From 63078a04984b73e1fdeb4571a63605ee5c13f929 Mon Sep 17 00:00:00 2001 From: Tom Tromey Date: Tue, 13 Dec 2022 12:03:34 -0700 Subject: Avoid submitting empty tasks in parallel_for_each I found that parallel_for_each would submit empty tasks to the thread pool. For example, this can happen if the number of tasks is smaller than the number of available threads. In the DWARF reader, this resulted in the cooked index containing empty sub-indices. This patch arranges to instead shrink the result vector and process the trailing entries in the calling thread. --- gdb/unittests/parallel-for-selftests.c | 39 ++++++++++++++++++++++++++++++++++ 1 file changed, 39 insertions(+) (limited to 'gdb/unittests') diff --git a/gdb/unittests/parallel-for-selftests.c b/gdb/unittests/parallel-for-selftests.c index 3162db1..15a095a 100644 --- a/gdb/unittests/parallel-for-selftests.c +++ b/gdb/unittests/parallel-for-selftests.c @@ -149,6 +149,45 @@ TEST (int n_threads) SELF_CHECK (counter == NUMBER); #undef NUMBER + + /* Check that if there are fewer tasks than threads, then we won't + end up with a null result. */ + std::vector> intresults; + std::atomic any_empty_tasks (false); + + FOR_EACH (1, 0, 1, + [&] (int start, int end) + { + if (start == end) + any_empty_tasks = true; + return std::unique_ptr (new int (end - start)); + }); + SELF_CHECK (!any_empty_tasks); + SELF_CHECK (std::all_of (intresults.begin (), + intresults.end (), + [] (const std::unique_ptr &entry) + { + return entry != nullptr; + })); + + /* The same but using the task size parameter. */ + intresults.clear (); + any_empty_tasks = false; + FOR_EACH (1, 0, 1, + [&] (int start, int end) + { + if (start == end) + any_empty_tasks = true; + return std::unique_ptr (new int (end - start)); + }, + task_size_one); + SELF_CHECK (!any_empty_tasks); + SELF_CHECK (std::all_of (intresults.begin (), + intresults.end (), + [] (const std::unique_ptr &entry) + { + return entry != nullptr; + })); } #endif /* FOR_EACH */ -- cgit v1.1