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mobile/bind: fix a reference count race with the garbage collectors

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Each side of the language barrier maintains a map of reference numbers
to objects. Each entry has a reference count that exactly matches
the number of active proxy objects on the other side. When a reference
crosses the barrier, the count is incremented and when a proxy finalizer
is run, the count is decremented. If the count reaches 0, the reference
number and its object are removed from the map.

There is a possibility that a reference number is passed to the other
side, and the last proxy is then immediately garbage collected and
finalized. The reference counter then reaches 0 before the other side has
converted the reference number to its object, crashing the program.

This is possible in both Go/Java/ObjC but is most likely to happen in
ObjC because its own automatic reference count runtime frees objects
as soon as they are statically never referenced again.

Fix the race by always incrementing the reference count before sending
a reference across the barrier. When converting the reference back into
an object on the other side, decrement the counter again.

Only the new ObjC test fails without this fix, but I left the Java
counterpart in for good measure.

Change-Id: I92743aabec275b4a5b82b952052e7e284872ce02
Reviewed-on: https://go-review.googlesource.com/21311
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>
This commit is contained in:
Elias Naur
2016-03-30 18:24:55 +00:00
parent 5b96314b59
commit 07a529f836
18 changed files with 237 additions and 43 deletions
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bind/java/SeqTest.java
+13 -1
View File
@@ -502,8 +502,20 @@ public class SeqTest extends InstrumentationTestCase {
Secondpkg.Ser ser = Testpkg.NewSer();
}
public void testIDup() {
public void testRoundtripEquality() {
Testpkg.I want = new AnI();
assertTrue("java object passed through Go should not be wrapped", want == Testpkg.IDup(want));
Testpkg.InterfaceDupper idup = new Testpkg.InterfaceDupper.Stub(){
@Override public Testpkg.Interface IDup(Testpkg.Interface i) {
return i;
}
};
assertTrue("Go interface passed through Java should not be wrapped", Testpkg.CallIDupper(idup));
Testpkg.ConcreteDupper cdup = new Testpkg.ConcreteDupper.Stub(){
@Override public Testpkg.Concrete CDup(Testpkg.Concrete c) {
return c;
}
};
assertTrue("Go struct passed through Java should not be wrapped", Testpkg.CallCDupper(cdup));
}
}