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authorRich Felker <dalias@aerifal.cx>2012-12-10 18:31:39 -0500
committerRich Felker <dalias@aerifal.cx>2012-12-10 18:31:39 -0500
commitf1c1a5ea8295a3f8e9ea2db8961c5a68e1a3f9ed (patch)
tree496c245eda3bdbb12f9cb2520e58c22735034180 /src/stdio
parentbaf246e559e915a78a9703e10d15020c7edee423 (diff)
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document self-synchronized destruction issue for stdio locking
Diffstat (limited to 'src/stdio')
-rw-r--r--src/stdio/__lockfile.c10
1 files changed, 10 insertions, 0 deletions
diff --git a/src/stdio/__lockfile.c b/src/stdio/__lockfile.c
index 3bf3c26b..9d967d6e 100644
--- a/src/stdio/__lockfile.c
+++ b/src/stdio/__lockfile.c
@@ -14,5 +14,15 @@ int __lockfile(FILE *f)
 void __unlockfile(FILE *f)
 {
 	a_store(&f->lock, 0);
+
+	/* The following read is technically invalid under situations
+	 * of self-synchronized destruction. Another thread may have
+	 * called fclose as soon as the above store has completed.
+	 * Nonetheless, since FILE objects always live in memory
+	 * obtained by malloc from the heap, it's safe to assume
+	 * the dereferences below will not fault. In the worst case,
+	 * a spurious syscall will be made. If the implementation of
+	 * malloc changes, this assumption needs revisiting. */
+
 	if (f->waiters) __wake(&f->lock, 1, 1);
 }