From 615f227ff486aa64602cc3c5344af7185cc295f1 Mon Sep 17 00:00:00 2001
From: Florian Fischer <florian.fl.fischer@fau.de>
Date: Wed, 4 Nov 2020 13:39:36 +0100
Subject: [PATCH] initialize the blocked context pointer to prevent undefined
unblock
Not initializing blockedContext means its original value is undefined and
probably some random stack value != nullptr.
If the first put() is executed before the first blocking get(), put() will read a
random value from blockedContext and will call unblock with this random context
pointer leading to execution of random memory.
---
emper/UnboundedBlockingMpscQueue.hpp | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/emper/UnboundedBlockingMpscQueue.hpp b/emper/UnboundedBlockingMpscQueue.hpp
index c28449ab..47dd19f6 100644
--- a/emper/UnboundedBlockingMpscQueue.hpp
+++ b/emper/UnboundedBlockingMpscQueue.hpp
@@ -11,7 +11,7 @@ class UnboundedBlockingMpscQueue : protected Logger<LogSubsystem::U_B_MPSC_Q>
, protected Blockable {
private:
- std::atomic<Context*> blockedContext;
+ std::atomic<Context*> blockedContext = nullptr;
bool tPopped;
T t;
@@ -27,6 +27,10 @@ private:
}
void tryToGetElement(std::function<void(void)> postRetrieve) {
+ // tPopped indicates that 't' is a popped and usable value.
+ // Therefore if we tryToGet a new 't' while 't' is available the current 't'
+ // would be overridden and dropped.
+ assert(!tPopped);
std::lock_guard<std::mutex> lock(queueMutex);
if (!mpscQueue.empty()) {
t = mpscQueue.front();
--
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