+/**
+ * VCL Locked Sessions (VLS) is a wrapper that synchronizes access to VCL APIs
+ * which are, by construction, not thread safe. To this end, VLS uses
+ * configuration and heuristics to detect how applications use sessions in
+ * an attempt to optimize the locking strategy. The modes of operation
+ * currently supported are the following:
+ *
+ * 1) per-process workers
+ *
+ * +----------+ +----------+
+ * | | | |
+ * | process0 | | process1 |
+ * | | | |
+ * +-----+----+ +-----+----+
+ * | |
+ * | |
+ * +-----+----+ +-----+----+
+ * | | | |
+ * | vls_wrk0 | | vls_wrk1 |
+ * | | | |
+ * +-----+----+ +-----+----+
+ * | |
+ * | |
+ * +-----+----+ +-----+----+
+ * | | | |
+ * | vcl_wrk0 | | vcl_wrk1 |
+ * | | | |
+ * +----------+ +----------+
+ *
+ * 2) per-thread workers 3) single-worker multi-thread
+ *
+ * +---------+ +---------+ +---------+ +---------+
+ * | | | | | | | |
+ * | thread0 | | thread1 | | thread0 | | thread1 |
+ * | | | | | | | |
+ * +--------++ +-+-------+ +--------++ +-+-------+
+ * | | | |
+ * | | | |
+ * +-+------+-+ +-+------+-+
+ * | | | |
+ * | vls_wrk0 | | vls_wrk0 |
+ * | | | |
+ * +-+------+-+ +----+-----+
+ * | | |
+ * | | |
+ * +--------+-+ +-+--------+ +----+-----+
+ * | | | | | |
+ * | vcl_wrk0 | | vcl_wrk1 | | vcl_wrk0 |
+ * | | | | | |
+ * +----------+ +----------+ +----------+
+ *
+ * 1) per-process workers: intercept fork calls and assume all children
+ * processes are new workers that must be registered with vcl. VLS
+ * sessions are cloned and shared between workers. Only shared sessions
+ * are locked on use and thereby only one process can interact with
+ * them at a time (explicit sharing).
+ *
+ * 2) per-thread workers: each newly detected pthread is assumed to be a new
+ * worker and is registered with vcl. Enabled via configuration.
+ * When a thread tries to access a session it does not own, a clone and
+ * share rpc request is sent to the owning thread via vcl and vpp.
+ * Consequently, a vls session can map to multiple vcl sessions, one per
+ * vcl worker. VLS sessions are locked on use (implicit sharing).
+ *
+ * 3) single-worker multi-thread: vls does not make any assumptions about
+ * application threads and therefore implements an aggressive locking
+ * strategy that limits access to underlying vcl resources based on type
+ * of interaction and locks vls session on use (implicit sharing).
+ */
+