Fix a bug in base-log, and add test.

The tests compute usable space in the log, but do so using subtraction on unsigned values and did not correctly account for number of blocks used per-core. This could lead underflow, and an incorrect space calculation.

In addition, testing showed that with current defaults, tests would fail on a system with > ~64 cores. This can be alleviated through use of a larger log. An explicit
check in the log initialization has been added for this case, and the log size increased if necessary.
	Change on 2014/12/15 by aveitch <aveitch@google.com>
-------------
Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=82154432

build.json

@@ -821,6 +821,18 @@
         "gpr"
       ]
     },
+    {
+      "name": "census_statistics_small_log_test",
+      "build": "test",
+      "src": [
+        "test/core/statistics/small_log_test.c"
+      ],
+      "deps": [
+        "grpc_test_util",
+        "grpc",
+        "gpr"
+      ]
+    },
     {
       "name": "census_statistics_performance_test",
       "build": "test",

src/core/statistics/census_log.c

@@ -97,6 +97,7 @@
 #include <grpc/support/log.h>
 #include <grpc/support/port_platform.h>
 #include <grpc/support/sync.h>
+#include <grpc/support/useful.h>
 
 /* End of platform specific code */
 
@@ -118,7 +119,7 @@ typedef struct census_log_block {
   gpr_int32 bytes_read;
   /* Links for list */
   cl_block_list_struct link;
-  /* We want this structure to be cacheline aligned. We assume the following
+/* We want this structure to be cacheline aligned. We assume the following
    sizes for the various parts on 32/64bit systems:
    type                 32b size    64b size
    char*                   4           8
@@ -154,7 +155,7 @@ typedef struct census_log_block_list {
    be initialized via set_block(), before calling other functions */
 typedef struct census_log_core_local_block {
   gpr_atm block;
-  /* Ensure cachline alignment: we assume sizeof(gpr_atm) == 4 or 8 */
+/* Ensure cachline alignment: we assume sizeof(gpr_atm) == 4 or 8 */
 #if defined(GPR_ARCH_64)
 #define CL_CORE_LOCAL_BLOCK_PAD_SIZE (GPR_CACHELINE_SIZE - 8)
 #else
@@ -200,14 +201,9 @@ static struct census_log g_log;
 /* Functions that operate on an atomic memory location used as a lock */
 
 /* Returns non-zero if lock is acquired */
-static int cl_try_lock(gpr_atm* lock) {
-  return gpr_atm_acq_cas(lock, 0, 1);
-}
-
-static void cl_unlock(gpr_atm* lock) {
-  gpr_atm_rel_store(lock, 0);
-}
+static int cl_try_lock(gpr_atm* lock) { return gpr_atm_acq_cas(lock, 0, 1); }
 
+static void cl_unlock(gpr_atm* lock) { gpr_atm_rel_store(lock, 0); }
 
 /* Functions that operate on cl_core_local_block's */
 
@@ -220,7 +216,6 @@ static cl_block* cl_core_local_block_get_block(cl_core_local_block* clb) {
   return (cl_block*)gpr_atm_acq_load(&clb->block);
 }
 
-
 /* Functions that operate on cl_block_list_struct's */
 
 static void cl_block_list_struct_initialize(cl_block_list_struct* bls,
@@ -229,7 +224,6 @@ static void cl_block_list_struct_initialize(cl_block_list_struct* bls,
   bls->block = block;
 }
 
-
 /* Functions that operate on cl_block_list's */
 
 static void cl_block_list_initialize(cl_block_list* list) {
@@ -243,8 +237,7 @@ static cl_block* cl_block_list_head(cl_block_list* list) {
 }
 
 /* Insert element *e after *pos. */
-static void cl_block_list_insert(cl_block_list* list,
-                                 cl_block_list_struct* pos,
+static void cl_block_list_insert(cl_block_list* list, cl_block_list_struct* pos,
                                  cl_block_list_struct* e) {
   list->count++;
   e->next = pos->next;
@@ -254,14 +247,12 @@ static void cl_block_list_insert(cl_block_list* list,
 }
 
 /* Insert block at the head of the list */
-static void cl_block_list_insert_at_head(cl_block_list* list,
-                                         cl_block* block) {
+static void cl_block_list_insert_at_head(cl_block_list* list, cl_block* block) {
   cl_block_list_insert(list, &list->ht, &block->link);
 }
 
 /* Insert block at the tail of the list */
-static void cl_block_list_insert_at_tail(cl_block_list* list,
-                                         cl_block* block) {
+static void cl_block_list_insert_at_tail(cl_block_list* list, cl_block* block) {
   cl_block_list_insert(list, list->ht.prev, &block->link);
 }
 
@@ -272,7 +263,6 @@ static void cl_block_list_remove(cl_block_list* list, cl_block* b) {
   b->link.prev->next = b->link.next;
 }
 
-
 /* Functions that operate on cl_block's */
 
 static void cl_block_initialize(cl_block* block, char* buffer) {
@@ -374,7 +364,6 @@ static void cl_block_end_read(cl_block* block) {
   cl_unlock(&block->reader_lock);
 }
 
-
 /* Internal functions operating on g_log */
 
 /* Allocates a new free block (or recycles an available dirty block if log is
@@ -472,17 +461,15 @@ static cl_block* cl_next_block_to_read(cl_block* prev) {
 /* External functions: primary stats_log interface */
 void census_log_initialize(size_t size_in_mb, int discard_old_records) {
   gpr_int32 ix;
-  /* check cacheline alignment */
+  /* Check cacheline alignment. */
   GPR_ASSERT(sizeof(cl_block) % GPR_CACHELINE_SIZE == 0);
   GPR_ASSERT(sizeof(cl_core_local_block) % GPR_CACHELINE_SIZE == 0);
   GPR_ASSERT(!g_log.initialized);
   g_log.discard_old_records = discard_old_records;
   g_log.num_cores = gpr_cpu_num_cores();
-  if (size_in_mb < 1 || size_in_mb > 1000) {
-    gpr_log(GPR_ERROR, "Invalid size for stats_log: using 1MB default");
-    size_in_mb = 1;
-  }
-  g_log.num_blocks = (size_in_mb << 20) >> CENSUS_LOG_2_MAX_RECORD_SIZE;
+  /* Ensure at least as many blocks as there are cores. */
+  g_log.num_blocks = GPR_MAX(
+      g_log.num_cores, (size_in_mb << 20) >> CENSUS_LOG_2_MAX_RECORD_SIZE);
   gpr_mu_init(&g_log.lock);
   g_log.read_iterator_state = 0;
   g_log.block_being_read = NULL;
@@ -585,8 +572,8 @@ const void* census_log_read_next(size_t* bytes_available) {
   do {
     g_log.block_being_read = cl_next_block_to_read(g_log.block_being_read);
     if (g_log.block_being_read != NULL) {
-      void* record = cl_block_start_read(g_log.block_being_read,
-                                          bytes_available);
+      void* record =
+          cl_block_start_read(g_log.block_being_read, bytes_available);
       if (record != NULL) {
         gpr_mu_unlock(&g_log.lock);
         return record;

src/core/statistics/census_log.h

@@ -40,9 +40,11 @@
 #define CENSUS_LOG_2_MAX_RECORD_SIZE 14 /* 2^14 = 16KB */
 #define CENSUS_LOG_MAX_RECORD_SIZE (1 << CENSUS_LOG_2_MAX_RECORD_SIZE)
 
-/* Initialize the statistics logging subsystem with the given log size. If
-   discard_old_records is non-zero, then new records will displace older
-   ones when the log is full. This function must be called before any other
+/* Initialize the statistics logging subsystem with the given log size. A log
+   size of 0 will result in the smallest possible log for the platform
+   (approximately CENSUS_LOG_MAX_RECORD_SIZE * gpr_cpu_num_cores()). If
+   discard_old_records is non-zero, then new records will displace older ones
+   when the log is full. This function must be called before any other
    census_log functions.
 */
 void census_log_initialize(size_t size_in_mb, int discard_old_records);

test/core/statistics/census_log_tests.c

@@ -41,6 +41,7 @@
 #include <grpc/support/sync.h>
 #include <grpc/support/thd.h>
 #include <grpc/support/time.h>
+#include <grpc/support/useful.h>
 
 /* Fills in 'record' of size 'size'. Each byte in record is filled in with the
    same value. The value is extracted from 'record' pointer. */
@@ -120,12 +121,18 @@ static void assert_log_empty() {
 }
 
 /* Given log size and record size, computes the minimum usable space. */
-static size_t min_usable_space(size_t log_size, size_t record_size) {
+static gpr_int32 min_usable_space(size_t log_size, size_t record_size) {
+  gpr_int32 usable_space;
   gpr_int32 num_blocks = log_size / CENSUS_LOG_MAX_RECORD_SIZE;
   gpr_int32 waste_per_block = CENSUS_LOG_MAX_RECORD_SIZE % record_size;
-  /* In the worst case, all except one core-local block is empty. */
-  return (log_size - ((gpr_cpu_num_cores() - 1) * CENSUS_LOG_MAX_RECORD_SIZE) -
-          ((num_blocks - gpr_cpu_num_cores() - 1) * waste_per_block));
+  /* In the worst case, all except one core-local block is full. */
+  gpr_int32 num_full_blocks = GPR_MAX(gpr_cpu_num_cores() - 2, 2);
+  GPR_ASSERT(num_blocks >= num_full_blocks);
+  usable_space = (gpr_int32)log_size -
+                 (num_full_blocks * CENSUS_LOG_MAX_RECORD_SIZE) -
+                 ((num_blocks - num_full_blocks) * waste_per_block);
+  GPR_ASSERT(usable_space > 0);
+  return usable_space;
 }
 
 /* Fills the log and verifies data. If 'no fragmentation' is true, records
@@ -152,7 +159,6 @@ static void fill_log(size_t log_size, int no_fragmentation, int circular_log) {
   records_written = write_records_to_log(
       0 /* writer id */, size, (log_size / size) * 2, 0 /* spin count */);
   usable_space = min_usable_space(log_size, size);
-  GPR_ASSERT(usable_space > 0);
   GPR_ASSERT(records_written * size >= usable_space);
   records_read = perform_read_iteration(size);
   if (!circular_log) {
@@ -538,6 +544,21 @@ void test_multiple_writers() {
   census_log_shutdown();
 }
 
+/* Repeat the straddling records and multiple writers tests with a small log. */
+void test_small_log() {
+  size_t log_size;
+  const int circular = 0;
+  printf("Starting test: small log\n");
+  census_log_initialize(0, circular);
+  log_size = census_log_remaining_space();
+  GPR_ASSERT(log_size > 0);
+  fill_log(log_size, 0, circular);
+  census_log_shutdown();
+  census_log_initialize(0, circular);
+  multiple_writers_single_reader(circular);
+  census_log_shutdown();
+}
+
 void test_performance() {
   int write_size = 1;
   for (; write_size < CENSUS_LOG_MAX_RECORD_SIZE; write_size *= 2) {

test/core/statistics/census_log_tests.h

@@ -46,5 +46,6 @@ void test_fill_circular_log_with_straddling_records();
 void test_multiple_writers_circular_log();
 void test_multiple_writers();
 void test_performance();
+void test_small_log();
 
 #endif /* __GRPC_TEST_STATISTICS_LOG_TESTS_H__ */

test/core/statistics/small_log_test.c

@@ -0,0 +1,46 @@
+/*
+ *
+ * Copyright 2014, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#include "test/core/statistics/census_log_tests.h"
+
+#include <stdlib.h>
+
+#include <grpc/support/time.h>
+#include "test/core/util/test_config.h"
+
+int main(int argc, char **argv) {
+  grpc_test_init(argc, argv);
+  srand(gpr_now().tv_nsec);
+  test_small_log();
+  return 0;
+}