MDEV-31809 Make SST script interface read-write

Add two-way communication between parent and child in wsp::proc class. Refactor wsp::thd class to call my_thread_init() conditionally. Signed-off-by: Julius Goryavsky <julius.goryavsky@mariadb.com>

Author: ayurchen

sql/wsrep_sst.cc

@@ -107,8 +107,7 @@ static void* wsrep_sst_donor_monitor_thread(void *arg __attribute__((unused)))
 
  WSREP_INFO("Donor monitor thread started to monitor");
 
- wsp::thd thd(FALSE); // we turn off wsrep_on for this THD so that it can
- // operate with wsrep_ready == OFF
+ wsp::thd thd;
 
  while (!sst_donor_completed)
  {
@@ -144,8 +143,7 @@ static void* wsrep_sst_joiner_monitor_thread(void *arg __attribute__((unused)))
 
  WSREP_INFO("Joiner monitor thread started to monitor");
 
- wsp::thd thd(FALSE); // we turn off wsrep_on for this THD so that it can
- // operate with wsrep_ready == OFF
+ wsp::thd thd;
 
  while (!sst_joiner_completed)
  {
@@ -642,9 +640,9 @@ static void* sst_joiner_thread (void* a)
 
  wsp::process proc (arg->cmd, "r", arg->env);
 
- if (proc.pipe() && !proc.error())
+ if (proc.from() && !proc.error())
  {
- const char* tmp= my_fgets (out, out_len, proc.pipe());
+ const char* tmp= my_fgets (out, out_len, proc.from());
 
  if (!tmp || strlen(tmp) < (magic_len + 2) ||
  strncasecmp (tmp, magic, magic_len))
@@ -698,7 +696,7 @@ static void* sst_joiner_thread (void* a)
  err= EINVAL;
 
  wait_signal:
- tmp= my_fgets (out, out_len, proc.pipe());
+ tmp= my_fgets (out, out_len, proc.from());
 
  if (tmp)
  {
@@ -1534,7 +1532,7 @@ static int sst_run_shell (const char* cmd_str, char** env, int max_tries)
  {
  wsp::process proc (cmd_str, "r", env);
 
- if (NULL != proc.pipe())
+ if (NULL != proc.from())
  {
  proc.wait();
  }
@@ -1847,26 +1845,32 @@ static void* sst_donor_thread (void* a)
  // We turn off wsrep_on for this THD so that it can
  // operate with wsrep_ready == OFF
  // We also set this SST thread THD as system thread
- wsp::thd thd(FALSE, true);
+ wsp::thd thd(true, true);
  wsp::process proc(arg->cmd, "r", arg->env);
 
  err= -proc.error();
 
+ if (proc.to() && !err)
+ {
+ // Close the pipe, so that the SST process gets an EOF
+ proc.close_to();
+ }
+
 /* Inform server about SST script startup and release TO isolation */
  mysql_mutex_lock (&arg->lock);
  arg->err= -err;
  mysql_cond_signal (&arg->cond);
  mysql_mutex_unlock (&arg->lock); //! @note arg is unusable after that.
 
- if (proc.pipe() && !err)
+ if (proc.from() && !err)
  {
  long long total= 0;
  long long complete= 0;
  // total form previous stages
  long long total_prev= 0;
 
 wait_signal:
- out= my_fgets (out_buf, out_len, proc.pipe());
+ out= my_fgets (out_buf, out_len, proc.from());
 
  if (out)
  {