After the merge of VIO stuff from MySQL 5.6, there were some bugs left
in the non-blocking client library:
- vio_io_wait() was introduced without any support for non-blocking operation,
so async queries could turn into sync.
- Timeouts were changed to milliseconds, but this was not reflected in the
non-blocking API, also semantics was changed so signed -1 was used for
"no timeout" rather than unsigned 0.
Fix by implementing and using my_io_wait_async() in the non-blocking case. And
by introducing a new mysql_get_timeout_value_ms() API function that provides
the timeout with millisecond granularity. The old mysql_get_timeout_value()
is kept and fixed to work correctly, converting the timeout to whole seconds.
Main change is that non-blocking operation is now an option that must be
explicitly enabled with mysql_option(mysql, MYSQL_OPT_NONBLOCK, ...)
before any non-blocing operation can be used.
Also the CLIENT_REMEMBER_OPTIONS flag is now always enabled and thus
effectively ignored (it was not really useful anyway, and this simplifies
things when non-blocking mysql_real_connect() fails).
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.
