initial commit
diff --git a/src/core/census/log.c b/src/core/census/log.c
new file mode 100644
index 0000000..a76f510
--- /dev/null
+++ b/src/core/census/log.c
@@ -0,0 +1,610 @@
+/*
+ *
+ * Copyright 2015-2016, 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. Readers 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/census/log.h"
+#include <grpc/support/alloc.h>
+#include <grpc/support/atm.h>
+#include <grpc/support/cpu.h>
+#include <grpc/support/log.h>
+#include <grpc/support/sync.h>
+#include <grpc/support/useful.h>
+#include <stdbool.h>
+#include <string.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 */
+ size_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
+ size_t 4 8
+ 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 */
+ uint32_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,
+ size_t bytes_committed) {
+ gpr_atm_rel_store(&block->bytes_committed, (gpr_atm)bytes_committed);
+}
+
+static size_t cl_block_get_bytes_committed(cl_block* block) {
+ return (size_t)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 bool cl_block_try_disable_access(cl_block* block, int discard_data) {
+ if (!cl_try_lock(&block->writer_lock)) {
+ return false;
+ }
+ if (!cl_try_lock(&block->reader_lock)) {
+ cl_unlock(&block->writer_lock);
+ return false;
+ }
+ if (!discard_data &&
+ (block->bytes_read != cl_block_get_bytes_committed(block))) {
+ cl_unlock(&block->reader_lock);
+ cl_unlock(&block->writer_lock);
+ return false;
+ }
+ cl_block_set_bytes_committed(block, 0);
+ block->bytes_read = 0;
+ return true;
+}
+
+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) {
+ size_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) {
+ if (!cl_try_lock(&block->reader_lock)) {
+ return NULL;
+ }
+ /* bytes_committed may change from under us. Use bytes_available to update
+ bytes_read below. */
+ size_t bytes_committed = cl_block_get_bytes_committed(block);
+ GPR_ASSERT(bytes_committed >= block->bytes_read);
+ *bytes_available = bytes_committed - block->bytes_read;
+ if (*bytes_available == 0) {
+ cl_unlock(&block->reader_lock);
+ return NULL;
+ }
+ void* 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 true if:
+ - allocated a new block OR
+ - 'core_id' => 'old_block' mapping changed (another thread allocated a
+ block before lock was acquired). */
+static bool cl_allocate_core_local_block(uint32_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 true;
+ }
+ 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 false;
+ }
+ cl_core_local_block_set_block(core_local_block, block);
+ cl_block_enable_access(block);
+ return true;
+}
+
+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;
+}
+
+#define CL_LOG_2_MB 20 /* 2^20 = 1MB */
+
+/* External functions: primary stats_log interface */
+void census_log_initialize(size_t size_in_mb, int discard_old_records) {
+ /* 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 that we will not get any overflow in calaculating num_blocks */
+ GPR_ASSERT(CL_LOG_2_MB >= CENSUS_LOG_2_MAX_RECORD_SIZE);
+ GPR_ASSERT(size_in_mb < 1000);
+ /* Ensure at least as many blocks as there are cores. */
+ g_log.num_blocks =
+ (uint32_t)GPR_MAX(g_log.num_cores, (size_in_mb << CL_LOG_2_MB) >>
+ 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 (uint32_t i = 0; i < g_log.num_blocks; ++i) {
+ cl_block* block = g_log.blocks + i;
+ cl_block_initialize(block, g_log.buffer + (CENSUS_LOG_MAX_RECORD_SIZE * i));
+ 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. */
+ GPR_ASSERT(size > 0);
+ GPR_ASSERT(g_log.initialized);
+ if (size > CENSUS_LOG_MAX_RECORD_SIZE) {
+ return NULL;
+ }
+ uint32_t attempts_remaining = g_log.num_blocks;
+ uint32_t core_id = gpr_cpu_current_cpu();
+ do {
+ 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);
+ bool 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) {
+ GPR_ASSERT(g_log.initialized);
+ size_t space = 0;
+ 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 {
+ GPR_ASSERT(g_log.free_block_list.count >= 0);
+ space = (size_t)g_log.free_block_list.count * CENSUS_LOG_MAX_RECORD_SIZE;
+ }
+ gpr_mu_unlock(&g_log.lock);
+ return space;
+}
+
+int64_t census_log_out_of_space_count(void) {
+ GPR_ASSERT(g_log.initialized);
+ return gpr_atm_acq_load(&g_log.out_of_space_count);
+}
diff --git a/src/core/census/log.h b/src/core/census/log.h
new file mode 100644
index 0000000..05daea0
--- /dev/null
+++ b/src/core/census/log.h
@@ -0,0 +1,93 @@
+/*
+ *
+ * Copyright 2015-2016, 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.
+ *
+ */
+
+#ifndef GRPC_INTERNAL_CORE_CENSUS_LOG_H
+#define GRPC_INTERNAL_CORE_CENSUS_LOG_H
+
+#include <grpc/support/port_platform.h>
+#include <stddef.h>
+
+/* Maximum record size, in bytes. */
+#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. 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);
+
+/* Shutdown the logging subsystem. Caller must ensure that:
+ - no in progress or future call to any census_log functions
+ - no incomplete records
+*/
+void census_log_shutdown(void);
+
+/* Allocates and returns a 'size' bytes record and marks it in use. A
+ subsequent census_log_end_write() marks the record complete. The
+ 'bytes_written' census_log_end_write() argument must be <=
+ 'size'. Returns NULL if out-of-space AND:
+ - log is configured to keep old records OR
+ - all blocks are pinned by incomplete records.
+*/
+void* census_log_start_write(size_t size);
+
+void census_log_end_write(void* record, size_t bytes_written);
+
+void census_log_init_reader(void);
+
+/* census_log_read_next() iterates over blocks with data and for each block
+ returns a pointer to the first unread byte. The number of bytes that can be
+ read are returned in 'bytes_available'. Reader is expected to read all
+ available data. Reading the data consumes it i.e. it cannot be read again.
+ census_log_read_next() returns NULL if the end is reached i.e last block
+ is read. census_log_init_reader() starts the iteration or aborts the
+ current iteration.
+*/
+const void* census_log_read_next(size_t* bytes_available);
+
+/* Returns estimated remaining space across all blocks, in bytes. If log is
+ configured to discard old records, returns total log space. Otherwise,
+ returns space available in empty blocks (partially filled blocks are
+ treated as full).
+*/
+size_t census_log_remaining_space(void);
+
+/* Returns the number of times gprc_stats_log_start_write() failed due to
+ out-of-space. */
+int64_t census_log_out_of_space_count(void);
+
+#endif /* GRPC_INTERNAL_CORE_CENSUS_LOG_H */
diff --git a/src/python/grpcio/grpc_core_dependencies.py b/src/python/grpcio/grpc_core_dependencies.py
index 708091d..ea63b41 100644
--- a/src/python/grpcio/grpc_core_dependencies.py
+++ b/src/python/grpcio/grpc_core_dependencies.py
@@ -222,6 +222,7 @@
'src/core/transport/transport_op_string.c',
'src/core/census/context.c',
'src/core/census/initialize.c',
+ 'src/core/census/log.c',
'src/core/census/operation.c',
'src/core/census/placeholders.c',
'src/core/census/tag_set.c',