In {{{tokudb.3039}}} and {{{tokudb}}} merge fix for #3142. Fixes #3142. close[t:3142]

{{{
svn merge -r26654:26656 https://svn.tokutek.com/tokudb/toku/tokudb.3039c+3131
}}}


git-svn-id: file:///svn/toku/tokudb@26659 c7de825b-a66e-492c-adef-691d508d4ae1

src/ydb.c

@@ -71,7 +71,7 @@ static u_int64_t directory_write_locks_fail;  /* total directory write locks una
 static u_int64_t logsuppress;                // number of times logs are suppressed for empty table (2440)
 static u_int64_t logsuppressfail;            // number of times unable to suppress logs for empty table (2440)
 static time_t    startuptime;                // timestamp of system startup
-static DB_ENV *  most_recent_env;            // most recently opened env, used for engine status on crash
+volatile static DB_ENV *  most_recent_env;   // most recently opened env, used for engine status on crash.  Note there are likely to be races on this if you have multiple threads creating and closing environments in parallel.  We'll declare it volatile since at least that helps make sure the compiler doesn't optimize away certain code (e.g., if while debugging, you write a code that spins on most_recent_env, you'd like to compiler not to optimize your code away.)
 
 static uint32_t  engine_status_enable = 1;   // if zero, suppress engine status output on failed assert, for test programs only
 
@@ -982,7 +982,7 @@ toku_env_open(DB_ENV * env, const char *home, u_int32_t flags, int mode) {
         }
     }
     if (r == 0) {
-	errno = 0; // tabula rasa
+	errno = 0; // tabula rasa.   If there's a crash after env was successfully opened, no misleading errno will have been left around by this code.
 	most_recent_env = env;
     }
     return r;
@@ -992,6 +992,8 @@ static int
 toku_env_close(DB_ENV * env, u_int32_t flags) {
     int r = 0;
 
+    most_recent_env = NULL; // Set most_recent_env to NULL so that we don't have a dangling pointer (and if there's an error, the toku assert code would try to look at the env.)
+
     // if panicked, or if any open transactions, or any open dbs, then do nothing.
 
     if (toku_env_is_panicked(env)) goto panic_and_quit_early;