Fixup race condition in ub_cancel. For 1.3.0.

git-svn-id: file:///svn/unbound/trunk@1451 be551aaa-1e26-0410-a405-d3ace91eadb9

configure

@@ -1945,7 +1945,7 @@ LIBUNBOUND_AGE=0
 # 1.1.1 had 0:16:0
 # 1.2.0 had 0:17:0
 # 1.2.1 had 0:18:0
-# 1.3.0 had 0:19:0
+# 1.3.0 had 1:0:1
 
 #   Current  -- the number of the binary API that we're implementing
 #   Revision -- which iteration of the implementation of the binary

configure.ac

@@ -14,7 +14,7 @@ LIBUNBOUND_AGE=0
 # 1.1.1 had 0:16:0
 # 1.2.0 had 0:17:0
 # 1.2.1 had 0:18:0
-# 1.3.0 had 0:19:0
+# 1.3.0 had 1:0:1
 
 #   Current  -- the number of the binary API that we're implementing
 #   Revision -- which iteration of the implementation of the binary

doc/Changelog

@@ -1,5 +1,12 @@
 5 February 2009: Wouter
 	- ldns 1.5.0 rc as tarball included.
+	- 1.3.0 development continues:
+	  change in libunbound API: ub_cancel can return an error, that
+	  the async_id did not exist, or that it was already delivered.
+	  The result could have been delivered just before the cancel 
+	  routine managed to acquire the lock, so a caller may get the
+	  result at the same time they call cancel.  For this case, 
+	  ub_cancel tries to return an error code.
 
 4 February 2009: Wouter
 	- tag for release 1.2.1.

doc/libunbound.3.in

@@ -281,7 +281,8 @@ The async_id is returned so you can (at your option) decide to track it
 and cancel the request if needed.
 .TP
 .B ub_cancel
-Cancel an async query in progress.
+Cancel an async query in progress.  This may return an error if the query
+does not exist, or was already delivered.
 .TP
 .B ub_resolve_free
 Free struct ub_result contents after use.

libunbound/context.h

@@ -184,7 +184,9 @@ enum ub_ctx_err {
 	/** error in pipe communication with async bg worker */
 	UB_PIPE = -8,
 	/** error reading from file (resolv.conf) */
-	UB_READFILE = -9
+	UB_READFILE = -9,
+	/** error async_id does not exist or result already been delivered */
+	UB_NOID = -10
 };
 
 /**

libunbound/libunbound.c

@@ -642,7 +642,7 @@ ub_cancel(struct ub_ctx* ctx, int async_id)
 	if(!q || !q->async) {
 		/* it is not there, so nothing to do */
 		lock_basic_unlock(&ctx->cfglock);
-		return UB_NOERROR;
+		return UB_NOID;
 	}
 	log_assert(q->async);
 	q->cancelled = 1;
@@ -703,6 +703,7 @@ ub_strerror(int err)
 		case UB_AFTERFINAL: return "setting change after finalize";
 		case UB_PIPE: return "error in pipe communication with async";
 		case UB_READFILE: return "error reading file";
+		case UB_NOID: return "error async_id does not exist";
 		default: return "unknown error";
 	}
 }

libunbound/unbound.h

@@ -449,6 +449,11 @@ int ub_resolve_async(struct ub_ctx* ctx, char* name, int rrtype,
  * @param ctx: context.
  * @param async_id: which query to cancel.
  * @return 0 if OK, else error.
+ * This routine can return an error if the async_id passed does not exist
+ * or has already been delivered. If another thread is processing results
+ * at the same time, the result may be delivered at the same time and the
+ * cancel fails with an error.  Also the cancel can fail due to a system
+ * error, no memory or socket failures.
  */
 int ub_cancel(struct ub_ctx* ctx, int async_id);
 

testcode/asynclook.c

@@ -42,6 +42,7 @@
 
 #include "config.h"
 #include "libunbound/unbound.h"
+#include "libunbound/context.h"
 #include "util/locks.h"
 #include "util/log.h"
 
@@ -301,6 +302,7 @@ ext_thread(void* arg)
 				r = ub_cancel(inf->ctx, async_ids[i-100].id);
 				async_ids[i-100].cancel=1;
 				lock_basic_unlock(&async_ids[i-100].lock);
+				if(r != UB_NOID) 
 					checkerr("ub_cancel", r);
 			}
 		} else if(inf->thread_num > NUMTHR/2) {
@@ -467,6 +469,7 @@ int main(int argc, char** argv)
 		for(i=0; i<argc; i++) {
 			fprintf(stderr, "cancel %s\n", argv[i]);
 			r = ub_cancel(ctx, lookups[i].async_id);
+			if(r != UB_NOID) 
 				checkerr("ub_cancel", r);
 		}
 		num_wait = 0;