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Reverting changeset 1.1590

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guilhem@mysql.com 2003-10-02 16:25:47 +02:00
parent 8c13c30142
commit 9f4d29c3f3
1 changed files with 2 additions and 23 deletions
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25
sql/slave.h
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@ -171,31 +171,10 @@ typedef struct st_relay_log_info
Handling of the relay_log_space_limit optional constraint.
ignore_log_space_limit is used to resolve a deadlock between I/O and SQL
threads, the SQL thread sets it to unblock the I/O thread and make it
temporarily forget about the constraint. It is declared volatile because we
have this loop in the I/O thread (slave.cc):
while (rli->log_space_limit < rli->log_space_total &&
!(slave_killed=io_slave_killed(thd,mi)) &&
!rli->ignore_log_space_limit)
pthread_cond_wait(&rli->log_space_cond, &rli->log_space_lock);
According to Monty, on some systems pthread_cond_wait() could be inline,
and so the loop be optimized by the compiler, so rli->ignore_log_space_limit
could be considered constant and the loop never ends, even if the SQL thread
has set rli->ignore_log_space_limit to 1 (and called
pthread_cond_broadcast()) to break the loop in the I/O thread.
By declaring it volatile, we are sure that the variable will not be
considered constant and that the loop can be broken.
This is the same for all bool variables used by a thread to inform another
thread that something has changed: thd->killed, rli->abort_slave,
MYSQL_LOG::log_type; they are all volatile.
Quoting:
<serg> while (a>0) { wait_for_condition }
<serg> here a should be volatile ?
<monty> serg: in most system no, but on some yes
<serg> on what systems ?
<monty> On any system where pthread_mutex is a macro.
temporarily forget about the constraint.
*/
ulonglong log_space_limit,log_space_total;
volatile bool ignore_log_space_limit;
bool ignore_log_space_limit;
/*
InnoDB internally stores the master log position it has processed