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MWL#192: Non-blocking client API for libmysqlclient.
All client functions that can block on I/O have alternate _start() and _cont() versions that do not block but return control back to the application, which can then issue I/O wait in its own fashion and later call back into the library to continue the operation. Works behind the scenes by spawning a co-routine/fiber to run the blocking operation and suspend it while waiting for I/O. This co-routine/fiber use is invisible to applications. For i368/x86_64 on GCC, uses very fast assembler co-routine support. On Windows uses native Win32 Fibers. Falls back to POSIX ucontext on other platforms. Assembler routines for more platforms are relatively easy to add by extending mysys/my_context.c, eg. similar to the Lua lcoco library. For testing, mysqltest and mysql_client_test are extended with the option --non-blocking-api. This causes the programs to use the non-blocking API for database access. mysql-test-run.pl has a similar option --non-blocking-api that uses this, as well as additional testcases. An example program tests/async_queries.c is included that uses the new non-blocking API with libevent to show how, in a single-threaded program, to issue many queries in parallel against a database. client/async_example.c: Fix const warning ****** Fix bug with wrong timeout value for poll(). include/Makefile.am: Fix missing include for `make dist` include/mysql.h: Add prototypes for all non-blocking API calls. include/mysql.h.pp: Add prototypes for all non-blocking API calls. mysys/my_context.c: Fix type warning for makecontext() function pointer argument. sql-common/mysql_async.c: Fix crashes in the non-blocking API for functions that can take MYSQL argument that is NULL. tests/Makefile.am: Add header file to `make dist` tests/mysql_client_test.c: Replace blocking calls with wrappers around the non-blocking calls, used in mysql_client_test to test the new non-blocking API. tests/nonblock-wrappers.h: Replace blocking calls with wrappers around the non-blocking calls, used in mysql_client_test to test the new non-blocking API.
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client/async_example.c
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207
client/async_example.c
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/*
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Copyright 2011 Kristian Nielsen and Monty Program Ab.
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Experiments with non-blocking libmysql.
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This is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 2 of the License, or
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(at your option) any later version.
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This is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this. If not, see <http://www.gnu.org/licenses/>.
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*/
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#ifndef __WIN__
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#include <poll.h>
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#else
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#include <WinSock2.h>
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#endif
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#include <stdlib.h>
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#include <stdio.h>
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#include <mysql.h>
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#define SL(s) (s), sizeof(s)
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static const char *my_groups[]= { "client", NULL };
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static int
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wait_for_mysql(MYSQL *mysql, int status)
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{
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#ifdef __WIN__
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fd_set rs, ws, es;
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int res;
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struct timeval tv, *timeout;
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my_socket s= mysql_get_socket(mysql);
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FD_ZERO(&rs);
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FD_ZERO(&ws);
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FD_ZERO(&es);
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if (status & MYSQL_WAIT_READ)
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FD_SET(s, &rs);
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if (status & MYSQL_WAIT_WRITE)
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FD_SET(s, &ws);
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if (status & MYSQL_WAIT_EXCEPT)
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FD_SET(s, &es);
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if (status & MYSQL_WAIT_TIMEOUT)
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{
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tv.tv_sec= mysql_get_timeout_value(mysql);
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tv.tv_usec= 0;
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timeout= &tv;
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}
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else
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timeout= NULL;
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res= select(1, &rs, &ws, &es, timeout);
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if (res == 0)
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return MYSQL_WAIT_TIMEOUT;
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else if (res == SOCKET_ERROR)
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{
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/*
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In a real event framework, we should handle errors and re-try the select.
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*/
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return MYSQL_WAIT_TIMEOUT;
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}
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else
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{
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int status= 0;
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if (FD_ISSET(s, &rs))
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status|= MYSQL_WAIT_READ;
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if (FD_ISSET(s, &ws))
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status|= MYSQL_WAIT_WRITE;
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if (FD_ISSET(s, &es))
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status|= MYSQL_WAIT_EXCEPT;
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return status;
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}
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#else
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struct pollfd pfd;
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int timeout;
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int res;
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pfd.fd= mysql_get_socket(mysql);
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pfd.events=
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(status & MYSQL_WAIT_READ ? POLLIN : 0) |
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(status & MYSQL_WAIT_WRITE ? POLLOUT : 0) |
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(status & MYSQL_WAIT_EXCEPT ? POLLPRI : 0);
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if (status & MYSQL_WAIT_TIMEOUT)
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timeout= 1000*mysql_get_timeout_value(mysql);
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else
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timeout= -1;
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res= poll(&pfd, 1, timeout);
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if (res == 0)
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return MYSQL_WAIT_TIMEOUT;
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else if (res < 0)
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{
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/*
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In a real event framework, we should handle EINTR and re-try the poll.
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*/
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return MYSQL_WAIT_TIMEOUT;
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}
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else
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{
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int status= 0;
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if (pfd.revents & POLLIN)
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status|= MYSQL_WAIT_READ;
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if (pfd.revents & POLLOUT)
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status|= MYSQL_WAIT_WRITE;
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if (pfd.revents & POLLPRI)
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status|= MYSQL_WAIT_EXCEPT;
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return status;
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}
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#endif
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}
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static void
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fatal(MYSQL *mysql, const char *msg)
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{
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fprintf(stderr, "%s: %s\n", msg, mysql_error(mysql));
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exit(1);
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}
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static void
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doit(const char *host, const char *user, const char *password)
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{
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int err;
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MYSQL mysql, *ret;
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MYSQL_RES *res;
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MYSQL_ROW row;
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int status;
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mysql_init(&mysql);
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mysql_options(&mysql, MYSQL_READ_DEFAULT_GROUP, "myapp");
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/* Returns 0 when done, else flag for what to wait for when need to block. */
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status= mysql_real_connect_start(&ret, &mysql, host, user, password, NULL,
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0, NULL, 0);
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while (status)
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{
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status= wait_for_mysql(&mysql, status);
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status= mysql_real_connect_cont(&ret, &mysql, status);
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}
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if (!ret)
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fatal(&mysql, "Failed to mysql_real_connect()");
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status= mysql_real_query_start(&err, &mysql, SL("SHOW STATUS"));
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while (status)
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{
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status= wait_for_mysql(&mysql, status);
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status= mysql_real_query_cont(&err, &mysql, status);
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}
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if (err)
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fatal(&mysql, "mysql_real_query() returns error");
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/* This method cannot block. */
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res= mysql_use_result(&mysql);
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if (!res)
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fatal(&mysql, "mysql_use_result() returns error");
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for (;;)
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{
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status= mysql_fetch_row_start(&row, res);
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while (status)
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{
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status= wait_for_mysql(&mysql, status);
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status= mysql_fetch_row_cont(&row, res, status);
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}
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if (!row)
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break;
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printf("%s: %s\n", row[0], row[1]);
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}
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if (mysql_errno(&mysql))
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fatal(&mysql, "Got error while retrieving rows");
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mysql_free_result(res);
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/* I suppose this must be non-blocking too. */
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mysql_close(&mysql);
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}
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int
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main(int argc, char *argv[])
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{
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int err;
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if (argc != 4)
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{
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fprintf(stderr, "Usage: %s <host> <user> <password>\n", argv[0]);
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exit(1);
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}
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err= mysql_library_init(argc, argv, (char **)my_groups);
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if (err)
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{
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fprintf(stderr, "Fatal: mysql_library_init() returns error: %d\n", err);
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exit(1);
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}
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doit(argv[1], argv[2], argv[3]);
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mysql_library_end();
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return 0;
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}
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