Introduced ngx_rwlock_downgrade().

src/core/ngx_rwlock.c

diff --git a/src/core/ngx_rwlock.c b/src/core/ngx_rwlock.c
index 0aed29a..ed2b0f8 100644
--- a/src/core/ngx_rwlock.c
+++ b/src/core/ngx_rwlock.c
@@ -109,6 +109,15 @@
 }
 
 
+void
+ngx_rwlock_downgrade(ngx_atomic_t *lock)
+{
+    if (*lock == NGX_RWLOCK_WLOCK) {
+        *lock = 1;
+    }
+}
+
+
 #else
 
 #if (NGX_HTTP_UPSTREAM_ZONE || NGX_STREAM_UPSTREAM_ZONE)

src/core/ngx_rwlock.h

diff --git a/src/core/ngx_rwlock.h b/src/core/ngx_rwlock.h
index 8b16eca..41b42aa 100644
--- a/src/core/ngx_rwlock.h
+++ b/src/core/ngx_rwlock.h
@@ -16,6 +16,7 @@
 void ngx_rwlock_wlock(ngx_atomic_t *lock);
 void ngx_rwlock_rlock(ngx_atomic_t *lock);
 void ngx_rwlock_unlock(ngx_atomic_t *lock);
+void ngx_rwlock_downgrade(ngx_atomic_t *lock);
 
 
 #endif /* _NGX_RWLOCK_H_INCLUDED_ */