[clangd] Trace time the operations wait on Semaphore.
The Semaphore is currently used to limit the number of concurrently
running tasks. Tracing the wait times will allow to find out how much
time is wasted waiting on other operations to complete.
git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@334495 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/clangd/Threading.cpp b/clangd/Threading.cpp
index 2220611..dfd0d2e 100644
--- a/clangd/Threading.cpp
+++ b/clangd/Threading.cpp
@@ -1,4 +1,5 @@
#include "Threading.h"
+#include "Trace.h"
#include "llvm/ADT/ScopeExit.h"
#include "llvm/Support/FormatVariadic.h"
#include "llvm/Support/Threading.h"
@@ -23,9 +24,14 @@
Semaphore::Semaphore(std::size_t MaxLocks) : FreeSlots(MaxLocks) {}
void Semaphore::lock() {
- std::unique_lock<std::mutex> Lock(Mutex);
- SlotsChanged.wait(Lock, [&]() { return FreeSlots > 0; });
- --FreeSlots;
+ trace::Span Span("WaitForFreeSemaphoreSlot");
+ // trace::Span can also acquire locks in ctor and dtor, we make sure it
+ // happens when Semaphore's own lock is not held.
+ {
+ std::unique_lock<std::mutex> Lock(Mutex);
+ SlotsChanged.wait(Lock, [&]() { return FreeSlots > 0; });
+ --FreeSlots;
+ }
}
void Semaphore::unlock() {
