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memblockq-test: fix incorrect assumption of pa_memblockq_pop_missing() behaviour

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The intuitive meaning of "missing" would be the difference between
tlength and the current queue length, and that's how memblockq-test
assumed pa_memblockq_pop_missing() to define the term "missing", but
that was an incorrect assumption, causing the last
pa_memblockq_pop_missing() return value assertion to fail.

This patch fixes the failing assertion and adds some comments about how
the "missing" and "requested" variables in memblockq work.
This commit is contained in:
Tanu Kaskinen 2016-12-30 17:52:36 +02:00
parent 8e9f070747
commit b6e6e78cc2
1 changed files with 75 additions and 20 deletions
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95
src/tests/memblockq-test.c
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@ -421,74 +421,129 @@ START_TEST (memblockq_test_pop_missing) {
bq = pa_memblockq_new("test memblockq", idx, maxlength, tlength, &ss, prebuf, minreq, maxrewind, &silence);
fail_unless(bq != NULL);
/* initially, the whole target length of bytes is missing */
/* The following equation regarding the internal variables of a memblockq
* is always true:
*
* length + missing + requested = tlength
*
* "length" is the current memblockq length (write index minus read index)
* and "tlength" is the target length. The intuitive meaning of "missing"
* would be the difference between tlength and length, but actually
* "missing" and "requested" together constitute the amount that is missing
* from the queue. Writing to the queue decrements "requested" and reading
* from the queue increments "missing". pa_memblockq_pop_missing() resets
* "missing" to zero, returns the old "missing" value and adds the
* equivalent amount to "requested".
*
* This test has comments between each step documenting the assumed state
* of those internal variables. */
/* length + missing + requested = tlength
* 0 + 100 + 0 = 100 */
ck_assert_int_eq(pa_memblockq_pop_missing(bq), tlength);
/* add 20 bytes of data */
/* length + missing + requested = tlength
* 0 + 0 + 100 = 100 */
for (int i = 0; i != 2; ++i)
ck_assert_int_eq(pa_memblockq_push(bq, &data), 0);
check_queue_invariants(bq);
/* no new missing data is reported */
/* length + missing + requested = tlength
* 20 + 0 + 80 = 100 */
ck_assert_int_eq(pa_memblockq_pop_missing(bq), 0);
/* fill up to 100 bytes of data */
/* length + missing + requested = tlength
* 20 + 0 + 80 = 100 */
for (int i = 0; i != 8; ++i)
ck_assert_int_eq(pa_memblockq_push(bq, &data), 0);
check_queue_invariants(bq);
/* queue fill level is at target level now */
/* length + missing + requested = tlength
* 100 + 0 + 0 = 100 */
ck_assert_int_eq(pa_memblockq_pop_missing(bq), 0);
/* pop 40 bytes of data, down to 60 bytes fill level */
/* length + missing + requested = tlength
* 100 + 0 + 0 = 100 */
ck_assert_int_eq(pa_memblockq_peek_fixed_size(bq, 40, &chunk), 0);
pa_memblockq_drop(bq, 40);
ck_assert_int_eq(chunk.length - chunk.index, 40);
pa_memblock_unref(chunk.memblock);
check_queue_invariants(bq);
/* queue fill level is 40 bytes under target length
* This is less than minreq, so no missing data is reported */
/* length + missing + requested = tlength
* 60 + 40 + 0 = 100 */
/* 40 bytes are missing, but that's less than minreq, so 0 is reported */
ck_assert_int_eq(pa_memblockq_pop_missing(bq), 0);
/* add 30 bytes of data, up to 90 bytes fill level */
/* length + missing + requested = tlength
* 60 + 40 + 0 = 100 */
/* Now we push 30 bytes even though it was not requested, so the requested
* counter goes negative! */
for (int i = 0; i != 3; ++i)
ck_assert_int_eq(pa_memblockq_push(bq, &data), 0);
check_queue_invariants(bq);
/* queue fill level is 10 bytes under target length
* This is less than minreq, so no missing data is reported. */
/* length + missing + requested = tlength
* 90 + 40 + -30 = 100 */
/* missing < minreq, so nothing is reported missing. */
ck_assert_int_eq(pa_memblockq_pop_missing(bq), 0);
/* pop 20 bytes of data, down to 70 bytes of data */
/* length + missing + requested = tlength
* 90 + 40 + -30 = 100 */
ck_assert_int_eq(pa_memblockq_peek_fixed_size(bq, 20, &chunk), 0);
pa_memblockq_drop(bq, 20);
ck_assert_int_eq(chunk.length - chunk.index, 20);
pa_memblock_unref(chunk.memblock);
check_queue_invariants(bq);
/* queue fill level is 30 bytes under target length
* This is less than minreq, so no missing data is reported */
/* length + missing + requested = tlength
* 70 + 60 + -30 = 100 */
/* missing < minreq, so nothing is reported missing. */
ck_assert_int_eq(pa_memblockq_pop_missing(bq), 0);
/* add 50 bytes of data, up to 120 bytes fill level */
/* length + missing + requested = tlength
* 70 + 60 + -30 = 100 */
/* We push more data again even though it was not requested, so the
* requested counter goes further into the negative range. */
for (int i = 0; i != 5; ++i)
ck_assert_int_eq(pa_memblockq_push(bq, &data), 0);
check_queue_invariants(bq);
/* queue fill level is above target level, so no missing data is reported. */
/* length + missing + requested = tlength
* 120 + 60 + -80 = 100 */
/* missing < minreq, so nothing is reported missing. */
ck_assert_int_eq(pa_memblockq_pop_missing(bq), 0);
/* pop 20 bytes of data, down the target level */
/* length + missing + requested = tlength
* 120 + 60 + -80 = 100 */
ck_assert_int_eq(pa_memblockq_peek_fixed_size(bq, 20, &chunk), 0);
pa_memblockq_drop(bq, 20);
ck_assert_int_eq(chunk.length - chunk.index, 20);
pa_memblock_unref(chunk.memblock);
check_queue_invariants(bq);
/* queue fill level is at target level now
* No missing data should be reported. */
ck_assert_int_eq(pa_memblockq_pop_missing(bq), 0);
/* length + missing + requested = tlength
* 100 + 80 + -80 = 100 */
/* missing has now reached the minreq threshold */
ck_assert_int_eq(pa_memblockq_pop_missing(bq), 80);
/* length + missing + requested = tlength
* 100 + 0 + 0 = 100 */
/* cleanup */
pa_memblockq_free(bq);