Bug#56618 Thread_ID is not assigned in ascending sequence (after disconnect)

Before this fix, the test thread_cache failed with spurious failures.

The test used:
-- disconnect X
-- connect Y

while assuming that connection Y would reuse connection X slot in the thread cache.

For this to happen, the disconnect X operation must be given enough time to complete,
otherwise connect Y can be executed in the server before X actually finishes.

This fix uses wait conditions to make the test execution more controlled,
and more reproductible.

mysql-test/suite/perfschema/r/thread_cache.result

+flush status;
 SET @saved_thread_cache_size = @@global.thread_cache_size;
 set global thread_cache_size = 0;
 show variables like "thread_cache_size";
@@ -32,3 +33,7 @@ select @thread_id_increment;
 @thread_id_increment
 1
 set global thread_cache_size = @saved_thread_cache_size;
+show status like "performance_schema_thread%";
+Variable_name	Value
+Performance_schema_thread_classes_lost	0
+Performance_schema_thread_instances_lost	0

mysql-test/suite/perfschema/t/thread_cache.test

@@ -20,6 +20,8 @@
 
 # Setup
 
+flush status;
+
 SET @saved_thread_cache_size = @@global.thread_cache_size;
 
 set global thread_cache_size = 0;
@@ -40,7 +42,7 @@ let $con2_ID=`select connection_id()`;
 let $con2_THREAD_ID=`select thread_id from performance_schema.threads
   where PROCESSLIST_ID = connection_id()`;
 
-connection default;
+--connection default
 
 --disable_query_log
 eval select ($con2_ID - $con1_ID) into @id_increment;
@@ -52,7 +54,15 @@ select @id_increment;
 # Expect 1, THREAD_ID is incremented for each new connection
 select @thread_id_increment;
 
-disconnect con2;
+--disconnect con2
+
+--connection default
+
+# Wait for the disconnect con2 to complete
+let $wait_condition=
+  select count(*) = 2 from performance_schema.threads
+  where name like "thread/sql/one_connection";
+--source include/wait_condition.inc
 
 connect (con3, localhost, root, , );
 
@@ -61,10 +71,16 @@ let $con3_ID=`select connection_id()`;
 let $con3_THREAD_ID=`select thread_id from performance_schema.threads
   where PROCESSLIST_ID = connection_id()`;
 
-disconnect con3;
-disconnect con1;
+--disconnect con3
+--disconnect con1
+
+--connection default
 
-connection default;
+# Wait for the disconnect con1 and con3 to complete
+let $wait_condition=
+  select count(*) = 1 from performance_schema.threads
+  where name like "thread/sql/one_connection";
+--source include/wait_condition.inc
 
 --disable_query_log
 eval select ($con3_ID - $con2_ID) into @id_increment;
@@ -92,7 +108,7 @@ let $con2_ID=`select connection_id()`;
 let $con2_THREAD_ID=`select thread_id from performance_schema.threads
   where PROCESSLIST_ID = connection_id()`;
 
-connection default;
+--connection default
 
 --disable_query_log
 eval select ($con2_ID - $con1_ID) into @id_increment;
@@ -102,7 +118,15 @@ eval select ($con2_THREAD_ID - $con1_THREAD_ID) into @thread_id_increment;
 select @id_increment;
 select @thread_id_increment;
 
-disconnect con2;
+--disconnect con2
+
+--connection default
+
+# Wait for the disconnect con2 to complete
+let $wait_condition=
+  select count(*) = 2 from performance_schema.threads
+  where name like "thread/sql/one_connection";
+--source include/wait_condition.inc
 
 connect (con3, localhost, root, , );
 
@@ -111,10 +135,16 @@ let $con3_ID=`select connection_id()`;
 let $con3_THREAD_ID=`select thread_id from performance_schema.threads
   where PROCESSLIST_ID = connection_id()`;
 
-disconnect con3;
-disconnect con1;
+--disconnect con3
+--disconnect con1
 
-connection default;
+--connection default
+
+# Wait for the disconnect con1 and con3 to complete
+let $wait_condition=
+  select count(*) = 1 from performance_schema.threads
+  where name like "thread/sql/one_connection";
+--source include/wait_condition.inc
 
 --disable_query_log
 eval select ($con3_ID - $con2_ID) into @id_increment;
@@ -132,3 +162,5 @@ select @thread_id_increment;
 
 set global thread_cache_size = @saved_thread_cache_size;
 
+show status like "performance_schema_thread%";
+