Visible to Intel only — GUID: GUID-614E69FB-29FA-4146-AAD6-4F12835AB85A
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
Waiting for Single Messages in Flow Graph
Visible to Intel only — GUID: GUID-614E69FB-29FA-4146-AAD6-4F12835AB85A
Avoiding Data Races
The edges in a flow graph make explicit the dependence relationships that you want the library to enforce. Similarly, the concurrency limits on function_node and multifunction_node objects limit the maximum number of concurrent invocations that the runtime library will allow. These are the limits that are enforced by the library; the library does not automatically protect you from data races. You must explicitly prevent data races by using these mechanisms.
For example, the follow code has a data race because there is nothing to prevent concurrent accesses to the global count object referenced by node f:
graph g;
int src_count = 1;
int global_sum = 0;
int limit = 100000;
input_node< int > src( g, [&]( oneapi::tbb::flow_control& fc ) -> int {
if ( src_count <= limit ) {
return src_count++;
} else {
fc.stop();
return int();
}
} );
src.activate();
function_node< int, int > f( g, unlimited, [&]( int i ) -> int {
global_sum += i; // data race on global_sum
return i;
} );
make_edge( src, f );
g.wait_for_all();
cout << "global sum = " << global_sum
<< " and closed form = " << limit*(limit+1)/2 << "\n";If you run the above example, it will likely calculate a global sum that is a bit smaller than the expected solution due to the data race. The data race could be avoided in this simple example by changing the allowed concurrency in f from unlimited to 1, forcing each value to be processed sequentially by f. You may also note that the input_node also updates a global value, src_count. However, since an input_node always executes serially, there is no race possible.