added queueing support

I have added queueing support so that when we read from the softsynth we
can put the text and commands we have read into a queue.  This will
allow us to retry calling espeak_synth() if we fill espeak's internal
buffer.

queue.c

@@ -0,0 +1,139 @@
+/*
+ *  espeakup - interface which allows speakup to use espeak
+ *
+ *  Copyright (C) 2008 William Hubbs
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *   This program is distributed in the hope that it will be useful,
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *   GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <assert.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "espeakup.h"
+
+struct queue_entry_t {
+	enum command_t cmd;
+	enum adjust_t adjust;
+	int value;
+	char *buf;
+	int len;
+	struct queue_entry_t *next;
+};
+
+static struct queue_entry_t *first = NULL;
+static struct queue_entry_t *last = NULL;
+
+static void queue_add(struct queue_entry_t *entry)
+{
+	assert(entry);
+	entry->next = NULL;
+	if (! last)
+		last = entry;
+	if (! first) {
+		first = entry;
+	} else {
+		first->next = entry;
+		first = first->next;
+	}
+}
+
+static void queue_remove(void)
+{
+	struct queue_entry_t *temp;
+
+	assert(last);
+	temp = last;
+	last = temp->next;
+	if (temp->cmd == CMD_SPEAK_TEXT)
+		free(temp->buf);
+	free(temp);
+	if (! last)
+		first = last;
+}
+
+void queue_clear(void)
+{
+	while(last)
+		queue_remove();
+}
+
+void queue_add_cmd(enum command_t cmd, enum adjust_t adj, int value)
+{
+	struct queue_entry_t *entry;
+
+	entry = malloc(sizeof(struct queue_entry_t));
+	if (! entry) {
+		perror("unable to allocate memory for queue entry");
+		return;
+	}
+	entry->cmd = cmd;
+	entry->adjust = adj;
+	entry->value = value;
+	queue_add(entry);
+}
+
+void queue_add_text(char *txt, size_t length)
+{
+	struct queue_entry_t *entry;
+
+	entry = malloc(sizeof(struct queue_entry_t));
+	if (! entry) {
+		perror("unable to allocate memory for queue entry");
+		return;
+	}
+	entry->cmd = CMD_SPEAK_TEXT;
+	entry->adjust = ADJ_SET;
+	entry->buf = strdup(txt);
+	if (! entry->buf) {
+		perror("unable to allocate space for text");
+		free(entry);
+		return;
+	}
+	entry->len = length;
+	queue_add(entry);
+}
+
+void queue_process_entry(struct synth_t *s)
+{
+	espeak_ERROR error;
+
+	if(! last)
+		return;
+
+	switch (last->cmd) {
+	case CMD_SET_FREQUENCY:
+		error = set_frequency(s, last->value, last->adjust);
+		break;
+	case CMD_SET_PITCH:
+		error = set_pitch(s, last->value, last->adjust);
+		break;
+	case CMD_SET_RATE:
+		error = set_rate(s, last->value, last->adjust);
+		break;
+	case CMD_SET_VOICE:
+		break;
+	case CMD_SET_VOLUME:
+		error = set_volume(s, last->value, last->adjust);
+		break;
+	case CMD_SPEAK_TEXT:
+		s->buf = last->buf;
+		s->len = last->len;
+		error = speak_text(s);
+		break;
+	}
+	if (error == EE_OK)
+		queue_remove();
+}