new file mode 100644
--- /dev/null
+++ b/src/http/ngx_http_busy_lock.h
@@ -0,0 +1,53 @@
+
+/*
+ * Copyright (C) Igor Sysoev
+ */
+
+
+#ifndef _NGX_HTTP_BUSY_LOCK_H_INCLUDED_
+#define _NGX_HTTP_BUSY_LOCK_H_INCLUDED_
+
+
+#include <ngx_config.h>
+#include <ngx_core.h>
+#include <ngx_event.h>
+#include <ngx_http.h>
+
+
+typedef struct {
+    u_char             *md5_mask;
+    char               *md5;
+    int                 cachable;
+
+    int                 busy;
+    int                 max_busy;
+
+    int                 waiting;
+    int                 max_waiting;
+
+    time_t              timeout;
+
+    ngx_event_mutex_t  *mutex;
+} ngx_http_busy_lock_t;
+
+
+typedef struct {
+    time_t         time;
+    ngx_event_t   *event;
+    void         (*event_handler)(ngx_event_t *ev);
+    u_char        *md5;
+    int            slot;
+} ngx_http_busy_lock_ctx_t;
+
+
+int ngx_http_busy_lock(ngx_http_busy_lock_t *bl, ngx_http_busy_lock_ctx_t *bc);
+int ngx_http_busy_lock_cachable(ngx_http_busy_lock_t *bl,
+                                ngx_http_busy_lock_ctx_t *bc, int lock);
+void ngx_http_busy_unlock(ngx_http_busy_lock_t *bl,
+                          ngx_http_busy_lock_ctx_t *bc);
+
+char *ngx_http_set_busy_lock_slot(ngx_conf_t *cf, ngx_command_t *cmd,
+                                  void *conf);
+
+
+#endif /* _NGX_HTTP_BUSY_LOCK_H_INCLUDED_ */