From ad8349b7e9f3a2e5ac9c8d48a940b2675b8a84e2 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Robert=20M=C3=BCller?= <robytemueller@gmail.com>
Date: Sat, 12 Oct 2024 10:28:00 +0200
Subject: [PATCH] Avoid busy waiting in `CHttpRequest::Wait` function

Use a condition variable instead of busy waiting until HTTP requests are done.

Also set the state `EHttpState::RUNNING` which was previously unused.

Closes #7811.
---
 src/engine/shared/http.cpp | 17 ++++++-----------
 src/engine/shared/http.h   |  2 ++
 2 files changed, 8 insertions(+), 11 deletions(-)

diff --git a/src/engine/shared/http.cpp b/src/engine/shared/http.cpp
index c69da07dcda..d308abab80b 100644
--- a/src/engine/shared/http.cpp
+++ b/src/engine/shared/http.cpp
@@ -379,6 +379,7 @@ void CHttpRequest::OnCompletionInternal(void *pHandle, unsigned int Result)
 	// before the result has been initialized/updated in OnCompletion.
 	OnCompletion(State);
 	m_State = State;
+	m_WaitCondition.notify_all();
 }
 
 void CHttpRequest::WriteToFile(IStorage *pStorage, const char *pDest, int StorageType)
@@ -402,18 +403,11 @@ void CHttpRequest::Header(const char *pNameColonValue)
 
 void CHttpRequest::Wait()
 {
-	using namespace std::chrono_literals;
-
-	// This is so uncommon that polling just might work
-	for(;;)
-	{
+	std::unique_lock Lock(m_WaitMutex);
+	m_WaitCondition.wait(Lock, [this]() {
 		EHttpState State = m_State.load(std::memory_order_seq_cst);
-		if(State != EHttpState::QUEUED && State != EHttpState::RUNNING)
-		{
-			return;
-		}
-		std::this_thread::sleep_for(10ms);
-	}
+		return State != EHttpState::QUEUED && State != EHttpState::RUNNING;
+	});
 }
 
 void CHttpRequest::Result(unsigned char **ppResult, size_t *pResultLength) const
@@ -604,6 +598,7 @@ void CHttp::RunLoop()
 				goto error_configure;
 			}
 
+			pRequest->m_State = EHttpState::RUNNING;
 			m_RunningRequests.emplace(pEH, std::move(pRequest));
 			NewRequests.pop_front();
 			continue;
diff --git a/src/engine/shared/http.h b/src/engine/shared/http.h
index 86e53fac9fd..40bef7771fc 100644
--- a/src/engine/shared/http.h
+++ b/src/engine/shared/http.h
@@ -116,6 +116,8 @@ class CHttpRequest : public IHttpRequest
 	char m_aErr[256]; // 256 == CURL_ERROR_SIZE
 	std::atomic<EHttpState> m_State{EHttpState::QUEUED};
 	std::atomic<bool> m_Abort{false};
+	std::mutex m_WaitMutex;
+	std::condition_variable m_WaitCondition;
 
 	int m_StatusCode = 0;
 	bool m_HeadersEnded = false;