src/core/client_config/lb_policies/pick_first.c

/*
 *
 * Copyright 2015, Google Inc.
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 * modification, are permitted provided that the following conditions are
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 *
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 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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#include "src/core/client_config/lb_policy_factory.h"
#include "src/core/client_config/lb_policies/pick_first.h"

#include <string.h>

#include <grpc/support/alloc.h>
#include "src/core/transport/connectivity_state.h"

typedef struct pending_pick
{
  struct pending_pick *next;
  grpc_pollset *pollset;
  grpc_subchannel **target;
  grpc_closure *on_complete;
} pending_pick;

typedef struct
{
  /** base policy: must be first */
  grpc_lb_policy base;
  /** all our subchannels */
  grpc_subchannel **subchannels;
  size_t num_subchannels;

  grpc_closure connectivity_changed;

  /** mutex protecting remaining members */
  gpr_mu mu;
  /** the selected channel
      TODO(ctiller): this should be atomically set so we don't
                     need to take a mutex in the common case */
  grpc_subchannel *selected;
  /** have we started picking? */
  int started_picking;
  /** are we shut down? */
  int shutdown;
  /** which subchannel are we watching? */
  size_t checking_subchannel;
  /** what is the connectivity of that channel? */
  grpc_connectivity_state checking_connectivity;
  /** list of picks that are waiting on connectivity */
  pending_pick *pending_picks;

  /** our connectivity state tracker */
  grpc_connectivity_state_tracker state_tracker;
} pick_first_lb_policy;

static void
del_interested_parties_locked (pick_first_lb_policy * p, grpc_closure_list * closure_list)
{
  pending_pick *pp;
  for (pp = p->pending_picks; pp; pp = pp->next)
    {
      grpc_subchannel_del_interested_party (p->subchannels[p->checking_subchannel], pp->pollset, closure_list);
    }
}

static void
add_interested_parties_locked (pick_first_lb_policy * p, grpc_closure_list * closure_list)
{
  pending_pick *pp;
  for (pp = p->pending_picks; pp; pp = pp->next)
    {
      grpc_subchannel_add_interested_party (p->subchannels[p->checking_subchannel], pp->pollset, closure_list);
    }
}

void
pf_destroy (grpc_lb_policy * pol, grpc_closure_list * closure_list)
{
  pick_first_lb_policy *p = (pick_first_lb_policy *) pol;
  size_t i;
  GPR_ASSERT (p->pending_picks == NULL);
  for (i = 0; i < p->num_subchannels; i++)
    {
      GRPC_SUBCHANNEL_UNREF (p->subchannels[i], "pick_first", closure_list);
    }
  grpc_connectivity_state_destroy (&p->state_tracker, closure_list);
  gpr_free (p->subchannels);
  gpr_mu_destroy (&p->mu);
  gpr_free (p);
}

void
pf_shutdown (grpc_lb_policy * pol, grpc_closure_list * closure_list)
{
  pick_first_lb_policy *p = (pick_first_lb_policy *) pol;
  pending_pick *pp;
  gpr_mu_lock (&p->mu);
  del_interested_parties_locked (p, closure_list);
  p->shutdown = 1;
  pp = p->pending_picks;
  p->pending_picks = NULL;
  grpc_connectivity_state_set (&p->state_tracker, GRPC_CHANNEL_FATAL_FAILURE, "shutdown", closure_list);
  gpr_mu_unlock (&p->mu);
  while (pp != NULL)
    {
      pending_pick *next = pp->next;
      *pp->target = NULL;
      grpc_closure_list_add (closure_list, pp->on_complete, 1);
      gpr_free (pp);
      pp = next;
    }
}

static void
start_picking (pick_first_lb_policy * p, grpc_closure_list * closure_list)
{
  p->started_picking = 1;
  p->checking_subchannel = 0;
  p->checking_connectivity = GRPC_CHANNEL_IDLE;
  GRPC_LB_POLICY_REF (&p->base, "pick_first_connectivity");
  grpc_subchannel_notify_on_state_change (p->subchannels[p->checking_subchannel], &p->checking_connectivity, &p->connectivity_changed, closure_list);
}

void
pf_exit_idle (grpc_lb_policy * pol, grpc_closure_list * closure_list)
{
  pick_first_lb_policy *p = (pick_first_lb_policy *) pol;
  gpr_mu_lock (&p->mu);
  if (!p->started_picking)
    {
      start_picking (p, closure_list);
    }
  gpr_mu_unlock (&p->mu);
}

void
pf_pick (grpc_lb_policy * pol, grpc_pollset * pollset, grpc_metadata_batch * initial_metadata, grpc_subchannel ** target, grpc_closure * on_complete, grpc_closure_list * closure_list)
{
  pick_first_lb_policy *p = (pick_first_lb_policy *) pol;
  pending_pick *pp;
  gpr_mu_lock (&p->mu);
  if (p->selected)
    {
      gpr_mu_unlock (&p->mu);
      *target = p->selected;
      grpc_closure_list_add (closure_list, on_complete, 1);
    }
  else
    {
      if (!p->started_picking)
	{
	  start_picking (p, closure_list);
	}
      grpc_subchannel_add_interested_party (p->subchannels[p->checking_subchannel], pollset, closure_list);
      pp = gpr_malloc (sizeof (*pp));
      pp->next = p->pending_picks;
      pp->pollset = pollset;
      pp->target = target;
      pp->on_complete = on_complete;
      p->pending_picks = pp;
      gpr_mu_unlock (&p->mu);
    }
}

static void
pf_connectivity_changed (void *arg, int iomgr_success, grpc_closure_list * closure_list)
{
  pick_first_lb_policy *p = arg;
  pending_pick *pp;

  gpr_mu_lock (&p->mu);

  if (p->shutdown)
    {
      gpr_mu_unlock (&p->mu);
      GRPC_LB_POLICY_UNREF (&p->base, "pick_first_connectivity", closure_list);
      return;
    }
  else if (p->selected != NULL)
    {
      grpc_connectivity_state_set (&p->state_tracker, p->checking_connectivity, "selected_changed", closure_list);
      if (p->checking_connectivity != GRPC_CHANNEL_FATAL_FAILURE)
	{
	  grpc_subchannel_notify_on_state_change (p->selected, &p->checking_connectivity, &p->connectivity_changed, closure_list);
	}
      else
	{
	  GRPC_LB_POLICY_UNREF (&p->base, "pick_first_connectivity", closure_list);
	}
    }
  else
    {
    loop:
      switch (p->checking_connectivity)
	{
	case GRPC_CHANNEL_READY:
	  grpc_connectivity_state_set (&p->state_tracker, GRPC_CHANNEL_READY, "connecting_ready", closure_list);
	  p->selected = p->subchannels[p->checking_subchannel];
	  while ((pp = p->pending_picks))
	    {
	      p->pending_picks = pp->next;
	      *pp->target = p->selected;
	      grpc_subchannel_del_interested_party (p->selected, pp->pollset, closure_list);
	      grpc_closure_list_add (closure_list, pp->on_complete, 1);
	      gpr_free (pp);
	    }
	  grpc_subchannel_notify_on_state_change (p->selected, &p->checking_connectivity, &p->connectivity_changed, closure_list);
	  break;
	case GRPC_CHANNEL_TRANSIENT_FAILURE:
	  grpc_connectivity_state_set (&p->state_tracker, GRPC_CHANNEL_TRANSIENT_FAILURE, "connecting_transient_failure", closure_list);
	  del_interested_parties_locked (p, closure_list);
	  p->checking_subchannel = (p->checking_subchannel + 1) % p->num_subchannels;
	  p->checking_connectivity = grpc_subchannel_check_connectivity (p->subchannels[p->checking_subchannel]);
	  add_interested_parties_locked (p, closure_list);
	  if (p->checking_connectivity == GRPC_CHANNEL_TRANSIENT_FAILURE)
	    {
	      grpc_subchannel_notify_on_state_change (p->subchannels[p->checking_subchannel], &p->checking_connectivity, &p->connectivity_changed, closure_list);
	    }
	  else
	    {
	      goto loop;
	    }
	  break;
	case GRPC_CHANNEL_CONNECTING:
	case GRPC_CHANNEL_IDLE:
	  grpc_connectivity_state_set (&p->state_tracker, GRPC_CHANNEL_CONNECTING, "connecting_changed", closure_list);
	  grpc_subchannel_notify_on_state_change (p->subchannels[p->checking_subchannel], &p->checking_connectivity, &p->connectivity_changed, closure_list);
	  break;
	case GRPC_CHANNEL_FATAL_FAILURE:
	  del_interested_parties_locked (p, closure_list);
	  GPR_SWAP (grpc_subchannel *, p->subchannels[p->checking_subchannel], p->subchannels[p->num_subchannels - 1]);
	  p->num_subchannels--;
	  GRPC_SUBCHANNEL_UNREF (p->subchannels[p->num_subchannels], "pick_first", closure_list);
	  if (p->num_subchannels == 0)
	    {
	      grpc_connectivity_state_set (&p->state_tracker, GRPC_CHANNEL_FATAL_FAILURE, "no_more_channels", closure_list);
	      while ((pp = p->pending_picks))
		{
		  p->pending_picks = pp->next;
		  *pp->target = NULL;
		  grpc_closure_list_add (closure_list, pp->on_complete, 1);
		  gpr_free (pp);
		}
	      GRPC_LB_POLICY_UNREF (&p->base, "pick_first_connectivity", closure_list);
	    }
	  else
	    {
	      grpc_connectivity_state_set (&p->state_tracker, GRPC_CHANNEL_TRANSIENT_FAILURE, "subchannel_failed", closure_list);
	      p->checking_subchannel %= p->num_subchannels;
	      p->checking_connectivity = grpc_subchannel_check_connectivity (p->subchannels[p->checking_subchannel]);
	      add_interested_parties_locked (p, closure_list);
	      goto loop;
	    }
	}
    }

  gpr_mu_unlock (&p->mu);
}

static void
pf_broadcast (grpc_lb_policy * pol, grpc_transport_op * op, grpc_closure_list * closure_list)
{
  pick_first_lb_policy *p = (pick_first_lb_policy *) pol;
  size_t i;
  size_t n;
  grpc_subchannel **subchannels;

  gpr_mu_lock (&p->mu);
  n = p->num_subchannels;
  subchannels = gpr_malloc (n * sizeof (*subchannels));
  for (i = 0; i < n; i++)
    {
      subchannels[i] = p->subchannels[i];
      GRPC_SUBCHANNEL_REF (subchannels[i], "pf_broadcast");
    }
  gpr_mu_unlock (&p->mu);

  for (i = 0; i < n; i++)
    {
      grpc_subchannel_process_transport_op (subchannels[i], op, closure_list);
      GRPC_SUBCHANNEL_UNREF (subchannels[i], "pf_broadcast", closure_list);
    }
  gpr_free (subchannels);
}

static grpc_connectivity_state
pf_check_connectivity (grpc_lb_policy * pol, grpc_closure_list * closure_list)
{
  pick_first_lb_policy *p = (pick_first_lb_policy *) pol;
  grpc_connectivity_state st;
  gpr_mu_lock (&p->mu);
  st = grpc_connectivity_state_check (&p->state_tracker);
  gpr_mu_unlock (&p->mu);
  return st;
}

void
pf_notify_on_state_change (grpc_lb_policy * pol, grpc_connectivity_state * current, grpc_closure * notify, grpc_closure_list * closure_list)
{
  pick_first_lb_policy *p = (pick_first_lb_policy *) pol;
  gpr_mu_lock (&p->mu);
  grpc_connectivity_state_notify_on_state_change (&p->state_tracker, current, notify, closure_list);
  gpr_mu_unlock (&p->mu);
}

static const grpc_lb_policy_vtable pick_first_lb_policy_vtable = {
  pf_destroy,
  pf_shutdown,
  pf_pick,
  pf_exit_idle,
  pf_broadcast,
  pf_check_connectivity,
  pf_notify_on_state_change
};

static void
pick_first_factory_ref (grpc_lb_policy_factory * factory)
{
}

static void
pick_first_factory_unref (grpc_lb_policy_factory * factory)
{
}

static grpc_lb_policy *
create_pick_first (grpc_lb_policy_factory * factory, grpc_lb_policy_args * args)
{
  pick_first_lb_policy *p = gpr_malloc (sizeof (*p));
  GPR_ASSERT (args->num_subchannels > 0);
  memset (p, 0, sizeof (*p));
  grpc_lb_policy_init (&p->base, &pick_first_lb_policy_vtable);
  p->subchannels = gpr_malloc (sizeof (grpc_subchannel *) * args->num_subchannels);
  p->num_subchannels = args->num_subchannels;
  grpc_connectivity_state_init (&p->state_tracker, GRPC_CHANNEL_IDLE, "pick_first");
  memcpy (p->subchannels, args->subchannels, sizeof (grpc_subchannel *) * args->num_subchannels);
  grpc_closure_init (&p->connectivity_changed, pf_connectivity_changed, p);
  gpr_mu_init (&p->mu);
  return &p->base;
}

static const grpc_lb_policy_factory_vtable pick_first_factory_vtable = {
  pick_first_factory_ref, pick_first_factory_unref, create_pick_first,
  "pick_first"
};

static grpc_lb_policy_factory pick_first_lb_policy_factory = {
  &pick_first_factory_vtable
};

grpc_lb_policy_factory *
grpc_pick_first_lb_factory_create ()
{
  return &pick_first_lb_policy_factory;
}