#include <deal.II/base/template_constraints.h>
#include <deal.II/base/std_cxx1x/function.h>
#include <deal.II/base/std_cxx1x/bind.h>
+#include <deal.II/base/thread_local_storage.h>
#ifdef DEAL_II_WITH_THREADS
# include <deal.II/base/thread_management.h>
# include <tbb/pipeline.h>
+# include <thread>
#endif
#include <vector>
#include <utility>
+#include <memory>
DEAL_II_NAMESPACE_OPEN
#ifdef DEAL_II_WITH_THREADS
-
namespace internal
{
+
+//TODO: The following classes all use std_cxx1x::shared_ptr, but the
+// correct pointer class would actually be std::unique_ptr. make this
+// replacement whenever we have a class that provides these semantics
+// and that is available also as a fall-back whenever via boost or similar
+
/**
* A class that creates a sequence of
* items from a range of iterators.
public:
/**
* A data type that we use to identify
- * items to be worked on.
- *
- * The first element indicates an array
- * of iterators to work on; the second
- * the scratch space; the third an
- * array of copy data spaces; and the
- * last the number of elements to work
- * on. This last argument is an integer
- * between one and chunk_size. The
- * arrays have a length of chunk_size.
+ * items to be worked on. This is the structure
+ * that is passed around between the different parts of
+ * the WorkStream implementation to identify what needs
+ * to be done by the various stages of the pipeline.
*/
- typedef
- std_cxx1x::tuple<std::vector<Iterator>,
- ScratchData *,
- std::vector<CopyData>,
- unsigned int>
- ItemType;
+ struct ItemType
+ {
+ /**
+ * A structure that contains a pointer to a scratch data object along
+ * with a flag that indicates whether this object is currently in use.
+ */
+ struct ScratchDataObject
+ {
+ std_cxx1x::shared_ptr<ScratchData> scratch_data;
+ bool currently_in_use;
+ };
+
+ /**
+ * Typedef to a list of scratch data objects. The rationale for this
+ * list is provided in the variables that use these lists.
+ */
+ typedef std::list<ScratchDataObject> ScratchDataList;
+
+ /**
+ * A list of iterators that need to be worked on. Only the first
+ * n_items are relevant.
+ */
+ std::vector<Iterator> work_items;
+
+ /**
+ * The CopyData objects that the Worker part of the pipeline
+ * fills for each work item. Again, only the first n_items
+ * elements are what we care about.
+ */
+ std::vector<CopyData> copy_datas;
+
+ /**
+ * Number of items identified by the work_items array that the
+ * Worker and Copier pipeline stage need to work on. The maximum
+ * value of this variable will be chunk_size.
+ */
+ unsigned int n_items;
+
+ /**
+ * Pointer to a thread local variable identifying the scratch data objects
+ * this thread will use. The initial implementation of this
+ * class using thread local variables provided only a single
+ * scratch object per thread. This doesn't work, because
+ * the worker functions may start tasks itself and then call
+ * Threads::TaskGroup::join_all() or a similar function, which the
+ * TBB scheduler may use to run something else on the current
+ * thread -- for example another instance of the worker function.
+ * Consequently, there would be two instances of the worker
+ * function that use the same scratch object if we only
+ * provided a single scratch object per thread. The solution is
+ * to provide a list of scratch objects for each thread, together
+ * with a flag indicating whether this scratch object is currently
+ * used. If a thread needs a scratch object, it walks this list
+ * until it finds an unused object, or, if there is none, creates one
+ * itself. Note that we need not use synchronization primitives
+ * for this process since the lists are thread-local and
+ * we are guaranteed that only a single thread accesses them as long
+ * as we have no yield point in between the accesses to the list.
+ *
+ * The pointers to scratch objects stored in each of these lists must
+ * be so that they are deleted on all threads when the thread
+ * local object is destroyed. This is achieved by using shared_ptr.
+ *
+ * Note that when a worker needs to create a scratch object, it allocates
+ * it using sample_scratch_data to copy from. This has
+ * the advantage of a first-touch initialization, i.e., the
+ * memory for the scratch data object is allocated and initialized
+ * by the same thread that will later use it.
+ */
+ Threads::ThreadLocalStorage<ScratchDataList> *scratch_data;
+
+ /**
+ * Pointer to a sample scratch data object, to be used to initialize
+ * the scratch data objects created for each individual thread.
+ */
+ const ScratchData *sample_scratch_data;
+ };
/**
tbb::filter (/*is_serial=*/true),
remaining_iterator_range (begin, end),
ring_buffer (buffer_size),
+ sample_scratch_data (sample_scratch_data),
n_emitted_items (0),
chunk_size (chunk_size)
{
tasks += Threads::new_task (&IteratorRangeToItemStream::init_buffer_elements,
*this,
i,
- std_cxx1x::cref(sample_scratch_data),
std_cxx1x::cref(sample_copy_data));
tasks.join_all ();
}
- /**
- * Destructor.
- */
- ~IteratorRangeToItemStream ()
- {
- for (unsigned int i=0; i<ring_buffer.size(); ++i)
- delete std_cxx1x::get<1>(ring_buffer[i]);
- }
-
/**
* Create a item and return a
* pointer to it.
// initialize the next item. it may
// consist of at most chunk_size
// elements
- std_cxx1x::get<3>(*current_item) = 0;
+ current_item->n_items = 0;
while ((remaining_iterator_range.first !=
remaining_iterator_range.second)
&&
- (std_cxx1x::get<3>(*current_item) < chunk_size))
+ (current_item->n_items < chunk_size))
{
- std_cxx1x::get<0>(*current_item)[std_cxx1x::get<3>(*current_item)]
+ current_item->work_items[current_item->n_items]
= remaining_iterator_range.first;
++remaining_iterator_range.first;
- ++std_cxx1x::get<3>(*current_item);
+ ++current_item->n_items;
}
- if (std_cxx1x::get<3>(*current_item) == 0)
+ if (current_item->n_items == 0)
// there were no items
// left. terminate the pipeline
return 0;
*/
std::vector<ItemType> ring_buffer;
+ /**
+ * Pointer to a thread local variable identifying the scratch data objects
+ * this thread will use. The initial implementation of this
+ * class using thread local variables provided only a single
+ * scratch object per thread. This doesn't work, because
+ * the worker functions may start tasks itself and then call
+ * Threads::TaskGroup::join_all() or a similar function, which the
+ * TBB scheduler may use to run something else on the current
+ * thread -- for example another instance of the worker function.
+ * Consequently, there would be two instances of the worker
+ * function that use the same scratch object if we only
+ * provided a single scratch object per thread. The solution is
+ * to provide a list of scratch objects for each thread, together
+ * with a flag indicating whether this scratch object is currently
+ * used. If a thread needs a scratch object, it walks this list
+ * until it finds an unused object, or, if there is none, creates one
+ * itself. Note that we need not use synchronization primitives
+ * for this process since the lists are thread-local and
+ * we are guaranteed that only a single thread accesses them as long
+ * as we have no yield point in between the accesses to the list.
+ *
+ * The pointers to scratch objects stored in each of these lists must
+ * be so that they are deleted on all threads when the thread
+ * local object is destroyed. This is achieved by using shared_ptr.
+ *
+ * Note that when a worker needs to create a scratch object, it allocates
+ * it using sample_scratch_data to copy from. This has
+ * the advantage of a first-touch initialization, i.e., the
+ * memory for the scratch data object is allocated and initialized
+ * by the same thread that will later use it.
+ */
+ Threads::ThreadLocalStorage<typename ItemType::ScratchDataList> thread_local_scratch;
+
+ /**
+ * A reference to a sample scratch data that will be used to
+ * initialize the thread-local pointers to a scratch data object
+ * each of the worker tasks uses.
+ */
+ const ScratchData &sample_scratch_data;
+
/**
* Counter for the number of emitted
* items. Each item may consist of up
* to chunk_size iterator elements.
*/
- unsigned int n_emitted_items;
+ unsigned int n_emitted_items;
/**
* Number of elements of the
* the ring buffer.
*/
void init_buffer_elements (const unsigned int element,
- const ScratchData &sample_scratch_data,
const CopyData &sample_copy_data)
{
- Assert (std_cxx1x::get<1>(ring_buffer[element]) == 0,
+ Assert (ring_buffer[element].n_items == 0,
ExcInternalError());
- std_cxx1x::get<0>(ring_buffer[element])
+ ring_buffer[element].work_items
.resize (chunk_size, remaining_iterator_range.second);
- std_cxx1x::get<1>(ring_buffer[element])
- = new ScratchData(sample_scratch_data);
- std_cxx1x::get<2>(ring_buffer[element])
+ ring_buffer[element].scratch_data
+ = &thread_local_scratch;
+ ring_buffer[element].sample_scratch_data
+ = &sample_scratch_data;
+ ring_buffer[element].copy_datas
.resize (chunk_size, sample_copy_data);
}
};
ItemType *current_item = static_cast<ItemType *> (item);
+ // we need to find an unused scratch data object in the list that
+ // corresponds to the current thread and then mark it as used. if
+ // we can't find one, create one
+ //
+ // as discussed in the discussion of the documentation of the
+ // IteratorRangeToItemStream::scratch_data variable, there is no
+ // need to synchronize access to this variable using a mutex
+ // as long as we have no yield-point in between. this means that
+ // we can't take an iterator into the list now and expect it to
+ // still be valid after calling the worker, but we at least do
+ // not have to lock the following section
+ ScratchData *scratch_data = 0;
+ {
+ typename ItemType::ScratchDataList &
+ scratch_data_list = current_item->scratch_data->get();
+
+ // see if there is an unused object. if so, grab it and mark
+ // it as used
+ for (typename ItemType::ScratchDataList::iterator
+ p = scratch_data_list.begin();
+ p != scratch_data_list.end(); ++p)
+ if (p->currently_in_use == false)
+ {
+ scratch_data = p->scratch_data.get();
+ p->currently_in_use = true;
+ break;
+ }
+
+ // if no object was found, create one and mark it as used
+ if (scratch_data == 0)
+ {
+ scratch_data = new ScratchData(*current_item->sample_scratch_data);
+
+ typename ItemType::ScratchDataList::value_type
+ new_scratch_object = { std::shared_ptr<ScratchData>(scratch_data), true };
+ scratch_data_list.push_back (new_scratch_object);
+ }
+ }
+
// then call the worker function on each element of the chunk we were
// given. since these worker functions are called on separate threads,
// nothing good can happen if they throw an exception and we are best
// off catching it and showing an error message
- for (unsigned int i=0; i<std_cxx1x::get<3>(*current_item); ++i)
+ for (unsigned int i=0; i<current_item->n_items; ++i)
{
try
{
- worker (std_cxx1x::get<0>(*current_item)[i],
- *std_cxx1x::get<1>(*current_item),
- std_cxx1x::get<2>(*current_item)[i]);
+ worker (current_item->work_items[i],
+ *scratch_data,
+ current_item->copy_datas[i]);
}
catch (const std::exception &exc)
{
}
}
+ // finally mark the scratch object as unused again. as above, there
+ // is no need to lock anything here since the object we work on
+ // is thread-local
+ {
+ typename ItemType::ScratchDataList &
+ scratch_data_list = current_item->scratch_data->get();
+
+ for (typename ItemType::ScratchDataList::iterator p =
+ scratch_data_list.begin(); p != scratch_data_list.end();
+ ++p)
+ if (p->scratch_data.get() == scratch_data)
+ {
+ Assert(p->currently_in_use == true, ExcInternalError());
+ p->currently_in_use = false;
+ }
+ }
+
+
+
// then return the original pointer
// to the now modified object
return item;
// initiate copying data. for the same reasons as in the worker class
// above, catch exceptions rather than letting it propagate into
// unknown territories
- for (unsigned int i=0; i<std_cxx1x::get<3>(*current_item); ++i)
+ for (unsigned int i=0; i<current_item->n_items; ++i)
{
try
{
- copier (std_cxx1x::get<2>(*current_item)[i]);
+ copier (current_item->copy_datas[i]);
}
catch (const std::exception &exc)
{
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