Visible to Intel only — GUID: GUID-AE01E995-1C5D-4ED8-8807-2210B156653B
Package Contents
Parallelizing Simple Loops
Parallelizing Complex Loops
Parallelizing Data Flow and Dependence Graphs
Work Isolation
Exceptions and Cancellation
Containers
Mutual Exclusion
Timing
Memory Allocation
The Task Scheduler
Design Patterns
Migrating from Threading Building Blocks (TBB)
Constrained APIs
Invoke a Callable Object
Appendix A Costs of Time Slicing
Appendix B Mixing With Other Threading Packages
References
parallel_for_each Body semantics and requirements
parallel_sort ranges interface extension
TBB_malloc_replacement_log Function
Parallel Reduction for rvalues
Type-specified message keys for join_node
Scalable Memory Pools
Helper Functions for Expressing Graphs
concurrent_lru_cache
task_group extensions
The customizing mutex type for concurrent_hash_map
Description
API
Visible to Intel only — GUID: GUID-AE01E995-1C5D-4ED8-8807-2210B156653B
The customizing mutex type for concurrent_hash_map
NOTE:
To enable this feature, define the TBB_PREVIEW_CONCURRENT_HASH_MAP_EXTENSIONS macro to 1.
Description
oneTBB concurrnent_hash_map class uses reader-writer mutex to provide thread safety and avoid data races for insert, lookup, and erasure operations. This feature adds an extra template parameter for concurrent_hash_map that allows to customize the type of the reader-writer mutex.
API
Header
#include <oneapi/tbb/concurrent_hash_map.h>
Synopsis
namespace oneapi {
namespace tbb {
template <typename Key, typename T,
typename HashCompare = tbb_hash_compare<Key>,
typename Allocator = tbb_allocator<std::pair<const Key, T>>,
typename Mutex = spin_rw_mutex>
class concurrent_hash_map {
using mutex_type = Mutex;
};
} // namespace tbb
} // namespace oneapi
Type requirements
The type of the mutex passed as a template argument for concurrent_hash_map should meet the requirements of ReaderWriterMutex. It should also provide the following API:
boolReaderWriterMutex::scoped_lock::is_writer()const;
Returns: true if the scoped_lock object acquires the mutex as a writer, false otherwise.
The behavior is undefined if the scoped_lock object does not acquire the mutex.
oneapi::tbb::spin_rw_mutex, oneapi::tbb::speculative_spin_rw_mutex, oneapi::tbb::queuing_rw_mutex, oneapi::tbb::null_rw_mutex, and oneapi::tbb::rw_mutex meet the requirements above.
Example
The example below demonstrates how to wrap std::shared_mutex (C++17) to meet the requirements of ReaderWriterMutex and how to customize concurrent_hash_map to use this mutex.
#define TBB_PREVIEW_CONCURRENT_HASH_MAP_EXTENSIONS 1
#include "oneapi/tbb/concurrent_hash_map.h"
#include <shared_mutex>
class SharedMutexWrapper {
public:
// ReaderWriterMutex requirements
static constexpr bool is_rw_mutex = true;
static constexpr bool is_recursive_mutex = false;
static constexpr bool is_fair_mutex = false;
class scoped_lock {
public:
scoped_lock() : my_mutex_ptr(nullptr), my_writer_flag(false) {}
scoped_lock(SharedMutexWrapper& mutex, bool write = true)
: my_mutex_ptr(&mutex), my_writer_flag(write)
{
if (my_writer_flag) {
my_mutex_ptr->my_mutex.lock();
} else {
my_mutex_ptr->my_mutex.lock_shared();
}
}
~scoped_lock() {
if (my_mutex_ptr) release();
}
void acquire(SharedMutexWrapper& mutex, bool write = true) {
if (my_mutex_ptr) release();
my_mutex_ptr = &mutex;
my_writer_flag = write;
if (my_writer_flag) {
my_mutex_ptr->my_mutex.lock();
} else {
my_mutex_ptr->my_mutex.lock_shared();
}
}
void release() {
if (my_writer_flag) {
my_mutex_ptr->my_mutex.unlock();
} else {
my_mutex_ptr->my_mutex.unlock_shared();
}
}
bool upgrade_to_writer() {
// std::shared_mutex does not have the upgrade/downgrade parallel_for_each_semantics
if (my_writer_flag) return true; // Already a writer
my_mutex_ptr->my_mutex.unlock_shared();
my_mutex_ptr->my_mutex.lock();
return false; // The lock was reacquired
}
bool downgrade_to_reader() {
if (!my_writer_flag) return true; // Already a reader
my_mutex_ptr->my_mutex.unlock();
my_mutex_ptr->my_mutex.lock_shared();
return false;
}
bool is_writer() const {
return my_writer_flag;
}
private:
SharedMutexWrapper* my_mutex_ptr;
bool my_writer_flag;
};
private:
std::shared_mutex my_mutex;
}; // struct SharedMutexWrapper
int main() {
using map_type = oneapi::tbb::concurrent_hash_map<int, int,
oneapi::tbb::tbb_hash_compare<int>,
oneapi::tbb::tbb_allocator<std::pair<const int, int>>,
SharedMutexWrapper>;
map_type map; // This object will use SharedMutexWrapper for thread safety of insert/find/erase operations
}