Data commit

Task/Synchronous-concurrency/C/synchronous-concurrency.c

@@ -0,0 +1,112 @@
+#include <stdlib.h>	/* malloc(), realloc(), free() */
+#include <stdio.h>	/* fopen(), fgetc(), fwrite(), printf() */
+
+#include <libco.h>	/* co_create(), co_switch() */
+
+void
+fail(const char *message) {
+	perror(message);
+	exit(1);
+}
+
+/*
+ * These are global variables of this process. All cothreads of this
+ * process will share these global variables.
+ */
+cothread_t reader;
+cothread_t printer;
+struct {
+	char	*buf;	/* Not a C string. No terminating '\0'. */
+	size_t	len;	/* Length of line in buffer. */
+	size_t	cap;	/* Maximum capacity of buffer. */
+} line;
+size_t count;		/* Number of lines printed. */
+
+/*
+ * The reader cothread reads every line of an input file, passes each
+ * line to the printer cothread, and reports the number of lines.
+ */
+void
+reader_entry(void)
+{
+	FILE *input;
+	size_t newcap;
+	int c, eof, eol;
+	char *newbuf;
+
+	input = fopen("input.txt", "r");
+	if (input == NULL)
+		fail("fopen");
+
+	line.buf = malloc(line.cap = 4096);  /* New buffer. */
+	if (line.buf == NULL)
+		fail("malloc");
+	line.len = 0;  /* Start with an empty line. */
+
+	do {
+		c = fgetc(input);  /* Read next character. */
+		if (ferror(input))
+			fail("fgetc");
+
+		eof = (c == EOF);
+		if (eof) {
+			/*
+			 * End of file is also end of line,
+		`	 * unless the line would be empty.
+			 */
+			eol = (line.len > 0);
+		} else {
+			/* Append c to the buffer. */
+			if (line.len == line.cap) {
+				/* Need a bigger buffer! */
+				newcap = line.cap * 2;
+				newbuf = realloc(line.buf, newcap);
+				if (newbuf == NULL)
+					fail("realloc");
+				line.buf = newbuf;
+				line.cap = newcap;
+			}
+			line.buf[line.len++] = c;
+
+			/* '\n' is end of line. */
+			eol = (c == '\n');
+		}
+
+		if (eol) {
+			/* Pass our complete line to the printer. */
+			co_switch(printer);
+			line.len = 0;  /* Destroy our line. */
+		}
+	} while (!eof);
+
+	free(line.buf);
+	line.buf = NULL;  /* Stops a loop in the printer. */
+
+	printf("Printed %zu lines.\n", count);
+	co_switch(printer);
+}
+
+/*
+ * The printer cothread starts the reader cothread, prints every line
+ * line from the reader cothread, and counts the number of lines.
+ */
+int
+main()
+{
+	reader = co_create(4096, reader_entry);
+	printer = co_active();
+	count = 0;
+
+	for (;;) {
+		co_switch(reader);
+		if (line.buf == NULL)
+			break;
+
+		/* Print this line. Count it. */
+		fwrite(line.buf, 1, line.len, stdout);
+		count++;
+	}
+
+	co_delete(reader);
+	return 0;
+}