class PG::CancelConnection
The class to represent a connection to cancel a query.
On PostgreSQL-17+ client libaray this class is used to implement PG::Connection#cancel . It works on older PostgreSQL server versions too.
Available since PostgreSQL-17
Attributes
These private methods are there to allow a shared polling_loop.
Public Class Methods
Source
VALUE
pg_cancon_initialize(VALUE self, VALUE rb_conn)
{
t_pg_cancon *this = pg_cancon_get_this(self);
PGconn *conn = pg_get_pgconn(rb_conn);
this->pg_cancon = PQcancelCreate(conn);
if (this->pg_cancon == NULL)
pg_raise_conn_error( rb_eConnectionBad, self, "PQcancelCreate failed");
return self;
}
Prepares a connection over which a cancel request can be sent.
Creates a PG::CancelConnection from a PG::Connection object, but it won’t instantly start sending a cancel request over this connection. A cancel request can be sent over this connection in a blocking manner using cancel and in a non-blocking manner using start. status can be used to check if the PG::CancelConnection object was connected successfully. This PG::CancelConnection object can be used to cancel the query that’s running on the original connection in a thread-safe way.
Many connection parameters of the original client will be reused when setting up the connection for the cancel request. Importantly, if the original connection requires encryption of the connection and/or verification of the target host (using sslmode or gssencmode), then the connection for the cancel request is made with these same requirements. Any connection options that are only used during authentication or after authentication of the client are ignored though, because cancellation requests do not require authentication and the connection is closed right after the cancellation request is submitted.
Source
# File lib/pg/cancel_connection.rb, line 11 def initialize(conn) c_initialize(conn) # A cancel connection is always to one destination server only. # Prepare conninfo_hash with just enough information to allow a shared polling_loop. @host = conn.host @hostaddr = conn.hostaddr @port = conn.port @conninfo_hash = { host: @host, hostaddr: @hostaddr, port: @port.to_s, connect_timeout: conn.conninfo_hash[:connect_timeout], } end
Public Instance Methods
Source
# File lib/pg/cancel_connection.rb, line 39 def cancel start polling_loop(:poll) end
Requests that the server abandons processing of the current command in a blocking manner.
If the cancel request wasn’t successfully dispatched an error message is raised.
Successful dispatch of the cancellation is no guarantee that the request will have any effect, however. If the cancellation is effective, the command being canceled will terminate early and raises an error. If the cancellation fails (say, because the server was already done processing the command), then there will be no visible result at all.
Source
static VALUE
pg_cancon_error_message(VALUE self)
{
PGcancelConn *conn = pg_cancon_get_conn(self);
char *p_err;
p_err = PQcancelErrorMessage(conn);
return p_err ? rb_str_new_cstr(p_err) : Qnil;
}
Returns the error message most recently generated by an operation on the cancel connection.
Nearly all PG::CancelConnection functions will set a message if they fail. Note that by libpq convention, a nonempty error_message result can consist of multiple lines, and will include a trailing newline.
Source
static VALUE
pg_cancon_finish(VALUE self)
{
t_pg_cancon *this = pg_cancon_get_this( self );
pg_cancon_close_socket_io( self );
if( this->pg_cancon )
PQcancelFinish(this->pg_cancon);
this->pg_cancon = NULL;
return Qnil;
}
Closes the cancel connection (if it did not finish sending the cancel request yet). Also frees memory used by the PG::CancelConnection object.
Source
static VALUE
pg_cancon_poll(VALUE self)
{
PostgresPollingStatusType status;
PGcancelConn *conn = pg_cancon_get_conn(self);
pg_cancon_close_socket_io( self );
status = gvl_PQcancelPoll(conn);
return INT2FIX((int)status);
}
This is to poll libpq so that it can proceed with the cancel connection sequence.
The behavior is the same like PG::Connection#connect_poll .
See also corresponding libpq function
Source
static VALUE
pg_cancon_reset(VALUE self)
{
PGcancelConn *conn = pg_cancon_get_conn(self);
pg_cancon_close_socket_io( self );
PQcancelReset(conn);
return Qnil;
}
Resets the PG::CancelConnection so it can be reused for a new cancel connection.
If the PG::CancelConnection is currently used to send a cancel request, then this connection is closed. It will then prepare the PG::CancelConnection object such that it can be used to send a new cancel request.
This can be used to create one PG::CancelConnection for a PG::Connection and reuse it multiple times throughout the lifetime of the original PG::Connection.
Source
static VALUE
pg_cancon_socket_io(VALUE self)
{
t_pg_cancon *this = pg_cancon_get_this( self );
if ( !RTEST(this->socket_io) ) {
int sd;
if( (sd = PQcancelSocket(this->pg_cancon)) < 0){
pg_raise_conn_error( rb_eConnectionBad, self, "PQcancelSocket() can't get socket descriptor");
}
return pg_wrap_socket_io( sd, self, &this->socket_io, &this->ruby_sd);
}
return this->socket_io;
}
Fetch an IO object created from the CancelConnection’s underlying socket. This object can be used per socket_io.wait_readable, socket_io.wait_writable or for IO.select to wait for events while running asynchronous API calls. IO#wait_*able is Fiber.scheduler compatible in contrast to IO.select.
The IO object can change while the connection is established. So be sure not to cache the IO object, but repeat calling conn.socket_io instead.
Source
static VALUE
pg_cancon_start(VALUE self)
{
PGcancelConn *conn = pg_cancon_get_conn(self);
pg_cancon_close_socket_io( self );
if(gvl_PQcancelStart(conn) == 0)
pg_raise_conn_error( rb_eConnectionBad, self, "PQcancelStart %s", PQcancelErrorMessage(conn));
return Qnil;
}
Requests that the server abandons processing of the current command in a non-blocking manner.
The behavior is the same like PG::Connection.connect_start .
Use poll to poll the status of the connection.
Source
static VALUE
pg_cancon_status(VALUE self)
{
ConnStatusType status;
PGcancelConn *conn = pg_cancon_get_conn(self);
status = PQcancelStatus(conn);
return INT2NUM(status);
}
Returns the status of the cancel connection.
The status can be one of a number of values. However, only three of these are seen outside of an asynchronous cancel procedure: CONNECTION_ALLOCATED, CONNECTION_OK and CONNECTION_BAD. The initial state of a PG::CancelConnection that’s successfully created is CONNECTION_ALLOCATED. A cancel request that was successfully dispatched has the status CONNECTION_OK. A failed cancel attempt is signaled by status CONNECTION_BAD. An OK status will remain so until finish or reset is called.
See poll with regards to other status codes that might be returned.
Successful dispatch of the cancellation is no guarantee that the request will have any effect, however. If the cancellation is effective, the command being canceled will terminate early and return an error result. If the cancellation fails (say, because the server was already done processing the command), then there will be no visible result at all.
Source
static VALUE
pg_cancon_sync_cancel(VALUE self)
{
PGcancelConn *conn = pg_cancon_get_conn(self);
pg_cancon_close_socket_io( self );
if(gvl_PQcancelBlocking(conn) == 0)
pg_raise_conn_error( rb_eConnectionBad, self, "PQcancelBlocking %s", PQcancelErrorMessage(conn));
return Qnil;
}
Requests that the server abandons processing of the current command in a blocking manner.
This method directly calls PQcancelBlocking of libpq, so that it doesn’t respond to ruby interrupts and doesn’t trigger the Thread.scheduler . It is threrfore recommended to call cancel instead.