libutil: drop Pool resources on exceptional free

if a scope owning a resource does not gracefully drop that resource
while handling exceptions from deeper down the call stack we should
assume the resource is invalid state and drop it. currently it *is*
true that such cases do not cause resources to be freed, but thanks
to validator misuses this has so far not caused any larger problem.

Change-Id: Ie4f91bcd60a64d05c5ff9d22cc97954816d13b97
This commit is contained in:
eldritch horrors 2024-03-21 21:27:07 +01:00
parent 4b730f328e
commit 620de98d0c
2 changed files with 23 additions and 1 deletions

View file

@ -1,6 +1,7 @@
#pragma once #pragma once
///@file ///@file
#include <exception>
#include <functional> #include <functional>
#include <limits> #include <limits>
#include <list> #include <list>
@ -118,7 +119,7 @@ public:
if (!r) return; if (!r) return;
{ {
auto state_(pool.state.lock()); auto state_(pool.state.lock());
if (!bad) if (!bad && !std::uncaught_exceptions())
state_->idle.push_back(ref<R>(r)); state_->idle.push_back(ref<R>(r));
assert(state_->inUse); assert(state_->inUse);
state_->inUse--; state_->inUse--;
@ -134,6 +135,12 @@ public:
Handle get() Handle get()
{ {
// we do not want to handle the complexity that comes with allocating
// resources during stack unwinding. it would be possible to do this,
// but doing so requires more per-handle bookkeeping to properly free
// resources allocated during unwinding. that effort is not worth it.
assert(std::uncaught_exceptions() == 0);
{ {
auto state_(state.lock()); auto state_(state.lock());

View file

@ -124,4 +124,19 @@ namespace nix {
ASSERT_NE(h->num, counter); ASSERT_NE(h->num, counter);
} }
} }
TEST(Pool, throwingOperationDropsResource)
{
auto createResource = []() { return make_ref<TestResource>(); };
Pool<TestResource> pool = Pool<TestResource>((size_t)1, createResource);
ASSERT_THROW({
auto _r = pool.get();
ASSERT_EQ(pool.count(), 1);
throw 1;
}, int);
ASSERT_EQ(pool.count(), 0);
}
} }