[ThreadPool] add ability to group tasks into separate groups

This is needed for parallelizing of loading modules symbols in LLDB
(D122975). Currently LLDB can parallelize indexing symbols
when loading a module, but modules are loaded sequentially. If LLDB
index cache is enabled, this means that the cache loading is not
parallelized, even though it could. However doing that creates
a threadpool-within-threadpool situation, so the number of threads
would not be properly limited.

This change adds ThreadPoolTaskGroup as a simple type that can be
used with ThreadPool calls to put tasks into groups that can be
independently waited for (even recursively from within a task)
but still run in the same thread pool.

Differential Revision: https://reviews.llvm.org/D123225

1 files changed, 1 insertions, 0 deletions

diff --git a/llvm/tools/llvm-profdata/llvm-profdata.cpp b/llvm/tools/llvm-profdata/llvm-profdata.cpp
index ce5f0a8..aea6088 100644
--- a/llvm/tools/llvm-profdata/llvm-profdata.cpp
+++ b/llvm/tools/llvm-profdata/llvm-profdata.cpp
@@ -38,6 +38,7 @@
 #include "llvm/Support/WithColor.h"
 #include "llvm/Support/raw_ostream.h"
 #include <algorithm>
+#include <queue>
 
 using namespace llvm;