Add a per session mutex, there are now things we do in parallel

which will need this.

We may need to improve MPL or LCK to cope with this.

bin/varnishd/cache/cache.h

@@ -709,6 +709,7 @@ struct sess {
 #define SESS_MAGIC		0x2c2f9c5a
 
 	enum sess_step		sess_step;
+	struct lock		mtx;
 	int			fd;
 	enum sess_close		reason;
 	uint32_t		vxid;

bin/varnishd/cache/cache_session.c

@@ -102,6 +102,7 @@ ses_setup(struct sess *sp)
 	sp->sockaddr.ss_family = sp->mysockaddr.ss_family = PF_UNSPEC;
 	sp->t_open = NAN;
 	sp->t_idle = NAN;
+	Lck_New(&sp->mtx, lck_sess);
 }
 
 /*--------------------------------------------------------------------
@@ -332,6 +333,7 @@ SES_Delete(struct sess *sp, enum sess_close reason, double now)
 	    b->pipe, b->pass, b->fetch, b->hdrbytes, b->bodybytes);
 	VSL(SLT_End, sp->vxid, "%s", "");
 
+	Lck_Delete(&sp->mtx);
 	MPL_Free(pp->mpl_sess, sp);
 }
 

include/tbl/locks.h

@@ -37,6 +37,7 @@ LOCK(hcb)
 LOCK(hcl)
 LOCK(vcl)
 LOCK(sessmem)
+LOCK(sess)
 LOCK(wstat)
 LOCK(herder)
 LOCK(wq)