Add mdb_reader_list()

Dump the active slots in the reader table.

libraries/liblmdb/lmdb.h

@@ -1298,6 +1298,23 @@ int  mdb_cmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b);
 	 * @return < 0 if a < b, 0 if a == b, > 0 if a > b
 	 */
 int  mdb_dcmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b);
+
+	/** @brief A callback function used to print a message from the library.
+	 *
+	 * @param[in] msg The string to be printed.
+	 * @param[in] ctx An arbitrary context pointer for the callback.
+	 * @return < 0 on failure, 0 on success.
+	 */
+typedef int (MDB_msg_func)(const char *msg, void *ctx);
+
+	/** @brief Dump the entries in the reader lock table.
+	 *
+	 * @param[in] env An environment handle returned by #mdb_env_create()
+	 * @param[in] func A #MDB_msg_func function
+	 * @param[in] ctx Anything the message function needs
+	 * @return < 0 on failure, 0 on success.
+	 */
+int	mdb_reader_list(MDB_env *env, MDB_msg_func *func, void *ctx);
 /**	@} */
 
 #ifdef __cplusplus

libraries/liblmdb/mdb.c

@@ -7916,4 +7916,39 @@ int mdb_set_relctx(MDB_txn *txn, MDB_dbi dbi, void *ctx)
 	return MDB_SUCCESS;
 }
 
+int mdb_reader_list(MDB_env *env, MDB_msg_func *func, void *ctx)
+{
+	unsigned int i, rdrs;
+	MDB_reader *mr;
+	char buf[128];
+	int first = 1;
+
+	if (!env || !func)
+		return -1;
+	if (!env->me_txns) {
+		return func("No reader locks\n", ctx);
+	}
+	rdrs = env->me_numreaders;
+	mr = env->me_txns->mti_readers;
+	for (i=0; i<rdrs; i++) {
+		if (mr[i].mr_pid) {
+			size_t tid;
+			int rc;
+			tid = mr[i].mr_tid;
+			if (mr[i].mr_txnid == (txnid_t)-1) {
+				sprintf(buf, "%10d %zx -\n", mr[i].mr_pid, tid);
+			} else {
+				sprintf(buf, "%10d %zx %zu\n", mr[i].mr_pid, tid, mr[i].mr_txnid);
+			}
+			if (first) {
+				first = 0;
+				func("    pid     thread     txnid\n", ctx);
+			}
+			rc = func(buf, ctx);
+			if (rc < 0)
+				return rc;
+		}
+	}
+	return 0;
+}
 /** @} */

libraries/liblmdb/mdb_stat.1

@@ -13,6 +13,8 @@ mdb_stat \- LMDB environment status tool
 [\c
 .BR \-n ]
 [\c
+.BR \-r ]
+[\c
 .BR \-a \ |
 .BI \-s \ subdb\fR]
 .SH DESCRIPTION
@@ -32,6 +34,13 @@ If \fB\-fff\fP is given, display the full list of page IDs in the freelist.
 .BR \-n
 Display the status of an LMDB database which does not use subdirectories.
 .TP
+.BR \-r
+Display information about the environment reader table.
+Shows the process ID, thread ID, and transaction ID for each active
+reader slot. The process ID and transaction ID are in decimal, the
+thread ID is in hexadecimal. The transaction ID is displayed as "-"
+if the reader does not currently have a read transaction open.
+.TP
 .BR \-a
 Display the status of all of the subdatabases in the environment.
 .TP

libraries/liblmdb/mdb_stat.c

@@ -31,7 +31,7 @@ static void prstat(MDB_stat *ms)
 
 static void usage(char *prog)
 {
-	fprintf(stderr, "usage: %s dbpath [-e] [-f[f[f]]] [-n] [-a|-s subdb]\n", prog);
+	fprintf(stderr, "usage: %s dbpath [-e] [-f[f[f]]] [-n] [-a|-s subdb] [-r]\n", prog);
 	exit(EXIT_FAILURE);
 }
 
@@ -46,7 +46,7 @@ int main(int argc, char *argv[])
 	char *prog = argv[0];
 	char *envname;
 	char *subname = NULL;
-	int alldbs = 0, envinfo = 0, envflags = 0, freinfo = 0;
+	int alldbs = 0, envinfo = 0, envflags = 0, freinfo = 0, rdrinfo = 0;
 
 	if (argc < 2) {
 		usage(prog);
@@ -59,7 +59,7 @@ int main(int argc, char *argv[])
 	 * -n: use NOSUBDIR flag on env_open
 	 * (default) print stat of only the main DB
 	 */
-	while ((i = getopt(argc, argv, "aefns:")) != EOF) {
+	while ((i = getopt(argc, argv, "aefnrs:")) != EOF) {
 		switch(i) {
 		case 'a':
 			if (subname)
@@ -75,6 +75,9 @@ int main(int argc, char *argv[])
 		case 'n':
 			envflags |= MDB_NOSUBDIR;
 			break;
+		case 'r':
+			rdrinfo++;
+			break;
 		case 's':
 			if (alldbs)
 				usage(prog);
@@ -120,6 +123,11 @@ int main(int argc, char *argv[])
 		printf("  Number of readers used: %u\n", mei.me_numreaders);
 	}
 
+	if (rdrinfo) {
+		printf("Reader Table Status\n");
+		rc = mdb_reader_list(env, (MDB_msg_func *)fputs, stdout);
+	}
+
 	if (freinfo) {
 		MDB_cursor *cursor;
 		MDB_val key, data;