Idle connection culling support (#252)

* Idle connection culling support

Author: bretambrose

include/aws/http/connection_manager.h

@@ -69,6 +69,12 @@ struct aws_http_connection_manager_options {
      * If set to true, the read back pressure mechanism will be enabled.
      */
     bool enable_read_back_pressure;
+
+    /**
+     * If set to a non-zero value, then connections that stay in the pool longer than the specified
+     * timeout will be closed automatically.
+     */
+    uint64_t max_connection_idle_in_milliseconds;
 };
 
 AWS_EXTERN_C_BEGIN

include/aws/http/private/connection_manager_system_vtable.h

@@ -24,6 +24,9 @@ typedef int(aws_http_connection_manager_create_connection_fn)(const struct aws_h
 typedef void(aws_http_connection_manager_close_connection_fn)(struct aws_http_connection *connection);
 typedef void(aws_http_connection_manager_release_connection_fn)(struct aws_http_connection *connection);
 typedef bool(aws_http_connection_manager_is_connection_open_fn)(const struct aws_http_connection *connection);
+typedef bool(aws_http_connection_manager_is_callers_thread_fn)(struct aws_channel *channel);
+typedef struct aws_channel *(aws_http_connection_manager_connection_get_channel_fn)(
+    struct aws_http_connection *connection);
 
 struct aws_http_connection_manager_system_vtable {
     /*
@@ -33,6 +36,9 @@ struct aws_http_connection_manager_system_vtable {
     aws_http_connection_manager_close_connection_fn *close_connection;
     aws_http_connection_manager_release_connection_fn *release_connection;
     aws_http_connection_manager_is_connection_open_fn *is_connection_open;
+    aws_io_clock_fn *get_monotonic_time;
+    aws_http_connection_manager_is_callers_thread_fn *is_callers_thread;
+    aws_http_connection_manager_connection_get_channel_fn *connection_get_channel;
 };
 
 AWS_HTTP_API