--- a/src/imap-hibernate/imap-client.c	Tue Aug 02 13:41:07 2016 +0300
+++ b/src/imap-hibernate/imap-client.c	Tue Jul 19 10:16:17 2016 -0600
@@ -11,6 +11,7 @@
 #include "istream.h"
 #include "ostream.h"
 #include "llist.h"
+#include "priorityq.h"
 #include "base64.h"
 #include "str.h"
 #include "strescape.h"
@@ -28,6 +29,16 @@
 /* we only need enough for "DONE\r\nIDLE\r\n" */
 #define IMAP_MAX_INBUF 12
 
+/* If client has sent input and we can't recreate imap process in this
+   many seconds, disconnect the client. */
+#define IMAP_CLIENT_MOVE_BACK_WITH_INPUT_TIMEOUT_SECS 10
+/* If there's a change notification and we can't recreate imap process in this
+   many seconds, disconnect the client. */
+#define IMAP_CLIENT_MOVE_BACK_WITHOUT_INPUT_TIMEOUT_SECS (60*5)
+
+/* How often to try to unhibernate clients. */
+#define IMAP_UNHIBERNATE_RETRY_MSECS 10
+
 enum imap_client_input_state {
 	IMAP_CLIENT_INPUT_STATE_UNKNOWN,
 	IMAP_CLIENT_INPUT_STATE_BAD,
@@ -42,11 +53,16 @@
 };
 
 struct imap_client {
+	struct priorityq_item item;
+
 	struct imap_client *prev, *next;
 	pool_t pool;
 	struct imap_client_state state;
 	ARRAY(struct imap_client_notify) notifys;
 
+	time_t move_back_start;
+	struct timeout *to_move_back;
+
 	int fd;
 	struct io *io;
 	struct istream *input;
@@ -57,14 +73,19 @@
 	unsigned int imap_still_here_text_pos;
 	unsigned int next_read_threshold;
 	bool bad_done, idle_done;
+	bool unhibernate_queued;
+	bool input_pending;
 };
 
 static struct imap_client *imap_clients;
+static struct priorityq *unhibernate_queue;
+static struct timeout *to_unhibernate;
 static const char imap_still_here_text[] = "* OK Still here\r\n";
 
 static void imap_client_stop(struct imap_client *client);
 void imap_client_destroy(struct imap_client **_client, const char *reason);
 static void imap_client_add_idle_keepalive_timeout(struct imap_client *client);
+static void imap_clients_unhibernate(void *context);
 
 static void imap_client_disconnected(struct imap_client **_client)
 {
@@ -174,22 +195,53 @@
 	}
 }
 
-static void imap_client_move_back(struct imap_client *client)
+static bool imap_client_try_move_back(struct imap_client *client)
 {
 	const struct master_service_settings *master_set;
-	const char *path;
-
-	imap_client_stop(client);
+	const char *path, *error;
+	int ret;
 
 	master_set = master_service_settings_get(master_service);
 	path = t_strconcat(master_set->base_dir,
 			   "/"IMAP_MASTER_SOCKET_NAME, NULL);
-	if (imap_master_connection_init(path,
-					imap_client_move_back_send_callback,
-					imap_client_move_back_read_callback,
-					client, &client->master_conn) < 0) {
+	ret = imap_master_connection_init(path,
+					  imap_client_move_back_send_callback,
+					  imap_client_move_back_read_callback,
+					  client, &client->master_conn, &error);
+	if (ret > 0) {
+		/* success */
+		imap_client_stop(client);
+		return TRUE;
+	} else if (ret < 0) {
 		/* failed to connect to the imap-master socket */
-		imap_client_destroy(&client, "Failed to connect to master socket");
+		imap_client_destroy(&client, error);
+		return TRUE;
+	}
+
+	int max_secs = client->input_pending ?
+		IMAP_CLIENT_MOVE_BACK_WITH_INPUT_TIMEOUT_SECS :
+		IMAP_CLIENT_MOVE_BACK_WITHOUT_INPUT_TIMEOUT_SECS;
+	if (ioloop_time - client->move_back_start > max_secs) {
+		/* we've waited long enough */
+		imap_client_destroy(&client, error);
+		return TRUE;
+	}
+	return FALSE;
+}
+
+static void imap_client_move_back(struct imap_client *client)
+{
+	if (imap_client_try_move_back(client))
+		return;
+
+	/* imap-master socket is busy. retry in a while. */
+	if (client->move_back_start == 0)
+		client->move_back_start = ioloop_time;
+	client->unhibernate_queued = TRUE;
+	priorityq_add(unhibernate_queue, &client->item);
+	if (to_unhibernate == NULL) {
+		to_unhibernate = timeout_add_short(IMAP_UNHIBERNATE_RETRY_MSECS,
+						   imap_clients_unhibernate, NULL);
 	}
 }
 
@@ -269,6 +321,7 @@
 		return;
 	}
 	client->idle_done = TRUE;
+	client->input_pending = TRUE;
 	imap_client_move_back(client);
 }
 
@@ -276,8 +329,10 @@
 {
 	if (i_stream_read(client->input) < 0)
 		imap_client_disconnected(&client);
-	else
+	else {
+		client->input_pending = TRUE;
 		imap_client_move_back(client);
+	}
 }
 
 static void imap_client_input_notify(struct imap_client *client)
@@ -459,6 +514,8 @@
 {
 	struct imap_client_notify *notify;
 
+	if (client->unhibernate_queued)
+		priorityq_remove(unhibernate_queue, &client->item);
 	if (client->io != NULL)
 		io_remove(&client->io);
 	if (client->to_keepalive != NULL)
@@ -541,6 +598,44 @@
 	}
 }
 
+static int client_unhibernate_cmp(const void *p1, const void *p2)
+{
+	const struct imap_client *c1 = p1, *c2 = p2;
+	time_t t1, t2;
+
+	t1 = c1->move_back_start +
+		(c1->input_pending ?
+		 IMAP_CLIENT_MOVE_BACK_WITH_INPUT_TIMEOUT_SECS :
+		 IMAP_CLIENT_MOVE_BACK_WITHOUT_INPUT_TIMEOUT_SECS);
+	t2 = c2->move_back_start +
+		(c1->input_pending ?
+		 IMAP_CLIENT_MOVE_BACK_WITH_INPUT_TIMEOUT_SECS :
+		 IMAP_CLIENT_MOVE_BACK_WITHOUT_INPUT_TIMEOUT_SECS);
+	if (t1 < t2)
+		return -1;
+	if (t1 > t2)
+		return 1;
+	return 0;
+}
+
+static void imap_clients_unhibernate(void *context ATTR_UNUSED)
+{
+	struct priorityq_item *item;
+
+	while ((item = priorityq_pop(unhibernate_queue)) != NULL) {
+		struct imap_client *client = (struct imap_client *)item;
+
+		if (!imap_client_try_move_back(client))
+			return;
+	}
+	timeout_remove(&to_unhibernate);
+}
+
+void imap_clients_init(void)
+{
+	unhibernate_queue = priorityq_init(client_unhibernate_cmp, 64);
+}
+
 void imap_clients_deinit(void)
 {
 	while (imap_clients != NULL) {
@@ -549,4 +644,7 @@
 		imap_client_io_activate_user(client);
 		imap_client_destroy(&client, "Shutting down");
 	}
+	if (to_unhibernate != NULL)
+		timeout_remove(&to_unhibernate);
+	priorityq_deinit(&unhibernate_queue);
 }

--- a/src/imap-hibernate/imap-client.h	Tue Aug 02 13:41:07 2016 +0300
+++ b/src/imap-hibernate/imap-client.h	Tue Jul 19 10:16:17 2016 -0600
@@ -31,6 +31,7 @@
 void imap_client_create_finish(struct imap_client *client);
 void imap_client_destroy(struct imap_client **_client, const char *reason);
 
+void imap_clients_init(void);
 void imap_clients_deinit(void);
 
 #endif

--- a/src/imap-hibernate/imap-master-connection.c	Tue Aug 02 13:41:07 2016 +0300
+++ b/src/imap-hibernate/imap-master-connection.c	Tue Jul 19 10:16:17 2016 -0600
@@ -28,7 +28,8 @@
 				imap_master_connection_send_callback_t *send_callback,
 				imap_master_connection_read_callback_t *read_callback,
 				void *context,
-				struct imap_master_connection **conn_r)
+				struct imap_master_connection **conn_r,
+				const char **error_r)
 {
 	struct imap_master_connection *conn;
 
@@ -38,15 +39,18 @@
 	conn->context = context;
 	connection_init_client_unix(master_clients, &conn->conn, path);
 	if (connection_client_connect(&conn->conn) < 0) {
-		i_error("net_connect_unix(%s) failed: %m", path);
+		int ret = errno == EAGAIN ? 0 : -1;
+
+		*error_r = t_strdup_printf(
+			"net_connect_unix(%s) failed: %m", path);
 		connection_deinit(&conn->conn);
 		i_free(conn);
-		return -1;
+		return ret;
 	}
 	conn->to = timeout_add(IMAP_MASTER_CONNECTION_TIMEOUT_MSECS,
 			       imap_master_connection_timeout, conn);
 	*conn_r = conn;
-	return 0;
+	return 1;
 }
 
 void imap_master_connection_deinit(struct imap_master_connection **_conn)

--- a/src/imap-hibernate/imap-master-connection.h	Tue Aug 02 13:41:07 2016 +0300
+++ b/src/imap-hibernate/imap-master-connection.h	Tue Jul 19 10:16:17 2016 -0600
@@ -8,11 +8,13 @@
 typedef void
 imap_master_connection_read_callback_t(void *context, const char *reply);
 
+/* Returns 1 = success, 0 = retry later, -1 = error */
 int imap_master_connection_init(const char *path,
 				imap_master_connection_send_callback_t *send_callback,
 				imap_master_connection_read_callback_t *read_callback,
 				void *context,
-				struct imap_master_connection **conn_r);
+				struct imap_master_connection **conn_r,
+				const char **error_r);
 void imap_master_connection_deinit(struct imap_master_connection **conn);
 
 void imap_master_connections_init(void);

--- a/src/imap-hibernate/main.c	Tue Aug 02 13:41:07 2016 +0300
+++ b/src/imap-hibernate/main.c	Tue Jul 19 10:16:17 2016 -0600
@@ -42,6 +42,7 @@
 	restrict_access_by_env(NULL, FALSE);
 	restrict_access_allow_coredumps(TRUE);
 
+	imap_clients_init();
 	imap_master_connections_init();
 	imap_hibernate_clients_init();
 	master_service_init_finish(master_service);