Codegen C - Fix Box drop impl not being overridden

1 files changed, 22 insertions, 0 deletions

diff --git a/Notes/BugStories.txt b/Notes/BugStories.txt
index 0e2ca1dd..b7437fb6 100644
--- a/Notes/BugStories.txt
+++ b/Notes/BugStories.txt
@@ -22,5 +22,27 @@ librustc takes ~20mins to recompile, and that's just one crate out of ~80 in rus
 - Enable optimisation debug and rebuild libcore
 - Oh look, `sizeof<*const T>` where `T: ?Sized` is returning 16 instead of returning "I don't know yet"
 
+
+2019-07-20: Leaking MPSC handles
+================================
+
+- rustc just stopping after codegen
+- gdb backtrace shows only one thread, waiting on a MPSC receiver
+- add debugging for MPSC Shared handles for that specific type, LOOTS of them being made (testing on a 14 core machine)
+- Turn down codegen units to 1, now a total of 6 handles (much easier)
+- Check all allocation paths, looks like all of them should call the destructor on the returned handle...
+  - One path hands a handle to a thread, let's chase that down
+  - Nope... that destuctor does get called... hmm...
+- Break down (after two weekends) and hack in handle indexes to mpsc::Shared
+  (on clone, allocate a unique ID and store that in the handle).
+- Re-run, printing the handle indexes - Notice that one code path (two
+  handles) leaks its handles
+- Re-check, the destructor is called... but I can't break on it?
+- Chase down the call chain, reach a Box drop impl (wait... that exists, I
+  thought the compiler made a custom one)
+  - It does absolutely nothing. No free, no destructor... oops
+- Turns out that 1.29 added a no-op Drop impl for Box (1.19 didn't have one), which
+  caused mrustc's magic Drop impl to not be created.
+
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