make synchronous "exists" method keep the event loop alive

generic/zookeepertcl.c

@@ -1096,8 +1096,6 @@ zootcl_exists_subcommand(Tcl_Interp *interp, int objc, Tcl_Obj *CONST objv[], ZO
 
  const char *path;
  watcher_fn wfn = NULL;
- struct Stat *stat = NULL;
- struct Stat statBuf;
 
  assert (zo->zookeeper_object_magic == ZOOKEEPER_OBJECT_MAGIC);
 
@@ -1151,7 +1149,6 @@ zootcl_exists_subcommand(Tcl_Interp *interp, int objc, Tcl_Obj *CONST objv[], ZO
  return TCL_ERROR;
  }
  statArray = Tcl_GetString (objv[++i]);
- stat = &statBuf;
  break;
  }
 
@@ -1162,7 +1159,6 @@ zootcl_exists_subcommand(Tcl_Interp *interp, int objc, Tcl_Obj *CONST objv[], ZO
  return TCL_ERROR;
  }
  versionVarObj = objv[++i];
- stat = &statBuf;
  break;
  }
  }
@@ -1187,31 +1183,69 @@ zootcl_exists_subcommand(Tcl_Interp *interp, int objc, Tcl_Obj *CONST objv[], ZO
  int status;
 
  if (asyncCallbackObj == NULL) {
- // do the synchronous version of wexists
- status = zoo_wexists (zh, path, wfn, (void *)watcherCallbackObj, stat);
+ // synchronous request
+ // invoke the special async handler for sync requests
+ // so the event loop will still be alive
+ zootcl_syncCallbackContext *zsc = (zootcl_syncCallbackContext *)ckalloc (sizeof (zootcl_syncCallbackContext));
+ zsc->zo = zo;
+ zsc->syncDone = 0;
+ status = zoo_awexists (zh, path, wfn, (void *)watcherCallbackObj, zootcl_sync_stat_completion_callback, zsc);
+ // handle errors from the call like bad arguments and stuff
+ if (status != ZOK) {
+ ckfree (zsc);
+ return zootcl_set_tcl_return_code (interp, status);
+ }
+
+ // wait with the tcl loop alive until the sync callback sets
+ // the syncDone flag in the sync callback context asc
+ if (zootcl_wait (zo, zsc) == TCL_ERROR) {
+ return TCL_ERROR;
+ }
+
+ // ok, we got our zsc filled up, if the status isn't OK,
+ // error out
+ status = zsc->rc;
+
+ // if there's no node hand that according to our rule.
+ // unset the version var since we don't have one and we
+ // don't want to confuse the caller by letting through some
+ // old thing or require them to unset the var before calling
+ // us. that ain't happenin'.
  if (status == ZNONODE) {
  if (versionVarObj != NULL) {
  Tcl_UnsetVar (interp, Tcl_GetString (versionVarObj), 0);
  }
  Tcl_SetObjResult (interp, Tcl_NewBooleanObj (0));
+ ckfree (zsc);
  return TCL_OK;
  }
 
+ // ok anything other than ZOK is now an error (ZNONODE we
+ // handled specially, above.)
  if (status != ZOK) {
+ ckfree (zsc);
  return zootcl_set_tcl_return_code (interp, status);
  }
 
+ // it does exist
  Tcl_SetObjResult (interp, Tcl_NewBooleanObj (1));
 
- if (statArray != NULL && zootcl_stat_to_array (interp, statArray, stat) == TCL_ERROR) {
+ // if the caller wanted a stat array, we're good here,
+ // fill that.
+ if (statArray != NULL && zootcl_stat_to_array (interp, statArray, &zsc->stat) == TCL_ERROR) {
+ ckfree (zsc);
  return TCL_ERROR;
  }
 
+ // we want version so commonly and not much else in the stat array
+ // so we have a -version option to make it easy
  if (versionVarObj != NULL) {
- if (Tcl_SetVar2Ex (interp, Tcl_GetString (versionVarObj), NULL, Tcl_NewIntObj (stat->version), TCL_LEAVE_ERR_MSG) == NULL) {
+ if (Tcl_SetVar2Ex (interp, Tcl_GetString (versionVarObj), NULL, Tcl_NewIntObj (zsc->stat.version), TCL_LEAVE_ERR_MSG) == NULL) {
+ ckfree (zsc);
  return TCL_ERROR;
  }
  }
+ ckfree (zsc);
  } else {
  // do the asynchronous version of znode existence check
  zootcl_callbackContext *ztc = (zootcl_callbackContext *)ckalloc (sizeof (zootcl_callbackContext));