire); }
};
template <class E,
@ -90,18 +91,6 @@ approx(const Lazy<AT,ET,E2A>& l)
return l.approx();
}
#if 0
// Where is this one (non-const) needed ? Is it ?
template <typename AT, typename ET, typename E2A>
inline
AT&
approx(Lazy<AT,ET,E2A>& l)
{
return l.approx();
}
#endif
template <typename AT, typename ET, typename E2A>
inline
const ET&
@ -259,8 +248,8 @@ public:
typedef AT_ AT;
mutable Indirect_AT<AT> at;
mutable std::atomic<ET*> et;
mutable Indirect_AT<AT> at{};
mutable std::atomic<ET*> et { nullptr };
Lazy_rep ()
: at(), et(nullptr){}
@ -283,6 +272,69 @@ public:
return at;
}
#if 1
#define CGAL_UPDATE_EXACT_BEGIN \
if (!this->start_update()) return;
#define CGAL_UPDATE_EXACT_MIDDLE \
this->et.store(pet, std::memory_order_release);
#define CGAL_UPDATE_EXACT_END
// true if you should update
bool start_update() const
{
ET* other = nullptr;
// TODO specify memory_order_*
bool doit = et.compare_exchange_strong(other, (ET*)1);
if (!doit) {
// Wait until it becomes available
while ((uintptr_t)other == 1) {
std::this_thread::yield(); // or do nothing?
other = et.load(std::memory_order_relaxed);
}
return false;
}
return true;
}
const ET & exact() const
{
uintptr_t pet = (uintptr_t) et.load(std::memory_order_relaxed);
if (pet <= 1) {
if (pet == 0)
update_exact();
else
// Wait until it becomes available
while((uintptr_t)et.load(std::memory_order_relaxed)==1)
std::this_thread::yield(); // or do nothing?
}
return *et.load(std::memory_order_consume);
// Should we return the pointer from update_exact, to avoid an extra load and synchronization?
}
#elif 1
mutable std::atomic<std::thread::id> worker{}; // thread that is allowed to updatee
#define CGAL_UPDATE_EXACT_BEGIN \
if (!this->start_update()) return;
#define CGAL_UPDATE_EXACT_MIDDLE \
this->et.store(pet, std::memory_order_release);
#define CGAL_UPDATE_EXACT_END
// true if you should update
bool start_update() const
{
std::thread::id none{};
// TODO specify memory_order_*
bool doit = worker.compare_exchange_strong(none, std::this_thread::get_id());
if (!doit) {
// Wait until it becomes available
while(et.load(std::memory_order_relaxed)==nullptr)
std::this_thread::yield(); // or do nothing?
return false;
}
return true;
}
const ET & exact() const
{
if (et.load(std::memory_order_relaxed)==nullptr)
@ -291,20 +343,53 @@ public:
// Should we return the pointer from update_exact, to avoid an extra load and synchronization?
}
// ??? Is this needed? Safe?
ET & exact()
{
if (et.load(std::memory_order_relaxed)==nullptr)
update_exact();
return *et.load(std::memory_order_consume);
#else
mutable std::atomic_uint workers{}; // number of threads running update_exact
// not written yet
#define CGAL_UPDATE_EXACT_BEGIN \
workers.fetch_add(1, std::memory_order_relaxed); \
if (et.load(std::memory_order_relaxed)!=nullptr) \
if (!this->start_update()) return;
#define CGAL_UPDATE_EXACT_MIDDLE \
bool updated = this->set_exact(pet); \
if (!updated) { /* some other thread was faster */ \
pet->~ET(); \
} else if (this->end_update()) {
#define CGAL_UPDATE_EXACT_END \
}
bool set_exact(ET* pet) const
{
ET* other = nullptr;
return this->et.compare_exchange_strong(other, pet, std::memory_order_release);
}
// true if you should update
bool start_update() const
{
unsigned int w = workers.fetch_add(1, std::memory_order_relaxed);
???
}
// true if you are the last one and can clean-up
bool end_update() const
{
bool b = workers.load(std::memory_order_relaxed) == 1
|| workers.fetch_sub(1, std::memory_order_release) == 1;
// unneeded for Lazy_rep_0?
if(b) std::atomic_thread_fence(std::memory_order_acquire);
return b;
}
const ET & exact() const
{
if (et.load(std::memory_order_relaxed)==nullptr)
update_exact();
return *et.load(std::memory_order_consume);
// Should we return the pointer from update_exact, to avoid an extra load and synchronization?
}
#endif
#ifdef CGAL_LAZY_KERNEL_DEBUG
void print_at_et(std::ostream& os, int level) const
{
@ -350,14 +435,12 @@ class Lazy_rep_n :
const EC& ec() const { return *this; }
template<std::size_t...I>
void update_exact_helper(std::index_sequence<I...>) const {
ET* pet = new ET(ec()( CGAL::exact( std::get<I>(l) ) ... ) );
bool updated = this->set_exact(pet);
if (!updated) { // some other thread was faster
pet->~ET();
} else {
CGAL_UPDATE_EXACT_BEGIN
ET* pet = new ET(ec()( CGAL::exact( std::get<I>(l) ) ... ) );
CGAL_UPDATE_EXACT_MIDDLE
this->at = E2A()(*pet);
l = std::tuple<L...>{};
}
CGAL_UPDATE_EXACT_END
}
public:
void update_exact() const {
@ -403,11 +486,10 @@ public:
void
update_exact() const
{
ET* pet = new ET();
bool updated = this->set_exact(pet);
if (!updated) {
pet->~ET();
}
CGAL_UPDATE_EXACT_BEGIN
ET* pet = new ET();
CGAL_UPDATE_EXACT_MIDDLE
CGAL_UPDATE_EXACT_END
}
Lazy_rep_0()
@ -518,19 +600,17 @@ public:
void
update_exact() const
{
ET* pet = new ET();
CGAL_UPDATE_EXACT_BEGIN
ET* pet = new ET();
// TODO : This looks really unfinished...
std::vector<Object> vec;
//this->et->reserve(this->at.size());
ec()(CGAL::exact(l1_), std::back_inserter(pet));
bool updated = this->set_exact(pet);
if (!updated) {
pet->~ET();
} else {
std::vector<Object> vec;
//this->et->reserve(this->at.size());
ec()(CGAL::exact(l1_), std::back_inserter(*pet));
CGAL_UPDATE_EXACT_MIDDLE
this->at = E2A()(*pet);
// Prune lazy tree
l1_ = L1();
}
CGAL_UPDATE_EXACT_END
}
Lazy_rep_with_vector_1(const AC& ac, const EC& /*ec*/, const L1& l1)
@ -574,18 +654,16 @@ public:
void
update_exact() const
{
ET* pet = new ET();
pet->reserve(this->at.size());
ec()(CGAL::exact(l1_), CGAL::exact(l2_), std::back_inserter(pet));
bool updated = this->set_exact(pet);
if (!updated) {
pet->~ET();
} else {
CGAL_UPDATE_EXACT_BEGIN
ET* pet = new ET();
pet->reserve(this->at.size());
ec()(CGAL::exact(l1_), CGAL::exact(l2_), std::back_inserter(*pet));
CGAL_UPDATE_EXACT_MIDDLE
this->at = E2A()(*pet);
// Prune lazy tree
l1_ = L1();
l2_ = L2();
}
CGAL_UPDATE_EXACT_END
}
Lazy_rep_with_vector_2(const AC& ac, const EC& /*ec*/, const L1& l1, const L2& l2)
@ -629,17 +707,15 @@ public:
void
update_exact() const
{
ET* pet = new ET();
ec()(CGAL::exact(l1_), CGAL::exact(l2_), pet);
bool updated = this->set_exact(pet);
if (!updated) {
pet->~ET();
} else {
CGAL_UPDATE_EXACT_BEGIN
ET* pet = new ET();
ec()(CGAL::exact(l1_), CGAL::exact(l2_), *pet);
CGAL_UPDATE_EXACT_MIDDLE
this->at = E2A()(*pet);
// Prune lazy tree
l1_ = L1();
l2_ = L2();
}
CGAL_UPDATE_EXACT_END
}
Lazy_rep_2_1(const AC& ac, const EC& /*ec*/, const L1& l1, const L2& l2)
@ -686,17 +762,15 @@ public:
void
update_exact() const
{
ET* pet = new ET();
ec()(CGAL::exact(l1_), CGAL::exact(l2_), pet->first, pet->second );
bool updated = this->set_exact(pet);
if (!updated) {
pet->~ET();
} else {
CGAL_UPDATE_EXACT_BEGIN
ET* pet = new ET();
ec()(CGAL::exact(l1_), CGAL::exact(l2_), pet->first, pet->second );
CGAL_UPDATE_EXACT_MIDDLE
this->at = E2A()(*pet);
// Prune lazy tree
l1_ = L1();
l2_ = L2();
}
CGAL_UPDATE_EXACT_END
}
Lazy_rep_2_2(const AC& ac, const EC& /*ec*/, const L1& l1, const L2& l2)
@ -799,14 +873,6 @@ public :
const ET& exact() const
{ return ptr()->exact(); }
#if 0
AT& approx()
{ return ptr()->approx(); }
#endif
ET& exact()
{ return ptr()->exact(); }
unsigned depth() const
{
return ptr()->depth();

68
Number_types/include/CGAL/Lazy_exact_nt.h
View File

@ -130,11 +130,10 @@ struct Lazy_exact_Int_Cst : public Lazy_exact_nt_rep<ET>
: Lazy_exact_nt_rep<ET>(double(i)) {}
void update_exact() const {
ET* pet = new ET((int)this->approx().inf());
bool updated = this->set_exact(pet);
if (!updated) {
pet->~ET();
}
CGAL_UPDATE_EXACT_BEGIN
ET* pet = new ET((int)this->approx().inf());
CGAL_UPDATE_EXACT_MIDDLE
CGAL_UPDATE_EXACT_END
}
};
@ -146,11 +145,10 @@ struct Lazy_exact_Cst : public Lazy_exact_nt_rep<ET>
: Lazy_exact_nt_rep<ET>(x), cste(x) {}
void update_exact() const {
ET* pet = new ET(cste);
bool updated = this->set_exact(pet);
if (!updated) {
pet->~ET();
}
CGAL_UPDATE_EXACT_BEGIN
ET* pet = new ET(cste);
CGAL_UPDATE_EXACT_MIDDLE
CGAL_UPDATE_EXACT_END
}
private:
@ -191,14 +189,12 @@ public:
void update_exact() const
{
ET* pet = new ET(l.exact());
bool updated = this->set_exact(pet);
if (!updated) {
pet->~ET();
} else {
CGAL_UPDATE_EXACT_BEGIN
ET* pet = new ET(l.exact());
CGAL_UPDATE_EXACT_MIDDLE
this->at = l.approx();
prune_dag();
}
CGAL_UPDATE_EXACT_END
}
void prune_dag() const { l.reset(); }
@ -284,15 +280,13 @@ struct NAME : public Lazy_exact_unary<ET> \
\
void update_exact() const \
{ \
ET* pet = new ET(OP(this->op1.exact())); \
bool updated = this->set_exact(pet); \
if (!updated) { \
pet->~ET(); \
} else { \
CGAL_UPDATE_EXACT_BEGIN \
ET* pet = new ET(OP(this->op1.exact())); \
CGAL_UPDATE_EXACT_MIDDLE \
if (!this->approx().is_point()) \
this->at = CGAL_NTS to_interval(*(this->et)); \
this->prune_dag(); \
} \
CGAL_UPDATE_EXACT_END \
} \
};
@ -312,15 +306,13 @@ struct NAME : public Lazy_exact_binary<ET, ET1, ET2> \
\
void update_exact() const \
{ \
ET* pet = new ET(this->op1.exact() OP this->op2.exact()); \
bool updated = this->set_exact(pet); \
if (!updated) { \
pet->~ET(); \
} else { \
CGAL_UPDATE_EXACT_BEGIN \
ET* pet = new ET(this->op1.exact() OP this->op2.exact()); \
CGAL_UPDATE_EXACT_MIDDLE \
if (!this->approx().is_point()) \
this->at = CGAL_NTS to_interval(*(this->et)); \
this->prune_dag(); \
} \
CGAL_UPDATE_EXACT_END \
} \
};
@ -338,15 +330,13 @@ struct Lazy_exact_Min : public Lazy_exact_binary<ET>
void update_exact() const
{
ET* pet = new ET((CGAL::min)(this->op1.exact(), this->op2.exact()));
bool updated = this->set_exact(pet);
if (!updated) {
pet->~ET();
} else {
CGAL_UPDATE_EXACT_BEGIN
ET* pet = new ET((CGAL::min)(this->op1.exact(), this->op2.exact()));
CGAL_UPDATE_EXACT_MIDDLE
if (!this->approx().is_point())
this->at = CGAL_NTS to_interval(*(this->et));
this->prune_dag();
}
CGAL_UPDATE_EXACT_END
}
};
@ -359,15 +349,13 @@ struct Lazy_exact_Max : public Lazy_exact_binary<ET>
void update_exact() const
{
ET* pet = new ET((CGAL::max)(this->op1.exact(), this->op2.exact()));
bool updated = this->set_exact(pet);
if (!updated) {
pet->~ET();
} else {
CGAL_UPDATE_EXACT_BEGIN
ET* pet = new ET((CGAL::max)(this->op1.exact(), this->op2.exact()));
CGAL_UPDATE_EXACT_MIDDLE
if (!this->approx().is_point())
this->at = CGAL_NTS to_interval(*(this->et));
this->prune_dag();
}
CGAL_UPDATE_EXACT_END
}
};

7
STL_Extension/include/CGAL/Handle.h
View File

@ -79,11 +79,14 @@ class Handle
{
if (PTR)
{
// TODO: the first condition tries to avoid the expensive
// release synchronization, check that it is still safe.
// The advanced version seems to work in practice on x86_64, but TSAN complains like crazy, even if I remove the questionable first test.
#if 0
if (PTR->count.load(std::memory_order_relaxed) == 1
|| PTR->count.fetch_sub(1, std::memory_order_release) == 1) {
std::atomic_thread_fence(std::memory_order_acquire);
#else
if (PTR->count.fetch_sub(1, std::memory_order_acq_rel) == 1) {
#endif
delete PTR;
}
PTR=0;