libgo/runtime/go-rec-nb-small.c

   1 /* go-rec-nb-small.c -- nonblocking receive of something smal on a channel.
   2
   3    Copyright 2009 The Go Authors. All rights reserved.
   4    Use of this source code is governed by a BSD-style
   5    license that can be found in the LICENSE file.  */
   6
   7 #include <stdint.h>
   8
   9 #include "go-assert.h"
  10 #include "go-panic.h"
  11 #include "channel.h"
  12
  13 /* Prepare to receive something on a nonblocking channel.  */
  14
  15 int
  16 __go_receive_nonblocking_acquire (struct __go_channel *channel)
  17 {
  18   int i;
  19   _Bool has_data;
  20
  21   i = pthread_mutex_lock (&channel->lock);
  22   __go_assert (i == 0);
  23
  24   while (channel->selected_for_receive)
  25     {
  26       i = pthread_cond_wait (&channel->cond, &channel->lock);
  27       __go_assert (i == 0);
  28     }
  29
  30   if (channel->is_closed
  31       && (channel->num_entries == 0
  32           ? channel->next_store == 0
  33           : channel->next_fetch == channel->next_store))
  34     {
  35       __go_unlock_and_notify_selects (channel);
  36       return RECEIVE_NONBLOCKING_ACQUIRE_CLOSED;
  37     }
  38
  39   if (channel->num_entries > 0)
  40     has_data = channel->next_fetch != channel->next_store;
  41   else
  42     {
  43       if (channel->waiting_to_receive)
  44         {
  45           /* Some other goroutine is already waiting for data on this
  46              channel, so we can't pick it up.  */
  47           has_data = 0;
  48         }
  49       else if (channel->next_store > 0)
  50         {
  51           /* There is data on the channel.  */
  52           has_data = 1;
  53         }
  54       else if (__go_synch_with_select (channel, 0))
  55         {
  56           /* We synched up with a select sending data, so there will
  57              be data for us shortly.  Tell the select to go, and then
  58              wait for the data.  */
  59           __go_broadcast_to_select (channel);
  60
  61           while (channel->next_store == 0)
  62             {
  63               i = pthread_cond_wait (&channel->cond, &channel->lock);
  64               __go_assert (i == 0);
  65             }
  66
  67           has_data = 1;
  68         }
  69       else
  70         {
  71           /* Otherwise there is no data.  */
  72           has_data = 0;
  73         }
  74
  75       if (has_data)
  76         {
  77           channel->waiting_to_receive = 1;
  78           __go_assert (channel->next_store == 1);
  79         }
  80     }
  81
  82   if (!has_data)
  83     {
  84       i = pthread_mutex_unlock (&channel->lock);
  85       __go_assert (i == 0);
  86       return RECEIVE_NONBLOCKING_ACQUIRE_NODATA;
  87     }
  88
  89   return RECEIVE_NONBLOCKING_ACQUIRE_DATA;
  90 }
  91
  92 /* Receive something 64 bits or smaller on a nonblocking channel.  */
  93
  94 struct __go_receive_nonblocking_small
  95 __go_receive_nonblocking_small (struct __go_channel *channel)
  96 {
  97   uintptr_t element_size;
  98   struct __go_receive_nonblocking_small ret;
  99
 100   element_size = channel->element_type->__size;
 101   __go_assert (element_size <= sizeof (uint64_t));
 102
 103   int data = __go_receive_nonblocking_acquire (channel);
 104   if (data != RECEIVE_NONBLOCKING_ACQUIRE_DATA)
 105     {
 106       ret.__val = 0;
 107       ret.__success = 0;
 108       ret.__closed = data == RECEIVE_NONBLOCKING_ACQUIRE_CLOSED;
 109       return ret;
 110     }
 111
 112   ret.__val = channel->data[channel->next_fetch];
 113
 114   __go_receive_release (channel);
 115
 116   ret.__success = 1;
 117   ret.__closed = 0;
 118
 119   return ret;
 120 }