github.com/goplusjs/gopherjs@v1.2.6-0.20211206034512-f187917453b8/compiler/prelude/goroutines.go

package prelude

const goroutines = `
var $stackDepthOffset = 0;
var $getStackDepth = function() {
  var err = new Error();
  if (err.stack === undefined) {
    return undefined;
  }
  return $stackDepthOffset + err.stack.split("\n").length;
};

var $panicStackDepth = null, $panicValue;
var $callDeferred = function(deferred, jsErr, fromPanic) {
  if (!fromPanic && deferred !== null && deferred.index >= $curGoroutine.deferStack.length) {
    throw jsErr;
  }
  if (jsErr !== null) {
    var newErr = null;
    try {
      $curGoroutine.deferStack.push(deferred);
      $panic(new $jsErrorPtr(jsErr));
    } catch (err) {
      newErr = err;
    }
    $curGoroutine.deferStack.pop();
    $callDeferred(deferred, newErr);
    return;
  }
  if ($curGoroutine.asleep) {
    return;
  }

  $stackDepthOffset--;
  var outerPanicStackDepth = $panicStackDepth;
  var outerPanicValue = $panicValue;

  var localPanicValue = $curGoroutine.panicStack.pop();
  if (localPanicValue !== undefined) {
    $panicStackDepth = $getStackDepth();
    $panicValue = localPanicValue;
  }

  try {
    while (true) {
      if (deferred === null) {
        deferred = $curGoroutine.deferStack[$curGoroutine.deferStack.length - 1];
        if (deferred === undefined) {
          /* The panic reached the top of the stack. Clear it and throw it as a JavaScript error. */
          $panicStackDepth = null;
          if (localPanicValue.Object instanceof Error) {
            throw localPanicValue.Object;
          }
          var msg;
          if (localPanicValue.constructor === $String) {
            msg = localPanicValue.$val;
          } else if (localPanicValue.Error !== undefined) {
            msg = localPanicValue.Error();
          } else if (localPanicValue.String !== undefined) {
            msg = localPanicValue.String();
          } else {
            msg = localPanicValue;
          }
          throw new Error(msg);
        }
      }
      var call = deferred.pop();
      if (call === undefined) {
        $curGoroutine.deferStack.pop();
        if (localPanicValue !== undefined) {
          deferred = null;
          continue;
        }
        return;
      }
      var r = call[0].apply(call[2], call[1]);
      if (r && r.$blk !== undefined) {
        deferred.push([r.$blk, [], r]);
        if (fromPanic) {
          throw null;
        }
        return;
      }

      if (localPanicValue !== undefined && $panicStackDepth === null) {
        throw null; /* error was recovered */
      }
    }
  } finally {
    if (localPanicValue !== undefined) {
      if ($panicStackDepth !== null) {
        $curGoroutine.panicStack.push(localPanicValue);
      }
      $panicStackDepth = outerPanicStackDepth;
      $panicValue = outerPanicValue;
    }
    $stackDepthOffset++;
  }
};

var $panic = function(value) {
  $curGoroutine.panicStack.push(value);
  $callDeferred(null, null, true);
};
var $recover = function() {
  if ($panicStackDepth === null || ($panicStackDepth !== undefined && $panicStackDepth !== $getStackDepth() - 2)) {
    return $ifaceNil;
  }
  $panicStackDepth = null;
  return $panicValue;
};
var $throw = function(err) { throw err; };

var $noGoroutine = { asleep: false, exit: false, deferStack: [], panicStack: [] };
var $curGoroutine = $noGoroutine, $totalGoroutines = 0, $awakeGoroutines = 0, $checkForDeadlock = true;
var $mainFinished = false;
var $go = function(fun, args) {
  $totalGoroutines++;
  $awakeGoroutines++;
  var $goroutine = function() {
    try {
      $curGoroutine = $goroutine;
      var r = fun.apply(undefined, args);
      if (r && r.$blk !== undefined) {
        fun = function() { return r.$blk(); };
        args = [];
        return;
      }
      $goroutine.exit = true;
    } catch (err) {
      if (!$goroutine.exit) {
        throw err;
      }
    } finally {
      $curGoroutine = $noGoroutine;
      if ($goroutine.exit) { /* also set by runtime.Goexit() */
        $totalGoroutines--;
        $goroutine.asleep = true;
      }
      if ($goroutine.asleep) {
        $awakeGoroutines--;
        if (!$mainFinished && $awakeGoroutines === 0 && $checkForDeadlock) {
          console.error("fatal error: all goroutines are asleep - deadlock!");
          if ($global.process !== undefined) {
            $global.process.exit(2);
          }
        }
      }
    }
  };
  $goroutine.asleep = false;
  $goroutine.exit = false;
  $goroutine.deferStack = [];
  $goroutine.panicStack = [];
  $schedule($goroutine);
};

var $scheduled = [];
var $runScheduled = function() {
  try {
    var r;
    while ((r = $scheduled.shift()) !== undefined) {
      r();
    }
  } finally {
    if ($scheduled.length > 0) {
      setTimeout($runScheduled, 0);
    }
  }
};

var $schedule = function(goroutine) {
  if (goroutine.asleep) {
    goroutine.asleep = false;
    $awakeGoroutines++;
  }
  $scheduled.push(goroutine);
  if ($curGoroutine === $noGoroutine) {
    $runScheduled();
  }
};

var $setTimeout = function(f, t) {
  $awakeGoroutines++;
  return setTimeout(function() {
    $awakeGoroutines--;
    f();
  }, t);
};

var $block = function() {
  if ($curGoroutine === $noGoroutine) {
    $throwRuntimeError("cannot block in JavaScript callback, fix by wrapping code in goroutine");
  }
  $curGoroutine.asleep = true;
};

var $send = function(chan, value) {
  if (chan.$closed) {
    $throwRuntimeError("send on closed channel");
  }
  var queuedRecv = chan.$recvQueue.shift();
  if (queuedRecv !== undefined) {
    queuedRecv([value, true]);
    return;
  }
  if (chan.$buffer.length < chan.$capacity) {
    chan.$buffer.push(value);
    return;
  }

  var thisGoroutine = $curGoroutine;
  var closedDuringSend;
  chan.$sendQueue.push(function(closed) {
    closedDuringSend = closed;
    $schedule(thisGoroutine);
    return value;
  });
  $block();
  return {
    $blk: function() {
      if (closedDuringSend) {
        $throwRuntimeError("send on closed channel");
      }
    }
  };
};
var $recv = function(chan) {
  var queuedSend = chan.$sendQueue.shift();
  if (queuedSend !== undefined) {
    chan.$buffer.push(queuedSend(false));
  }
  var bufferedValue = chan.$buffer.shift();
  if (bufferedValue !== undefined) {
    return [bufferedValue, true];
  }
  if (chan.$closed) {
    return [chan.$elem.zero(), false];
  }

  var thisGoroutine = $curGoroutine;
  var f = { $blk: function() { return this.value; } };
  var queueEntry = function(v) {
    f.value = v;
    $schedule(thisGoroutine);
  };
  chan.$recvQueue.push(queueEntry);
  $block();
  return f;
};
var $close = function(chan) {
  if (chan.$closed) {
    $throwRuntimeError("close of closed channel");
  }
  chan.$closed = true;
  while (true) {
    var queuedSend = chan.$sendQueue.shift();
    if (queuedSend === undefined) {
      break;
    }
    queuedSend(true); /* will panic */
  }
  while (true) {
    var queuedRecv = chan.$recvQueue.shift();
    if (queuedRecv === undefined) {
      break;
    }
    queuedRecv([chan.$elem.zero(), false]);
  }
};
var $select = function(comms) {
  var ready = [];
  var selection = -1;
  for (var i = 0; i < comms.length; i++) {
    var comm = comms[i];
    var chan = comm[0];
    switch (comm.length) {
    case 0: /* default */
      selection = i;
      break;
    case 1: /* recv */
      if (chan.$sendQueue.length !== 0 || chan.$buffer.length !== 0 || chan.$closed) {
        ready.push(i);
      }
      break;
    case 2: /* send */
      if (chan.$closed) {
        $throwRuntimeError("send on closed channel");
      }
      if (chan.$recvQueue.length !== 0 || chan.$buffer.length < chan.$capacity) {
        ready.push(i);
      }
      break;
    }
  }

  if (ready.length !== 0) {
    selection = ready[Math.floor(Math.random() * ready.length)];
  }
  if (selection !== -1) {
    var comm = comms[selection];
    switch (comm.length) {
    case 0: /* default */
      return [selection];
    case 1: /* recv */
      return [selection, $recv(comm[0])];
    case 2: /* send */
      $send(comm[0], comm[1]);
      return [selection];
    }
  }

  var entries = [];
  var thisGoroutine = $curGoroutine;
  var f = { $blk: function() { return this.selection; } };
  var removeFromQueues = function() {
    for (var i = 0; i < entries.length; i++) {
      var entry = entries[i];
      var queue = entry[0];
      var index = queue.indexOf(entry[1]);
      if (index !== -1) {
        queue.splice(index, 1);
      }
    }
  };
  for (var i = 0; i < comms.length; i++) {
    (function(i) {
      var comm = comms[i];
      switch (comm.length) {
      case 1: /* recv */
        var queueEntry = function(value) {
          f.selection = [i, value];
          removeFromQueues();
          $schedule(thisGoroutine);
        };
        entries.push([comm[0].$recvQueue, queueEntry]);
        comm[0].$recvQueue.push(queueEntry);
        break;
      case 2: /* send */
        var queueEntry = function() {
          if (comm[0].$closed) {
            $throwRuntimeError("send on closed channel");
          }
          f.selection = [i];
          removeFromQueues();
          $schedule(thisGoroutine);
          return comm[1];
        };
        entries.push([comm[0].$sendQueue, queueEntry]);
        comm[0].$sendQueue.push(queueEntry);
        break;
      }
    })(i);
  }
  $block();
  return f;
};
`