--- a/hotspot/src/share/vm/utilities/taskqueue.hpp Wed Aug 05 18:54:12 2009 -0700
+++ b/hotspot/src/share/vm/utilities/taskqueue.hpp Wed Aug 05 12:33:29 2009 -0700
@@ -22,94 +22,90 @@
*
*/
-#ifdef LP64
-typedef juint TAG_TYPE;
-// for a taskqueue size of 4M
-#define LOG_TASKQ_SIZE 22
-#else
-typedef jushort TAG_TYPE;
-// for a taskqueue size of 16K
-#define LOG_TASKQ_SIZE 14
-#endif
-
class TaskQueueSuper: public CHeapObj {
protected:
- // The first free element after the last one pushed (mod _n).
+ // Internal type for indexing the queue; also used for the tag.
+ typedef NOT_LP64(uint16_t) LP64_ONLY(uint32_t) idx_t;
+
+ // The first free element after the last one pushed (mod N).
volatile uint _bottom;
- // log2 of the size of the queue.
- enum SomeProtectedConstants {
- Log_n = LOG_TASKQ_SIZE
+ enum {
+ N = 1 << NOT_LP64(14) LP64_ONLY(17), // Queue size: 16K or 128K
+ MOD_N_MASK = N - 1 // To compute x mod N efficiently.
};
-#undef LOG_TASKQ_SIZE
+
+ class Age {
+ public:
+ Age(size_t data = 0) { _data = data; }
+ Age(const Age& age) { _data = age._data; }
+ Age(idx_t top, idx_t tag) { _fields._top = top; _fields._tag = tag; }
- // Size of the queue.
- uint n() { return (1 << Log_n); }
- // For computing "x mod n" efficiently.
- uint n_mod_mask() { return n() - 1; }
+ Age get() const volatile { return _data; }
+ void set(Age age) volatile { _data = age._data; }
+
+ idx_t top() const volatile { return _fields._top; }
+ idx_t tag() const volatile { return _fields._tag; }
- struct Age {
- TAG_TYPE _top;
- TAG_TYPE _tag;
+ // Increment top; if it wraps, increment tag also.
+ void increment() {
+ _fields._top = increment_index(_fields._top);
+ if (_fields._top == 0) ++_fields._tag;
+ }
- TAG_TYPE tag() const { return _tag; }
- TAG_TYPE top() const { return _top; }
+ Age cmpxchg(const Age new_age, const Age old_age) volatile {
+ return (size_t) Atomic::cmpxchg_ptr((intptr_t)new_age._data,
+ (volatile intptr_t *)&_data,
+ (intptr_t)old_age._data);
+ }
+
+ bool operator ==(const Age& other) const { return _data == other._data; }
- Age() { _tag = 0; _top = 0; }
-
- friend bool operator ==(const Age& a1, const Age& a2) {
- return a1.tag() == a2.tag() && a1.top() == a2.top();
- }
+ private:
+ struct fields {
+ idx_t _top;
+ idx_t _tag;
+ };
+ union {
+ size_t _data;
+ fields _fields;
+ };
};
- Age _age;
- // These make sure we do single atomic reads and writes.
- Age get_age() {
- uint res = *(volatile uint*)(&_age);
- return *(Age*)(&res);
+
+ volatile Age _age;
+
+ // These both operate mod N.
+ static uint increment_index(uint ind) {
+ return (ind + 1) & MOD_N_MASK;
}
- void set_age(Age a) {
- *(volatile uint*)(&_age) = *(uint*)(&a);
+ static uint decrement_index(uint ind) {
+ return (ind - 1) & MOD_N_MASK;
}
- TAG_TYPE get_top() {
- return get_age().top();
- }
-
- // These both operate mod _n.
- uint increment_index(uint ind) {
- return (ind + 1) & n_mod_mask();
- }
- uint decrement_index(uint ind) {
- return (ind - 1) & n_mod_mask();
- }
-
- // Returns a number in the range [0.._n). If the result is "n-1", it
- // should be interpreted as 0.
+ // Returns a number in the range [0..N). If the result is "N-1", it should be
+ // interpreted as 0.
uint dirty_size(uint bot, uint top) {
- return ((int)bot - (int)top) & n_mod_mask();
+ return (bot - top) & MOD_N_MASK;
}
// Returns the size corresponding to the given "bot" and "top".
uint size(uint bot, uint top) {
uint sz = dirty_size(bot, top);
- // Has the queue "wrapped", so that bottom is less than top?
- // There's a complicated special case here. A pair of threads could
- // perform pop_local and pop_global operations concurrently, starting
- // from a state in which _bottom == _top+1. The pop_local could
- // succeed in decrementing _bottom, and the pop_global in incrementing
- // _top (in which case the pop_global will be awarded the contested
- // queue element.) The resulting state must be interpreted as an empty
- // queue. (We only need to worry about one such event: only the queue
- // owner performs pop_local's, and several concurrent threads
- // attempting to perform the pop_global will all perform the same CAS,
- // and only one can succeed. Any stealing thread that reads after
- // either the increment or decrement will see an empty queue, and will
- // not join the competitors. The "sz == -1 || sz == _n-1" state will
- // not be modified by concurrent queues, so the owner thread can reset
- // the state to _bottom == top so subsequent pushes will be performed
- // normally.
- if (sz == (n()-1)) return 0;
- else return sz;
+ // Has the queue "wrapped", so that bottom is less than top? There's a
+ // complicated special case here. A pair of threads could perform pop_local
+ // and pop_global operations concurrently, starting from a state in which
+ // _bottom == _top+1. The pop_local could succeed in decrementing _bottom,
+ // and the pop_global in incrementing _top (in which case the pop_global
+ // will be awarded the contested queue element.) The resulting state must
+ // be interpreted as an empty queue. (We only need to worry about one such
+ // event: only the queue owner performs pop_local's, and several concurrent
+ // threads attempting to perform the pop_global will all perform the same
+ // CAS, and only one can succeed.) Any stealing thread that reads after
+ // either the increment or decrement will see an empty queue, and will not
+ // join the competitors. The "sz == -1 || sz == N-1" state will not be
+ // modified by concurrent queues, so the owner thread can reset the state to
+ // _bottom == top so subsequent pushes will be performed normally.
+ return (sz == N - 1) ? 0 : sz;
}
public:
@@ -122,22 +118,21 @@
// The "careful" version admits the possibility of pop_local/pop_global
// races.
uint size() {
- return size(_bottom, get_top());
+ return size(_bottom, _age.top());
}
uint dirty_size() {
- return dirty_size(_bottom, get_top());
+ return dirty_size(_bottom, _age.top());
}
void set_empty() {
_bottom = 0;
- _age = Age();
+ _age.set(0);
}
// Maximum number of elements allowed in the queue. This is two less
// than the actual queue size, for somewhat complicated reasons.
- uint max_elems() { return n() - 2; }
-
+ uint max_elems() { return N - 2; }
};
template<class E> class GenericTaskQueue: public TaskQueueSuper {
@@ -179,12 +174,12 @@
template<class E>
GenericTaskQueue<E>::GenericTaskQueue():TaskQueueSuper() {
- assert(sizeof(Age) == sizeof(int), "Depends on this.");
+ assert(sizeof(Age) == sizeof(size_t), "Depends on this.");
}
template<class E>
void GenericTaskQueue<E>::initialize() {
- _elems = NEW_C_HEAP_ARRAY(E, n());
+ _elems = NEW_C_HEAP_ARRAY(E, N);
guarantee(_elems != NULL, "Allocation failed.");
}
@@ -208,14 +203,14 @@
template<class E>
bool GenericTaskQueue<E>::push_slow(E t, uint dirty_n_elems) {
- if (dirty_n_elems == n() - 1) {
+ if (dirty_n_elems == N - 1) {
// Actually means 0, so do the push.
uint localBot = _bottom;
_elems[localBot] = t;
_bottom = increment_index(localBot);
return true;
- } else
- return false;
+ }
+ return false;
}
template<class E>
@@ -230,53 +225,45 @@
// then have the owner thread do a pop followed by another push. Without
// the incrementing of "tag", the pop_global's CAS could succeed,
// allowing it to believe it has claimed the stale element.)
- Age newAge;
- newAge._top = localBot;
- newAge._tag = oldAge.tag() + 1;
+ Age newAge((idx_t)localBot, oldAge.tag() + 1);
// Perhaps a competing pop_global has already incremented "top", in which
// case it wins the element.
if (localBot == oldAge.top()) {
- Age tempAge;
// No competing pop_global has yet incremented "top"; we'll try to
// install new_age, thus claiming the element.
- assert(sizeof(Age) == sizeof(int), "Assumption about CAS unit.");
- *(uint*)&tempAge = Atomic::cmpxchg(*(uint*)&newAge, (volatile uint*)&_age, *(uint*)&oldAge);
+ Age tempAge = _age.cmpxchg(newAge, oldAge);
if (tempAge == oldAge) {
// We win.
- assert(dirty_size(localBot, get_top()) != n() - 1,
- "Shouldn't be possible...");
+ assert(dirty_size(localBot, _age.top()) != N - 1, "sanity");
return true;
}
}
- // We fail; a completing pop_global gets the element. But the queue is
- // empty (and top is greater than bottom.) Fix this representation of
- // the empty queue to become the canonical one.
- set_age(newAge);
- assert(dirty_size(localBot, get_top()) != n() - 1,
- "Shouldn't be possible...");
+ // We lose; a completing pop_global gets the element. But the queue is empty
+ // and top is greater than bottom. Fix this representation of the empty queue
+ // to become the canonical one.
+ _age.set(newAge);
+ assert(dirty_size(localBot, _age.top()) != N - 1, "sanity");
return false;
}
template<class E>
bool GenericTaskQueue<E>::pop_global(E& t) {
- Age newAge;
- Age oldAge = get_age();
+ Age oldAge = _age.get();
uint localBot = _bottom;
uint n_elems = size(localBot, oldAge.top());
if (n_elems == 0) {
return false;
}
+
t = _elems[oldAge.top()];
- newAge = oldAge;
- newAge._top = increment_index(newAge.top());
- if ( newAge._top == 0 ) newAge._tag++;
- Age resAge;
- *(uint*)&resAge = Atomic::cmpxchg(*(uint*)&newAge, (volatile uint*)&_age, *(uint*)&oldAge);
+ Age newAge(oldAge);
+ newAge.increment();
+ Age resAge = _age.cmpxchg(newAge, oldAge);
+
// Note that using "_bottom" here might fail, since a pop_local might
// have decremented it.
- assert(dirty_size(localBot, newAge._top) != n() - 1,
- "Shouldn't be possible...");
- return (resAge == oldAge);
+ assert(dirty_size(localBot, newAge.top()) != N - 1, "sanity");
+ return resAge == oldAge;
}
template<class E>
@@ -459,7 +446,7 @@
return offer_termination(NULL);
}
- // As above, but it also terminates of the should_exit_termination()
+ // As above, but it also terminates if the should_exit_termination()
// method of the terminator parameter returns true. If terminator is
// NULL, then it is ignored.
bool offer_termination(TerminatorTerminator* terminator);
@@ -492,11 +479,10 @@
}
#else
uint localBot = _bottom;
- assert((localBot >= 0) && (localBot < n()), "_bottom out of range.");
- TAG_TYPE top = get_top();
+ assert((localBot >= 0) && (localBot < N), "_bottom out of range.");
+ idx_t top = _age.top();
uint dirty_n_elems = dirty_size(localBot, top);
- assert((dirty_n_elems >= 0) && (dirty_n_elems < n()),
- "n_elems out of range.");
+ assert((dirty_n_elems >= 0) && (dirty_n_elems < N), "n_elems out of range.");
if (dirty_n_elems < max_elems()) {
_elems[localBot] = t;
_bottom = increment_index(localBot);
@@ -517,12 +503,12 @@
return true;
#else
uint localBot = _bottom;
- // This value cannot be n-1. That can only occur as a result of
+ // This value cannot be N-1. That can only occur as a result of
// the assignment to bottom in this method. If it does, this method
// resets the size( to 0 before the next call (which is sequential,
// since this is pop_local.)
- uint dirty_n_elems = dirty_size(localBot, get_top());
- assert(dirty_n_elems != n() - 1, "Shouldn't be possible...");
+ uint dirty_n_elems = dirty_size(localBot, _age.top());
+ assert(dirty_n_elems != N - 1, "Shouldn't be possible...");
if (dirty_n_elems == 0) return false;
localBot = decrement_index(localBot);
_bottom = localBot;
@@ -534,15 +520,14 @@
// If there's still at least one element in the queue, based on the
// "_bottom" and "age" we've read, then there can be no interference with
// a "pop_global" operation, and we're done.
- TAG_TYPE tp = get_top(); // XXX
+ idx_t tp = _age.top(); // XXX
if (size(localBot, tp) > 0) {
- assert(dirty_size(localBot, tp) != n() - 1,
- "Shouldn't be possible...");
+ assert(dirty_size(localBot, tp) != N - 1, "sanity");
return true;
} else {
// Otherwise, the queue contained exactly one element; we take the slow
// path.
- return pop_local_slow(localBot, get_age());
+ return pop_local_slow(localBot, _age.get());
}
#endif
}