Initial checkin of gRPC to third_party/

third_party/grpc/src/core/statistics/census_log.c

Index: third_party/grpc/src/core/statistics/census_log.c
diff --git a/third_party/grpc/src/core/statistics/census_log.c b/third_party/grpc/src/core/statistics/census_log.c
new file mode 100644
index 0000000000000000000000000000000000000000..257ba586a32d5fe10f4a0ed1f161fea990d5a0c7
--- /dev/null
+++ b/third_party/grpc/src/core/statistics/census_log.c
@@ -0,0 +1,603 @@
+/*
+ *
+ * Copyright 2015, 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.
+ *
+ */
+
+/* Available log space is divided up in blocks of
+   CENSUS_LOG_2_MAX_RECORD_SIZE bytes. A block can be in one of the
+   following three data structures:
+   - Free blocks (free_block_list)
+   - Blocks with unread data (dirty_block_list)
+   - Blocks currently attached to cores (core_local_blocks[])
+
+   census_log_start_write() moves a block from core_local_blocks[] to the
+   end of dirty_block_list when block:
+   - is out-of-space OR
+   - has an incomplete record (an incomplete record occurs when a thread calls
+     census_log_start_write() and is context-switched before calling
+     census_log_end_write()
+   So, blocks in dirty_block_list are ordered, from oldest to newest, by time
+   when block is detached from the core.
+
+   census_log_read_next() first iterates over dirty_block_list and then
+   core_local_blocks[]. It moves completely read blocks from dirty_block_list
+   to free_block_list. Blocks in core_local_blocks[] are not freed, even when
+   completely read.
+
+   If log is configured to discard old records and free_block_list is empty,
+   census_log_start_write() iterates over dirty_block_list to allocate a
+   new block. It moves the oldest available block (no pending read/write) to
+   core_local_blocks[].
+
+   core_local_block_struct is used to implement a map from core id to the block
+   associated with that core. This mapping is advisory. It is possible that the
+   block returned by this mapping is no longer associated with that core. This
+   mapping is updated, lazily, by census_log_start_write().
+
+   Locking in block struct:
+
+   Exclusive g_log.lock must be held before calling any functions operatong on
+   block structs except census_log_start_write() and
+   census_log_end_write().
+
+   Writes to a block are serialized via writer_lock.
+   census_log_start_write() acquires this lock and
+   census_log_end_write() releases it. On failure to acquire the lock,
+   writer allocates a new block for the current core and updates
+   core_local_block accordingly.
+
+   Simultaneous read and write access is allowed. Reader can safely read up to
+   committed bytes (bytes_committed).
+
+   reader_lock protects the block, currently being read, from getting recycled.
+   start_read() acquires reader_lock and end_read() releases the lock.
+
+   Read/write access to a block is disabled via try_disable_access(). It returns
+   with both writer_lock and reader_lock held. These locks are subsequently
+   released by enable_access() to enable access to the block.
+
+   A note on naming: Most function/struct names are prepended by cl_
+   (shorthand for census_log). Further, functions that manipulate structures
+   include the name of the structure, which will be passed as the first
+   argument. E.g. cl_block_initialize() will initialize a cl_block.
+*/
+#include "src/core/statistics/census_log.h"
+#include <string.h>
+#include <grpc/support/alloc.h>
+#include <grpc/support/atm.h>
+#include <grpc/support/cpu.h>
+#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 */
+
+typedef struct census_log_block_list_struct {
+  struct census_log_block_list_struct *next;
+  struct census_log_block_list_struct *prev;
+  struct census_log_block *block;
+} cl_block_list_struct;
+
+typedef struct census_log_block {
+  /* Pointer to underlying buffer */
+  char *buffer;
+  gpr_atm writer_lock;
+  gpr_atm reader_lock;
+  /* Keeps completely written bytes. Declared atomic because accessed
+     simultaneously by reader and writer. */
+  gpr_atm bytes_committed;
+  /* Bytes already read */
+  int32_t bytes_read;
+  /* Links for list */
+  cl_block_list_struct link;
+/* 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
+   3x gpr_atm             12          24
+   int32_t               4           8 (assumes padding)
+   cl_block_list_struct   12          24
+   TOTAL                  32          64
+
+   Depending on the size of our cacheline and the architecture, we
+   selectively add char buffering to this structure. The size is checked
+   via assert in census_log_initialize(). */
+#if defined(GPR_ARCH_64)
+#define CL_BLOCK_PAD_SIZE (GPR_CACHELINE_SIZE - 64)
+#else
+#if defined(GPR_ARCH_32)
+#define CL_BLOCK_PAD_SIZE (GPR_CACHELINE_SIZE - 32)
+#else
+#error "Unknown architecture"
+#endif
+#endif
+#if CL_BLOCK_PAD_SIZE > 0
+  char padding[CL_BLOCK_PAD_SIZE];
+#endif
+} cl_block;
+
+/* A list of cl_blocks, doubly-linked through cl_block::link. */
+typedef struct census_log_block_list {
+  int32_t count;           /* Number of items in list. */
+  cl_block_list_struct ht; /* head/tail of linked list. */
+} cl_block_list;
+
+/* Cacheline aligned block pointers to avoid false sharing. Block pointer must
+   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 */
+#if defined(GPR_ARCH_64)
+#define CL_CORE_LOCAL_BLOCK_PAD_SIZE (GPR_CACHELINE_SIZE - 8)
+#else
+#if defined(GPR_ARCH_32)
+#define CL_CORE_LOCAL_BLOCK_PAD_SIZE (GPR_CACHELINE_SIZE - 4)
+#else
+#error "Unknown architecture"
+#endif
+#endif
+#if CL_CORE_LOCAL_BLOCK_PAD_SIZE > 0
+  char padding[CL_CORE_LOCAL_BLOCK_PAD_SIZE];
+#endif
+} cl_core_local_block;
+
+struct census_log {
+  int discard_old_records;
+  /* Number of cores (aka hardware-contexts) */
+  unsigned num_cores;
+  /* number of CENSUS_LOG_2_MAX_RECORD_SIZE blocks in log */
+  int32_t num_blocks;
+  cl_block *blocks;                       /* Block metadata. */
+  cl_core_local_block *core_local_blocks; /* Keeps core to block mappings. */
+  gpr_mu lock;
+  int initialized; /* has log been initialized? */
+  /* Keeps the state of the reader iterator. A value of 0 indicates that
+     iterator has reached the end. census_log_init_reader() resets the
+     value to num_core to restart iteration. */
+  uint32_t read_iterator_state;
+  /* Points to the block being read. If non-NULL, the block is locked for
+     reading (block_being_read_->reader_lock is held). */
+  cl_block *block_being_read;
+  /* A non-zero value indicates that log is full. */
+  gpr_atm is_full;
+  char *buffer;
+  cl_block_list free_block_list;
+  cl_block_list dirty_block_list;
+  gpr_atm out_of_space_count;
+};
+
+/* Single internal log */
+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); }
+
+/* Functions that operate on cl_core_local_block's */
+
+static void cl_core_local_block_set_block(cl_core_local_block *clb,
+                                          cl_block *block) {
+  gpr_atm_rel_store(&clb->block, (gpr_atm)block);
+}
+
+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,
+                                            cl_block *block) {
+  bls->next = bls->prev = bls;
+  bls->block = block;
+}
+
+/* Functions that operate on cl_block_list's */
+
+static void cl_block_list_initialize(cl_block_list *list) {
+  list->count = 0;
+  cl_block_list_struct_initialize(&list->ht, NULL);
+}
+
+/* Returns head of *this, or NULL if empty. */
+static cl_block *cl_block_list_head(cl_block_list *list) {
+  return list->ht.next->block;
+}
+
+/* Insert element *e after *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;
+  e->prev = pos;
+  e->next->prev = e;
+  e->prev->next = e;
+}
+
+/* Insert block at the head of the list */
+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) {
+  cl_block_list_insert(list, list->ht.prev, &block->link);
+}
+
+/* Removes block *b. Requires *b be in the list. */
+static void cl_block_list_remove(cl_block_list *list, cl_block *b) {
+  list->count--;
+  b->link.next->prev = b->link.prev;
+  b->link.prev->next = b->link.next;
+}
+
+/* Functions that operate on cl_block's */
+
+static void cl_block_initialize(cl_block *block, char *buffer) {
+  block->buffer = buffer;
+  gpr_atm_rel_store(&block->writer_lock, 0);
+  gpr_atm_rel_store(&block->reader_lock, 0);
+  gpr_atm_rel_store(&block->bytes_committed, 0);
+  block->bytes_read = 0;
+  cl_block_list_struct_initialize(&block->link, block);
+}
+
+/* Guards against exposing partially written buffer to the reader. */
+static void cl_block_set_bytes_committed(cl_block *block,
+                                         int32_t bytes_committed) {
+  gpr_atm_rel_store(&block->bytes_committed, bytes_committed);
+}
+
+static int32_t cl_block_get_bytes_committed(cl_block *block) {
+  return gpr_atm_acq_load(&block->bytes_committed);
+}
+
+/* Tries to disable future read/write access to this block. Succeeds if:
+   - no in-progress write AND
+   - no in-progress read AND
+   - 'discard_data' set to true OR no unread data
+   On success, clears the block state and returns with writer_lock_ and
+   reader_lock_ held. These locks are released by a subsequent
+   cl_block_access_enable() call. */
+static int cl_block_try_disable_access(cl_block *block, int discard_data) {
+  if (!cl_try_lock(&block->writer_lock)) {
+    return 0;
+  }
+  if (!cl_try_lock(&block->reader_lock)) {
+    cl_unlock(&block->writer_lock);
+    return 0;
+  }
+  if (!discard_data &&
+      (block->bytes_read != cl_block_get_bytes_committed(block))) {
+    cl_unlock(&block->reader_lock);
+    cl_unlock(&block->writer_lock);
+    return 0;
+  }
+  cl_block_set_bytes_committed(block, 0);
+  block->bytes_read = 0;
+  return 1;
+}
+
+static void cl_block_enable_access(cl_block *block) {
+  cl_unlock(&block->reader_lock);
+  cl_unlock(&block->writer_lock);
+}
+
+/* Returns with writer_lock held. */
+static void *cl_block_start_write(cl_block *block, size_t size) {
+  int32_t bytes_committed;
+  if (!cl_try_lock(&block->writer_lock)) {
+    return NULL;
+  }
+  bytes_committed = cl_block_get_bytes_committed(block);
+  if (bytes_committed + size > CENSUS_LOG_MAX_RECORD_SIZE) {
+    cl_unlock(&block->writer_lock);
+    return NULL;
+  }
+  return block->buffer + bytes_committed;
+}
+
+/* Releases writer_lock and increments committed bytes by 'bytes_written'.
+  'bytes_written' must be <= 'size' specified in the corresponding
+  StartWrite() call. This function is thread-safe. */
+static void cl_block_end_write(cl_block *block, size_t bytes_written) {
+  cl_block_set_bytes_committed(
+      block, cl_block_get_bytes_committed(block) + bytes_written);
+  cl_unlock(&block->writer_lock);
+}
+
+/* Returns a pointer to the first unread byte in buffer. The number of bytes
+   available are returned in 'bytes_available'. Acquires reader lock that is
+   released by a subsequent cl_block_end_read() call. Returns NULL if:
+   - read in progress
+   - no data available */
+static void *cl_block_start_read(cl_block *block, size_t *bytes_available) {
+  void *record;
+  if (!cl_try_lock(&block->reader_lock)) {
+    return NULL;
+  }
+  /* bytes_committed may change from under us. Use bytes_available to update
+     bytes_read below. */
+  *bytes_available = cl_block_get_bytes_committed(block) - block->bytes_read;
+  if (*bytes_available == 0) {
+    cl_unlock(&block->reader_lock);
+    return NULL;
+  }
+  record = block->buffer + block->bytes_read;
+  block->bytes_read += *bytes_available;
+  return record;
+}
+
+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
+   configured to discard old records). Returns NULL if out-of-space. */
+static cl_block *cl_allocate_block(void) {
+  cl_block *block = cl_block_list_head(&g_log.free_block_list);
+  if (block != NULL) {
+    cl_block_list_remove(&g_log.free_block_list, block);
+    return block;
+  }
+  if (!g_log.discard_old_records) {
+    /* No free block and log is configured to keep old records. */
+    return NULL;
+  }
+  /* Recycle dirty block. Start from the oldest. */
+  for (block = cl_block_list_head(&g_log.dirty_block_list); block != NULL;
+       block = block->link.next->block) {
+    if (cl_block_try_disable_access(block, 1 /* discard data */)) {
+      cl_block_list_remove(&g_log.dirty_block_list, block);
+      return block;
+    }
+  }
+  return NULL;
+}
+
+/* Allocates a new block and updates core id => block mapping. 'old_block'
+   points to the block that the caller thinks is attached to
+   'core_id'. 'old_block' may be NULL. Returns non-zero if:
+   - allocated a new block OR
+   - 'core_id' => 'old_block' mapping changed (another thread allocated a
+     block before lock was acquired). */
+static int cl_allocate_core_local_block(int32_t core_id, cl_block *old_block) {
+  /* Now that we have the lock, check if core-local mapping has changed. */
+  cl_core_local_block *core_local_block = &g_log.core_local_blocks[core_id];
+  cl_block *block = cl_core_local_block_get_block(core_local_block);
+  if ((block != NULL) && (block != old_block)) {
+    return 1;
+  }
+  if (block != NULL) {
+    cl_core_local_block_set_block(core_local_block, NULL);
+    cl_block_list_insert_at_tail(&g_log.dirty_block_list, block);
+  }
+  block = cl_allocate_block();
+  if (block == NULL) {
+    gpr_atm_rel_store(&g_log.is_full, 1);
+    return 0;
+  }
+  cl_core_local_block_set_block(core_local_block, block);
+  cl_block_enable_access(block);
+  return 1;
+}
+
+static cl_block *cl_get_block(void *record) {
+  uintptr_t p = (uintptr_t)((char *)record - g_log.buffer);
+  uintptr_t index = p >> CENSUS_LOG_2_MAX_RECORD_SIZE;
+  return &g_log.blocks[index];
+}
+
+/* Gets the next block to read and tries to free 'prev' block (if not NULL).
+   Returns NULL if reached the end. */
+static cl_block *cl_next_block_to_read(cl_block *prev) {
+  cl_block *block = NULL;
+  if (g_log.read_iterator_state == g_log.num_cores) {
+    /* We are traversing dirty list; find the next dirty block. */
+    if (prev != NULL) {
+      /* Try to free the previous block if there is no unread data. This block
+         may have unread data if previously incomplete record completed between
+         read_next() calls. */
+      block = prev->link.next->block;
+      if (cl_block_try_disable_access(prev, 0 /* do not discard data */)) {
+        cl_block_list_remove(&g_log.dirty_block_list, prev);
+        cl_block_list_insert_at_head(&g_log.free_block_list, prev);
+        gpr_atm_rel_store(&g_log.is_full, 0);
+      }
+    } else {
+      block = cl_block_list_head(&g_log.dirty_block_list);
+    }
+    if (block != NULL) {
+      return block;
+    }
+    /* We are done with the dirty list; moving on to core-local blocks. */
+  }
+  while (g_log.read_iterator_state > 0) {
+    g_log.read_iterator_state--;
+    block = cl_core_local_block_get_block(
+        &g_log.core_local_blocks[g_log.read_iterator_state]);
+    if (block != NULL) {
+      return block;
+    }
+  }
+  return NULL;
+}
+
+/* External functions: primary stats_log interface */
+void census_log_initialize(size_t size_in_mb, int discard_old_records) {
+  int32_t ix;
+  /* 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();
+  /* 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;
+  gpr_atm_rel_store(&g_log.is_full, 0);
+  g_log.core_local_blocks = (cl_core_local_block *)gpr_malloc_aligned(
+      g_log.num_cores * sizeof(cl_core_local_block), GPR_CACHELINE_SIZE_LOG);
+  memset(g_log.core_local_blocks, 0,
+         g_log.num_cores * sizeof(cl_core_local_block));
+  g_log.blocks = (cl_block *)gpr_malloc_aligned(
+      g_log.num_blocks * sizeof(cl_block), GPR_CACHELINE_SIZE_LOG);
+  memset(g_log.blocks, 0, g_log.num_blocks * sizeof(cl_block));
+  g_log.buffer = gpr_malloc(g_log.num_blocks * CENSUS_LOG_MAX_RECORD_SIZE);
+  memset(g_log.buffer, 0, g_log.num_blocks * CENSUS_LOG_MAX_RECORD_SIZE);
+  cl_block_list_initialize(&g_log.free_block_list);
+  cl_block_list_initialize(&g_log.dirty_block_list);
+  for (ix = 0; ix < g_log.num_blocks; ++ix) {
+    cl_block *block = g_log.blocks + ix;
+    cl_block_initialize(block,
+                        g_log.buffer + (CENSUS_LOG_MAX_RECORD_SIZE * ix));
+    cl_block_try_disable_access(block, 1 /* discard data */);
+    cl_block_list_insert_at_tail(&g_log.free_block_list, block);
+  }
+  gpr_atm_rel_store(&g_log.out_of_space_count, 0);
+  g_log.initialized = 1;
+}
+
+void census_log_shutdown(void) {
+  GPR_ASSERT(g_log.initialized);
+  gpr_mu_destroy(&g_log.lock);
+  gpr_free_aligned(g_log.core_local_blocks);
+  g_log.core_local_blocks = NULL;
+  gpr_free_aligned(g_log.blocks);
+  g_log.blocks = NULL;
+  gpr_free(g_log.buffer);
+  g_log.buffer = NULL;
+  g_log.initialized = 0;
+}
+
+void *census_log_start_write(size_t size) {
+  /* Used to bound number of times block allocation is attempted. */
+  int32_t attempts_remaining = g_log.num_blocks;
+  /* TODO(aveitch): move this inside the do loop when current_cpu is fixed */
+  int32_t core_id = gpr_cpu_current_cpu();
+  GPR_ASSERT(g_log.initialized);
+  if (size > CENSUS_LOG_MAX_RECORD_SIZE) {
+    return NULL;
+  }
+  do {
+    int allocated;
+    void *record = NULL;
+    cl_block *block =
+        cl_core_local_block_get_block(&g_log.core_local_blocks[core_id]);
+    if (block && (record = cl_block_start_write(block, size))) {
+      return record;
+    }
+    /* Need to allocate a new block. We are here if:
+       - No block associated with the core OR
+       - Write in-progress on the block OR
+       - block is out of space */
+    if (gpr_atm_acq_load(&g_log.is_full)) {
+      gpr_atm_no_barrier_fetch_add(&g_log.out_of_space_count, 1);
+      return NULL;
+    }
+    gpr_mu_lock(&g_log.lock);
+    allocated = cl_allocate_core_local_block(core_id, block);
+    gpr_mu_unlock(&g_log.lock);
+    if (!allocated) {
+      gpr_atm_no_barrier_fetch_add(&g_log.out_of_space_count, 1);
+      return NULL;
+    }
+  } while (attempts_remaining--);
+  /* Give up. */
+  gpr_atm_no_barrier_fetch_add(&g_log.out_of_space_count, 1);
+  return NULL;
+}
+
+void census_log_end_write(void *record, size_t bytes_written) {
+  GPR_ASSERT(g_log.initialized);
+  cl_block_end_write(cl_get_block(record), bytes_written);
+}
+
+void census_log_init_reader(void) {
+  GPR_ASSERT(g_log.initialized);
+  gpr_mu_lock(&g_log.lock);
+  /* If a block is locked for reading unlock it. */
+  if (g_log.block_being_read != NULL) {
+    cl_block_end_read(g_log.block_being_read);
+    g_log.block_being_read = NULL;
+  }
+  g_log.read_iterator_state = g_log.num_cores;
+  gpr_mu_unlock(&g_log.lock);
+}
+
+const void *census_log_read_next(size_t *bytes_available) {
+  GPR_ASSERT(g_log.initialized);
+  gpr_mu_lock(&g_log.lock);
+  if (g_log.block_being_read != NULL) {
+    cl_block_end_read(g_log.block_being_read);
+  }
+  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);
+      if (record != NULL) {
+        gpr_mu_unlock(&g_log.lock);
+        return record;
+      }
+    }
+  } while (g_log.block_being_read != NULL);
+  gpr_mu_unlock(&g_log.lock);
+  return NULL;
+}
+
+size_t census_log_remaining_space(void) {
+  size_t space;
+  GPR_ASSERT(g_log.initialized);
+  gpr_mu_lock(&g_log.lock);
+  if (g_log.discard_old_records) {
+    /* Remaining space is not meaningful; just return the entire log space. */
+    space = g_log.num_blocks << CENSUS_LOG_2_MAX_RECORD_SIZE;
+  } else {
+    space = g_log.free_block_list.count * CENSUS_LOG_MAX_RECORD_SIZE;
+  }
+  gpr_mu_unlock(&g_log.lock);
+  return space;
+}
+
+int census_log_out_of_space_count(void) {
+  GPR_ASSERT(g_log.initialized);
+  return gpr_atm_acq_load(&g_log.out_of_space_count);
+}