Concurrent execution of statements which require non-table-level
write locks on several instances of the same table (such as
SELECT ... FOR UPDATE which uses same InnoDB table twice or a DML
statement which invokes trigger which tries to update same InnoDB
table directly and through stored function) and statements which
required table-level locks on this table (e.g. LOCK TABLE ... WRITE,
ALTER TABLE, ...) might have resulted in a deadlock.
The problem occured when a thread tried to acquire write lock
(TL_WRITE_ALLOW_WRITE) on the table but had to wait since there was
a pending write lock (TL_WRITE, TL_WRITE_ALLOW_READ) on this table
and we failed to detect that this thread already had another instance
of write lock on it (so in fact we were trying to acquire recursive
lock) because there was also another thread holding write lock on the
table (also TL_WRITE_ALLOW_WRITE). When the latter thread released
its lock neither the first thread nor the thread trying to acquire
TL_WRITE/TL_WRITE_ALLOW_READ were woken up (as table was still write
locked by the first thread) so we ended up with a deadlock.
This patch solves this problem by ensuring that thread which
already has write lock on the table won't wait when it tries
to acquire second write lock on the same table.
The pthread_cond_wait implementations for windows might
dead lock in some rare circumstances.
1) One thread (I) enter a timed wait and at a point in
time ends up after mutex unlock and before
WaitForMultipleObjects(...)
2) Another thread (II) enters pthread_cond_broadcast.
Grabs the mutex and discovers one waiter. It set
the broadcast event and closes the broadcast gate
then unlocks the mutex.
3) A third thread (III) issues a pthread_cond_signal.
It grabs the mutex, discovers one waiter, sets the
signal event then unlock the mutex.
4) The first threads (I) enters WaitForMultipleObjects
and finds out that the signal object is in a
signalled state and exits the wait.
5) Thread (I) grabs the mutex and checks result status.
The number of waiters is decreased and becomes equal
to 0. The event returned was a signal event so the
broadcast gate isn't opened. The mutex is released.
6) Thread (II) issues a new broadcast. The mutex is
acquired but the number of waiters are 0 hence
the broadcast gate remains closed.
7) Thread (I) enters the wait again but is blocked by
the broadcast gate.
This fix resolves the above issue by always resetting
broadcast gate when there are no more waiters in th queue.
http://lists.mysql.com/commits/59686
Cleanup pthread_self(), pthread_create(), pthread_join() implementation on Windows.
Prior implementation is was unnecessarily complicated and even differs in embedded
and non-embedded case.
Improvements in this patch:
* pthread_t is now the unique thread ID, instead of HANDLE returned by beginthread
This simplifies pthread_self() to be just straight GetCurrentThreadId().
prior it was much art involved in passing the beginthread() handle from the caller
to the TLS structure in the child thread ( did not work for the main thread of
course)
* remove MySQL specific my_thread_init()/my_thread_end() from pthread_create.
No automagic is done on Unix on pthread_create(). Having the same on Windows will
improve portability and avoid extra #ifdef's
* remove redefinition of getpid() - it was defined as GetCurrentThreadId()
2677 Vladislav Vaintroub 2008-11-04
CMakeLists.txt files cleanup
- remove SAFEMALLOC and SAFE_MUTEX definitions that were
present in *each* CMakeLists.txt. Instead, put them into top level
CMakeLists.txt, but disable on Windows, because
a) SAFEMALLOC does not add any functionality that is not already
present in Debug C runtime ( and 2 safe malloc one on top of the other
only unnecessarily slows down the server)
b)SAFE_MUTEX does not work on Windows and have been
explicitely disabled on Windows with #undef previously. Fortunately,
ntdll does pretty good job identifying l problems with
CRITICAL_SECTIONs.
DebugBreak()s on using uninited critical section, unlocking unowned
critical section)
-Also, remove occationally used -D_DEBUG (added by compiler
anyway)
This patch provides performance improvements:
- send_fields() when character_set_results = latin1
is now about twice faster for column/table/database
names, consisting on ASCII characters.
Changes:
- Protocol doesn't use "convert" temporary buffer anymore,
and converts strings directly to "packet".
- General conversion optimization: quick conversion
of ASCII strings was added.
modified files:
include/m_ctype.h
- Adding a new flag.
- Adding a new function prototype
libmysqld/lib_sql.cc
- Adding quick conversion method for embedded library:
conversion is now done directly to result buffer,
without using a temporary buffer.
mysys/charset.c
- Mark all dynamic ucs2 character sets as non-ASCII
- Mark some dymamic 7bit and 8bit charsets as non-ASCII
(for example swe7 is not fully ASCII compatible).
sql/protocol.cc
- Adding quick method to convert a string directly
into protocol buffer, without using a temporary buffer.
sql/protocol.h
- Adding a new method prototype
sql/sql_string.cc
Optimization for conversion between two ASCII-compatible charsets:
- quickly convert ASCII strings,
switch to mc_wc->wc_mb method only when a non-ASCII character is met.
- copy four ASCII characters at once on i386
strings/conf_to_src.c
- Marking non-ASCII character sets with a flag.
strings/ctype-extra.c
- Regenerating ctype-extra.c by running "conf_to_src".
strings/ctype-uca.c
- Marking UCS2 character set as non-ASCII.
strings/ctype-ucs2.c
- Marking UCS2 character set as non-ASCII.
strings/ctype.c
- A new function to detect if a 7bit or 8bit character set
is ascii compatible.
http://lists.mysql.com/commits/57725
Vladislav Vaintroub 2008-11-03
Cleanup CMakeLists.txt(s) - remove winsock2 (ws2_32) from
TARGET_LINK_LIBRARIES.
Every exe or dll linked with mysys needs ws2_32, because
mysys uses winsock function WSAStartup in my_init().
However, there is no need to explicitely add ws2_32 to
the list of TARGET_LINK_LIBRARIES multiple times.
Visual Studio comes with a handy pragma that tells linker
to add library. So patch replaces bunch of ws2_32 in
CMakeLists with single pragma comment(lib,"ws2_32")
in my_init.c
Additionally, reference to non-existing "debug" library
has been removed from TARGET_LINK_LIBRARIES. The correct
name of the library is "dbug".
htttp://lists.mysql.com/commits/50957?f=plain
Always use TLS functions instead of __declspec(thread) to access
thread local storage variables.
The change removes the necessity to recomplile the same source
files twice - with USE_TLS for DLLs and without USE_TLS for EXEs.
Real benefit of this change is better readability and maintainability
of TLS functions within MySQL.
There is a performance loss using TlsXXX functions compared to __declspec
but the difference is negligible in practice. In a sysbench-like benchmark
I ran with with TlsGetValue, pthread_[get|set]_specific was called 600000000
times and took 0.17sec of total 35min CPU time, or 0.008%.
Backport from 6.0 to 5.1.
Only those sync points are included, which are used in debug_sync.test.
The Debug Sync Facility allows to place synchronization points
in the code:
open_tables(...)
DEBUG_SYNC(thd, "after_open_tables");
lock_tables(...)
When activated, a sync point can
- Send a signal and/or
- Wait for a signal
Nomenclature:
- signal: A value of a global variable that persists
until overwritten by a new signal. The global
variable can also be seen as a "signal post"
or "flag mast". Then the signal is what is
attached to the "signal post" or "flag mast".
- send a signal: Assign the value (the signal) to the global
variable ("set a flag") and broadcast a
global condition to wake those waiting for
a signal.
- wait for a signal: Loop over waiting for the global condition until
the global value matches the wait-for signal.
Please find more information in the top comment in debug_sync.cc
or in the worklog entry.
- Create the "dummy" thread joinable and wait for it to
exit before continuing in 'my_thread_global_init'
- This way we know that the pthread library is initialized
by one thread only
Option "--without-server" still not working in 5.1
The general approach is to make sure that source files
which require thread support are only compiled if the build
really needs thread support,
which means when the server is built or a thread-safe client
library.
This required several changes:
- Make sure the subdirectories "storage/" and "plugin/" are
only processed if the server is built, not ifclient-only.
- Make the compilation of some modules which inherently
require threading depend on thread supportin the build.
- Separate the handling of threading in "configure.in" from
that of server issues, threading is also needed in a
non-server build of a thread-safe client library.
Also, "libdbug" must get built even in a client-only build,
so "dbug/" must be in the list of client directories.
In addition, calls to thread functions in source files which
can be built without thread support must use the wrapper
functions which handle the non-threaded build.
So the modules "client/mysqlimport.c" and "client/mysqlslap.c"
must call "my_thread_end()" only via "mysql_thread_end()".
