Enabled background and reply time tracking on blocked on keys/blocked on background work clients (#7491)

This commit enables tracking time of the background tasks and on replies,
opening the door for properly tracking commands that rely on blocking / background
 work via the slowlog, latency history, and commandstats. 

Some notes:
- The time spent blocked waiting for key changes, or blocked on synchronous
  replication is not accounted for. 

- **This commit does not affect latency tracking of commands that are non-blocking
  or do not have background work.** ( meaning that it all stays the same with exception to
  `BZPOPMIN`,`BZPOPMAX`,`BRPOP`,`BLPOP`, etc... and module's commands that rely
  on background threads ). 

-  Specifically for latency history command we've added a new event class named
  `command-unblocking` that will enable latency monitoring on commands that spawn
  background threads to do the work.

- For blocking commands we're now considering the total time of a command as the
  time spent on call() + the time spent on replying when unblocked.

- For Modules commands that rely on background threads we're now considering the
  total time of a command as the time spent on call (main thread) + the time spent on
  the background thread ( if marked within `RedisModule_MeasureTimeStart()` and
  `RedisModule_MeasureTimeEnd()` ) + the time spent on replying (main thread)

To test for this feature we've added a `unit/moduleapi/blockonbackground` test that relies on
a module that blocks the client and sleeps on the background for a given time. 
- check blocked command that uses RedisModule_MeasureTimeStart() is tracking background time
- check blocked command that uses RedisModule_MeasureTimeStart() is tracking background time even in timeout
- check blocked command with multiple calls RedisModule_MeasureTimeStart()  is tracking the total background time
- check blocked command without calling RedisModule_MeasureTimeStart() is not reporting background time

runtest-moduleapi

@@ -23,6 +23,7 @@ $TCLSH tests/test_helper.tcl \
 --single unit/moduleapi/hooks \
 --single unit/moduleapi/misc \
 --single unit/moduleapi/blockonkeys \
+--single unit/moduleapi/blockonbackground \
 --single unit/moduleapi/scan \
 --single unit/moduleapi/datatype \
 --single unit/moduleapi/auth \

src/blocked.c

@@ -61,6 +61,9 @@
  */
 
 #include "server.h"
+#include "slowlog.h"
+#include "latency.h"
+#include "monotonic.h"
 
 int serveClientBlockedOnList(client *receiver, robj *key, robj *dstkey, redisDb *db, robj *value, int wherefrom, int whereto);
 int getListPositionFromObjectOrReply(client *c, robj *arg, int *position);
@@ -97,6 +100,20 @@ void blockClient(client *c, int btype) {
     }
 }
 
+/* This function is called after a client has finished a blocking operation
+ * in order to update the total command duration, log the command into
+ * the Slow log if needed, and log the reply duration event if needed. */
+void updateStatsOnUnblock(client *c, long blocked_us, long reply_us){
+    const ustime_t total_cmd_duration = c->duration + blocked_us + reply_us;
+    c->lastcmd->microseconds += total_cmd_duration;
+    /* Log the command into the Slow log if needed. */
+    if (!(c->lastcmd->flags & CMD_SKIP_SLOWLOG)) {
+        slowlogPushEntryIfNeeded(c,c->argv,c->argc,total_cmd_duration);
+        /* Log the reply duration event. */
+        latencyAddSampleIfNeeded("command-unblocking",reply_us/1000);
+    }
+}
+
 /* This function is called in the beforeSleep() function of the event loop
  * in order to process the pending input buffer of clients that were
  * unblocked after a blocking operation. */
@@ -264,6 +281,8 @@ void serveClientsBlockedOnListKey(robj *o, readyList *rl) {
                 if (dstkey) incrRefCount(dstkey);
                 unblockClient(receiver);
 
+                monotime replyTimer;
+                elapsedStart(&replyTimer);
                 if (serveClientBlockedOnList(receiver,
                     rl->key,dstkey,rl->db,value,
                     wherefrom, whereto) == C_ERR)
@@ -272,6 +291,7 @@ void serveClientsBlockedOnListKey(robj *o, readyList *rl) {
                      * to also undo the POP operation. */
                     listTypePush(o,value,wherefrom);
                 }
+                updateStatsOnUnblock(receiver, 0, elapsedUs(replyTimer));
 
                 if (dstkey) decrRefCount(dstkey);
                 decrRefCount(value);
@@ -316,7 +336,10 @@ void serveClientsBlockedOnSortedSetKey(robj *o, readyList *rl) {
                          receiver->lastcmd->proc == bzpopminCommand)
                          ? ZSET_MIN : ZSET_MAX;
             unblockClient(receiver);
+            monotime replyTimer;
+            elapsedStart(&replyTimer);
             genericZpopCommand(receiver,&rl->key,1,where,1,NULL);
+            updateStatsOnUnblock(receiver, 0, elapsedUs(replyTimer));
             zcard--;
 
             /* Replicate the command. */
@@ -406,6 +429,8 @@ void serveClientsBlockedOnStreamKey(robj *o, readyList *rl) {
                     }
                 }
 
+                monotime replyTimer;
+                elapsedStart(&replyTimer);
                 /* Emit the two elements sub-array consisting of
                  * the name of the stream and the data we
                  * extracted from it. Wrapped in a single-item
@@ -425,6 +450,7 @@ void serveClientsBlockedOnStreamKey(robj *o, readyList *rl) {
                 streamReplyWithRange(receiver,s,&start,NULL,
                                      receiver->bpop.xread_count,
                                      0, group, consumer, noack, &pi);
+                updateStatsOnUnblock(receiver, 0, elapsedUs(replyTimer));
 
                 /* Note that after we unblock the client, 'gt'
                  * and other receiver->bpop stuff are no longer
@@ -471,7 +497,10 @@ void serveClientsBlockedOnKeyByModule(readyList *rl) {
              * different modules with different triggers to consider if a key
              * is ready or not. This means we can't exit the loop but need
              * to continue after the first failure. */
+            monotime replyTimer;
+            elapsedStart(&replyTimer);
             if (!moduleTryServeClientBlockedOnKey(receiver, rl->key)) continue;
+            updateStatsOnUnblock(receiver, 0, elapsedUs(replyTimer));
 
             moduleUnblockClient(receiver);
         }

src/module.c

@@ -29,7 +29,9 @@
 
 #include "server.h"
 #include "cluster.h"
+#include "slowlog.h"
 #include "rdb.h"
+#include "monotonic.h"
 #include <dlfcn.h>
 #include <sys/stat.h>
 #include <sys/wait.h>
@@ -262,6 +264,9 @@ typedef struct RedisModuleBlockedClient {
     int dbid;           /* Database number selected by the original client. */
     int blocked_on_keys;    /* If blocked via RM_BlockClientOnKeys(). */
     int unblocked;          /* Already on the moduleUnblocked list. */
+    monotime background_timer; /* Timer tracking the start of background work */
+    uint64_t background_duration; /* Current command background time duration.
+                                     Used for measuring latency of blocking cmds */
 } RedisModuleBlockedClient;
 
 static pthread_mutex_t moduleUnblockedClientsMutex = PTHREAD_MUTEX_INITIALIZER;
@@ -915,6 +920,30 @@ long long RM_Milliseconds(void) {
     return mstime();
 }
 
+/* Mark a point in time that will be used as the start time to calculate
+ * the elapsed execution time when RM_BlockedClientMeasureTimeEnd() is called.
+ * Within the same command, you can call multiple times
+ * RM_BlockedClientMeasureTimeStart() and RM_BlockedClientMeasureTimeEnd()
+ * to accummulate indepedent time intervals to the background duration.
+ * This method always return REDISMODULE_OK. */
+int RM_BlockedClientMeasureTimeStart(RedisModuleBlockedClient *bc) {
+    elapsedStart(&(bc->background_timer));
+    return REDISMODULE_OK;
+}
+
+/* Mark a point in time that will be used as the end time
+ * to calculate the elapsed execution time.
+ * On success REDISMODULE_OK is returned.
+ * This method only returns REDISMODULE_ERR if no start time was
+ * previously defined ( meaning RM_BlockedClientMeasureTimeStart was not called ). */
+int RM_BlockedClientMeasureTimeEnd(RedisModuleBlockedClient *bc) {
+    // If the counter is 0 then we haven't called RM_BlockedClientMeasureTimeStart
+    if (!bc->background_timer)
+        return REDISMODULE_ERR;
+    bc->background_duration += elapsedUs(bc->background_timer);
+    return REDISMODULE_OK;
+}
+
 /* Set flags defining capabilities or behavior bit flags.
  *
  * REDISMODULE_OPTIONS_HANDLE_IO_ERRORS:
@@ -5091,6 +5120,7 @@ RedisModuleBlockedClient *moduleBlockClient(RedisModuleCtx *ctx, RedisModuleCmdF
     bc->dbid = c->db->id;
     bc->blocked_on_keys = keys != NULL;
     bc->unblocked = 0;
+    bc->background_duration = 0;
     c->bpop.timeout = timeout;
 
     if (islua || ismulti) {
@@ -5164,6 +5194,11 @@ int moduleTryServeClientBlockedOnKey(client *c, robj *key) {
  *
  * In these cases, a call to RedisModule_BlockClient() will **not** block the
  * client, but instead produce a specific error reply.
+ *
+ * Measuring background time: By default the time spent in the blocked command
+ * is not account for the total command duration. To include such time you should
+ * use RM_BlockedClientMeasureTimeStart() and RM_BlockedClientMeasureTimeEnd() one,
+ * or multiple times within the blocking command background work.
  */
 RedisModuleBlockedClient *RM_BlockClient(RedisModuleCtx *ctx, RedisModuleCmdFunc reply_callback, RedisModuleCmdFunc timeout_callback, void (*free_privdata)(RedisModuleCtx*,void*), long long timeout_ms) {
     return moduleBlockClient(ctx,reply_callback,timeout_callback,free_privdata,timeout_ms, NULL,0,NULL);
@@ -5358,6 +5393,7 @@ void moduleHandleBlockedClients(void) {
          * was blocked on keys (RM_BlockClientOnKeys()), because we already
          * called such callback in moduleTryServeClientBlockedOnKey() when
          * the key was signaled as ready. */
+        uint64_t reply_us = 0;
         if (c && !bc->blocked_on_keys && bc->reply_callback) {
             RedisModuleCtx ctx = REDISMODULE_CTX_INIT;
             ctx.flags |= REDISMODULE_CTX_BLOCKED_REPLY;
@@ -5366,9 +5402,19 @@ void moduleHandleBlockedClients(void) {
             ctx.module = bc->module;
             ctx.client = bc->client;
             ctx.blocked_client = bc;
+            monotime replyTimer;
+            elapsedStart(&replyTimer);
             bc->reply_callback(&ctx,(void**)c->argv,c->argc);
+            reply_us = elapsedUs(replyTimer);
             moduleFreeContext(&ctx);
         }
+        /* Update stats now that we've finished the blocking operation.
+         * This needs to be out of the reply callback above given that a
+         * module might not define any callback and still do blocking ops.
+         */
+        if (c && !bc->blocked_on_keys) {
+            updateStatsOnUnblock(c, bc->background_duration, reply_us);
+        }
 
         /* Free privdata if any. */
         if (bc->privdata && bc->free_privdata) {
@@ -5432,6 +5478,9 @@ void moduleBlockedClientTimedOut(client *c) {
     ctx.blocked_privdata = bc->privdata;
     bc->timeout_callback(&ctx,(void**)c->argv,c->argc);
     moduleFreeContext(&ctx);
+    if (!bc->blocked_on_keys) {
+        updateStatsOnUnblock(c, bc->background_duration, 0);
+    }
     /* For timeout events, we do not want to call the disconnect callback,
      * because the blocked client will be automatically disconnected in
      * this case, and the user can still hook using the timeout callback. */
@@ -9094,6 +9143,8 @@ void moduleRegisterCoreAPI(void) {
     REGISTER_API(GetBlockedClientPrivateData);
     REGISTER_API(AbortBlock);
     REGISTER_API(Milliseconds);
+    REGISTER_API(BlockedClientMeasureTimeStart);
+    REGISTER_API(BlockedClientMeasureTimeEnd);
     REGISTER_API(GetThreadSafeContext);
     REGISTER_API(GetDetachedThreadSafeContext);
     REGISTER_API(FreeThreadSafeContext);

src/redismodule.h

@@ -776,6 +776,8 @@ REDISMODULE_API int (*RedisModule_IsBlockedTimeoutRequest)(RedisModuleCtx *ctx)
 REDISMODULE_API void * (*RedisModule_GetBlockedClientPrivateData)(RedisModuleCtx *ctx) REDISMODULE_ATTR;
 REDISMODULE_API RedisModuleBlockedClient * (*RedisModule_GetBlockedClientHandle)(RedisModuleCtx *ctx) REDISMODULE_ATTR;
 REDISMODULE_API int (*RedisModule_AbortBlock)(RedisModuleBlockedClient *bc) REDISMODULE_ATTR;
+REDISMODULE_API int (*RedisModule_BlockedClientMeasureTimeStart)(RedisModuleBlockedClient *bc) REDISMODULE_ATTR;
+REDISMODULE_API int (*RedisModule_BlockedClientMeasureTimeEnd)(RedisModuleBlockedClient *bc) REDISMODULE_ATTR;
 REDISMODULE_API RedisModuleCtx * (*RedisModule_GetThreadSafeContext)(RedisModuleBlockedClient *bc) REDISMODULE_ATTR;
 REDISMODULE_API RedisModuleCtx * (*RedisModule_GetDetachedThreadSafeContext)(RedisModuleCtx *ctx) REDISMODULE_ATTR;
 REDISMODULE_API void (*RedisModule_FreeThreadSafeContext)(RedisModuleCtx *ctx) REDISMODULE_ATTR;
@@ -1049,6 +1051,8 @@ static int RedisModule_Init(RedisModuleCtx *ctx, const char *name, int ver, int
     REDISMODULE_GET_API(GetBlockedClientPrivateData);
     REDISMODULE_GET_API(GetBlockedClientHandle);
     REDISMODULE_GET_API(AbortBlock);
+    REDISMODULE_GET_API(BlockedClientMeasureTimeStart);
+    REDISMODULE_GET_API(BlockedClientMeasureTimeEnd);
     REDISMODULE_GET_API(SetDisconnectCallback);
     REDISMODULE_GET_API(SubscribeToKeyspaceEvents);
     REDISMODULE_GET_API(NotifyKeyspaceEvent);

src/server.c

@@ -3620,7 +3620,7 @@ void preventCommandReplication(client *c) {
  */
 void call(client *c, int flags) {
     long long dirty;
-    ustime_t start, duration;
+    monotime call_timer;
     int client_old_flags = c->flags;
     struct redisCommand *real_cmd = c->cmd;
     static long long prev_err_count;
@@ -3646,9 +3646,10 @@ void call(client *c, int flags) {
     dirty = server.dirty;
     prev_err_count = server.stat_total_error_replies;
     updateCachedTime(0);
-    start = server.ustime;
+    elapsedStart(&call_timer);
     c->cmd->proc(c);
-    duration = ustime()-start;
+    const long duration = elapsedUs(call_timer);
+    c->duration = duration;
     dirty = server.dirty-dirty;
     if (dirty < 0) dirty = 0;
 
@@ -3692,7 +3693,10 @@ void call(client *c, int flags) {
          * arguments. */
         robj **argv = c->original_argv ? c->original_argv : c->argv;
         int argc = c->original_argv ? c->original_argc : c->argc;
-        slowlogPushEntryIfNeeded(c,argv,argc,duration);
+        /* If the client is blocked we will handle slowlog when it is unblocked . */
+        if (!(c->flags & CLIENT_BLOCKED)) {
+            slowlogPushEntryIfNeeded(c,argv,argc,duration);
+        }
     }
     freeClientOriginalArgv(c);
 

src/server.h

@@ -881,6 +881,7 @@ typedef struct client {
     size_t sentlen;         /* Amount of bytes already sent in the current
                                buffer or object being sent. */
     time_t ctime;           /* Client creation time. */
+    long duration;          /* Current command duration. Used for measuring latency of blocking/non-blocking cmds */
     time_t lastinteraction; /* Time of the last interaction, used for timeout */
     time_t obuf_soft_limit_reached_time;
     uint64_t flags;         /* Client flags: CLIENT_* macros. */
@@ -2405,6 +2406,7 @@ void disconnectAllBlockedClients(void);
 void handleClientsBlockedOnKeys(void);
 void signalKeyAsReady(redisDb *db, robj *key, int type);
 void blockForKeys(client *c, int btype, robj **keys, int numkeys, mstime_t timeout, robj *target, struct listPos *listpos, streamID *ids);
+void updateStatsOnUnblock(client *c, long blocked_us, long reply_us);
 
 /* timeout.c -- Blocked clients timeout and connections timeout. */
 void addClientToTimeoutTable(client *c);

tests/modules/Makefile

@@ -19,6 +19,7 @@ TEST_MODULES = \
     misc.so \
     hooks.so \
     blockonkeys.so \
+    blockonbackground.so \
     scan.so \
     datatype.so \
     auth.so \

tests/modules/blockonbackground.c

@@ -0,0 +1,220 @@
+#define REDISMODULE_EXPERIMENTAL_API
+#include "redismodule.h"
+#include <stdio.h>
+#include <stdlib.h>
+#include <pthread.h>
+#include <time.h>
+#include "assert.h"
+
+#define UNUSED(x) (void)(x)
+
+/* Reply callback for blocking command BLOCK.DEBUG */
+int HelloBlock_Reply(RedisModuleCtx *ctx, RedisModuleString **argv, int argc) {
+    UNUSED(argv);
+    UNUSED(argc);
+    int *myint = RedisModule_GetBlockedClientPrivateData(ctx);
+    return RedisModule_ReplyWithLongLong(ctx,*myint);
+}
+
+/* Timeout callback for blocking command BLOCK.DEBUG */
+int HelloBlock_Timeout(RedisModuleCtx *ctx, RedisModuleString **argv, int argc) {
+    UNUSED(argv);
+    UNUSED(argc);
+    RedisModuleBlockedClient *bc = RedisModule_GetBlockedClientHandle(ctx);
+    assert(RedisModule_BlockedClientMeasureTimeEnd(bc)==REDISMODULE_OK);
+    return RedisModule_ReplyWithSimpleString(ctx,"Request timedout");
+}
+
+/* Private data freeing callback for BLOCK.DEBUG command. */
+void HelloBlock_FreeData(RedisModuleCtx *ctx, void *privdata) {
+    UNUSED(ctx);
+    RedisModule_Free(privdata);
+}
+
+/* The thread entry point that actually executes the blocking part
+ * of the command BLOCK.DEBUG. */
+void *BlockDebug_ThreadMain(void *arg) {
+    void **targ = arg;
+    RedisModuleBlockedClient *bc = targ[0];
+    long long delay = (unsigned long)targ[1];
+    long long enable_time_track = (unsigned long)targ[2];
+    if (enable_time_track)
+        assert(RedisModule_BlockedClientMeasureTimeStart(bc)==REDISMODULE_OK);
+    RedisModule_Free(targ);
+
+    struct timespec ts;
+    ts.tv_sec = delay / 1000;
+    ts.tv_nsec = (delay % 1000) * 1000000;
+    nanosleep(&ts, NULL);
+    int *r = RedisModule_Alloc(sizeof(int));
+    *r = rand();
+    if (enable_time_track)
+        assert(RedisModule_BlockedClientMeasureTimeEnd(bc)==REDISMODULE_OK);
+    RedisModule_UnblockClient(bc,r);
+    return NULL;
+}
+
+/* The thread entry point that actually executes the blocking part
+ * of the command BLOCK.DEBUG. */
+void *DoubleBlock_ThreadMain(void *arg) {
+    void **targ = arg;
+    RedisModuleBlockedClient *bc = targ[0];
+    long long delay = (unsigned long)targ[1];
+    assert(RedisModule_BlockedClientMeasureTimeStart(bc)==REDISMODULE_OK);
+    RedisModule_Free(targ);
+    struct timespec ts;
+    ts.tv_sec = delay / 1000;
+    ts.tv_nsec = (delay % 1000) * 1000000;
+    nanosleep(&ts, NULL);
+    int *r = RedisModule_Alloc(sizeof(int));
+    *r = rand();
+    RedisModule_BlockedClientMeasureTimeEnd(bc);
+    /* call again RedisModule_BlockedClientMeasureTimeStart() and
+     * RedisModule_BlockedClientMeasureTimeEnd and ensure that the
+     * total execution time is 2x the delay. */
+    assert(RedisModule_BlockedClientMeasureTimeStart(bc)==REDISMODULE_OK);
+    nanosleep(&ts, NULL);
+    RedisModule_BlockedClientMeasureTimeEnd(bc);
+
+    RedisModule_UnblockClient(bc,r);
+    return NULL;
+}
+
+void HelloBlock_Disconnected(RedisModuleCtx *ctx, RedisModuleBlockedClient *bc) {
+    RedisModule_Log(ctx,"warning","Blocked client %p disconnected!",
+        (void*)bc);
+}
+
+/* BLOCK.DEBUG <delay_ms> <timeout_ms> -- Block for <count> milliseconds, then reply with
+ * a random number. Timeout is the command timeout, so that you can test
+ * what happens when the delay is greater than the timeout. */
+int HelloBlock_RedisCommand(RedisModuleCtx *ctx, RedisModuleString **argv, int argc) {
+    if (argc != 3) return RedisModule_WrongArity(ctx);
+    long long delay;
+    long long timeout;
+
+    if (RedisModule_StringToLongLong(argv[1],&delay) != REDISMODULE_OK) {
+        return RedisModule_ReplyWithError(ctx,"ERR invalid count");
+    }
+
+    if (RedisModule_StringToLongLong(argv[2],&timeout) != REDISMODULE_OK) {
+        return RedisModule_ReplyWithError(ctx,"ERR invalid count");
+    }
+
+    pthread_t tid;
+    RedisModuleBlockedClient *bc = RedisModule_BlockClient(ctx,HelloBlock_Reply,HelloBlock_Timeout,HelloBlock_FreeData,timeout);
+
+    /* Here we set a disconnection handler, however since this module will
+     * block in sleep() in a thread, there is not much we can do in the
+     * callback, so this is just to show you the API. */
+    RedisModule_SetDisconnectCallback(bc,HelloBlock_Disconnected);
+
+    /* Now that we setup a blocking client, we need to pass the control
+     * to the thread. However we need to pass arguments to the thread:
+     * the delay and a reference to the blocked client handle. */
+    void **targ = RedisModule_Alloc(sizeof(void*)*3);
+    targ[0] = bc;
+    targ[1] = (void*)(unsigned long) delay;
+    // pass 1 as flag to enable time tracking
+    targ[2] = (void*)(unsigned long) 1;
+
+    if (pthread_create(&tid,NULL,BlockDebug_ThreadMain,targ) != 0) {
+        RedisModule_AbortBlock(bc);
+        return RedisModule_ReplyWithError(ctx,"-ERR Can't start thread");
+    }
+    return REDISMODULE_OK;
+}
+
+/* BLOCK.DEBUG_NOTRACKING <delay_ms> <timeout_ms> -- Block for <count> milliseconds, then reply with
+ * a random number. Timeout is the command timeout, so that you can test
+ * what happens when the delay is greater than the timeout.
+ * this command does not track background time so the background time should no appear in stats*/
+int HelloBlockNoTracking_RedisCommand(RedisModuleCtx *ctx, RedisModuleString **argv, int argc) {
+    if (argc != 3) return RedisModule_WrongArity(ctx);
+    long long delay;
+    long long timeout;
+
+    if (RedisModule_StringToLongLong(argv[1],&delay) != REDISMODULE_OK) {
+        return RedisModule_ReplyWithError(ctx,"ERR invalid count");
+    }
+
+    if (RedisModule_StringToLongLong(argv[2],&timeout) != REDISMODULE_OK) {
+        return RedisModule_ReplyWithError(ctx,"ERR invalid count");
+    }
+
+    pthread_t tid;
+    RedisModuleBlockedClient *bc = RedisModule_BlockClient(ctx,HelloBlock_Reply,HelloBlock_Timeout,HelloBlock_FreeData,timeout);
+
+    /* Here we set a disconnection handler, however since this module will
+     * block in sleep() in a thread, there is not much we can do in the
+     * callback, so this is just to show you the API. */
+    RedisModule_SetDisconnectCallback(bc,HelloBlock_Disconnected);
+
+    /* Now that we setup a blocking client, we need to pass the control
+     * to the thread. However we need to pass arguments to the thread:
+     * the delay and a reference to the blocked client handle. */
+    void **targ = RedisModule_Alloc(sizeof(void*)*3);
+    targ[0] = bc;
+    targ[1] = (void*)(unsigned long) delay;
+    // pass 0 as flag to enable time tracking
+    targ[2] = (void*)(unsigned long) 0;
+
+    if (pthread_create(&tid,NULL,BlockDebug_ThreadMain,targ) != 0) {
+        RedisModule_AbortBlock(bc);
+        return RedisModule_ReplyWithError(ctx,"-ERR Can't start thread");
+    }
+    return REDISMODULE_OK;
+}
+
+/* BLOCK.DOUBLE_DEBUG <delay_ms> -- Block for 2 x <count> milliseconds,
+ * then reply with a random number.
+ * This command is used to test multiple calls to RedisModule_BlockedClientMeasureTimeStart()
+ * and RedisModule_BlockedClientMeasureTimeEnd() within the same execution. */
+int HelloDoubleBlock_RedisCommand(RedisModuleCtx *ctx, RedisModuleString **argv, int argc) {
+    if (argc != 2) return RedisModule_WrongArity(ctx);
+    long long delay;
+    long long timeout;
+
+    if (RedisModule_StringToLongLong(argv[1],&delay) != REDISMODULE_OK) {
+        return RedisModule_ReplyWithError(ctx,"ERR invalid count");
+    }
+
+    pthread_t tid;
+    RedisModuleBlockedClient *bc = RedisModule_BlockClient(ctx,HelloBlock_Reply,HelloBlock_Timeout,HelloBlock_FreeData,timeout);
+
+    /* Now that we setup a blocking client, we need to pass the control
+     * to the thread. However we need to pass arguments to the thread:
+     * the delay and a reference to the blocked client handle. */
+    void **targ = RedisModule_Alloc(sizeof(void*)*2);
+    targ[0] = bc;
+    targ[1] = (void*)(unsigned long) delay;
+
+    if (pthread_create(&tid,NULL,DoubleBlock_ThreadMain,targ) != 0) {
+        RedisModule_AbortBlock(bc);
+        return RedisModule_ReplyWithError(ctx,"-ERR Can't start thread");
+    }
+    return REDISMODULE_OK;
+}
+
+
+int RedisModule_OnLoad(RedisModuleCtx *ctx, RedisModuleString **argv, int argc) {
+    UNUSED(argv);
+    UNUSED(argc);
+
+    if (RedisModule_Init(ctx,"block",1,REDISMODULE_APIVER_1)
+        == REDISMODULE_ERR) return REDISMODULE_ERR;
+
+    if (RedisModule_CreateCommand(ctx,"block.debug",
+        HelloBlock_RedisCommand,"",0,0,0) == REDISMODULE_ERR)
+        return REDISMODULE_ERR;
+
+    if (RedisModule_CreateCommand(ctx,"block.double_debug",
+        HelloDoubleBlock_RedisCommand,"",0,0,0) == REDISMODULE_ERR)
+        return REDISMODULE_ERR;
+
+    if (RedisModule_CreateCommand(ctx,"block.debug_no_track",
+        HelloBlockNoTracking_RedisCommand,"",0,0,0) == REDISMODULE_ERR)
+        return REDISMODULE_ERR;
+
+    return REDISMODULE_OK;
+}

tests/unit/moduleapi/blockonbackground.tcl

@@ -0,0 +1,67 @@
+set testmodule [file normalize tests/modules/blockonbackground.so]
+
+source tests/support/util.tcl
+
+start_server {tags {"modules"}} {
+    r module load $testmodule
+
+    test { blocked clients time tracking - check blocked command that uses RedisModule_BlockedClientMeasureTimeStart() is tracking background time} {
+        r slowlog reset
+        r config set slowlog-log-slower-than 200000
+        assert_equal [r slowlog len] 0
+        r block.debug 0 10000
+        assert_equal [r slowlog len] 0
+        r config resetstat
+        r block.debug 200 10000
+        assert_equal [r slowlog len] 1
+
+        set cmdstatline [cmdrstat block.debug r]
+
+        regexp "calls=1,usec=(.*?),usec_per_call=(.*?),rejected_calls=0,failed_calls=0" $cmdstatline usec usec_per_call
+        assert {$usec >= 100000}
+        assert {$usec_per_call >= 100000}
+    }
+
+    test { blocked clients time tracking - check blocked command that uses RedisModule_BlockedClientMeasureTimeStart() is tracking background time even in timeout } {
+        r slowlog reset
+        r config set slowlog-log-slower-than 200000
+        assert_equal [r slowlog len] 0
+        r block.debug 0 20000
+        assert_equal [r slowlog len] 0
+        r config resetstat
+        r block.debug 20000 200
+        assert_equal [r slowlog len] 1
+
+        set cmdstatline [cmdrstat block.debug r]
+
+        regexp "calls=1,usec=(.*?),usec_per_call=(.*?),rejected_calls=0,failed_calls=0" $cmdstatline usec usec_per_call
+        assert {$usec >= 100000}
+        assert {$usec_per_call >= 100000}
+    }
+
+    test { blocked clients time tracking - check blocked command with multiple calls RedisModule_BlockedClientMeasureTimeStart()  is tracking the total background time } {
+        r slowlog reset
+        r config set slowlog-log-slower-than 200000
+        assert_equal [r slowlog len] 0
+        r block.double_debug 0
+        assert_equal [r slowlog len] 0
+        r config resetstat
+        r block.double_debug 100
+        assert_equal [r slowlog len] 1
+
+        set cmdstatline [cmdrstat block.double_debug r]
+
+        regexp "calls=1,usec=(.*?),usec_per_call=(.*?),rejected_calls=0,failed_calls=0" $cmdstatline usec usec_per_call
+        assert {$usec >= 60000}
+        assert {$usec_per_call >= 60000}
+    }
+
+    test { blocked clients time tracking - check blocked command without calling RedisModule_BlockedClientMeasureTimeStart() is not reporting background time } {
+        r slowlog reset
+        r config set slowlog-log-slower-than 200000
+        assert_equal [r slowlog len] 0
+        r block.debug_no_track 200 1000
+        # ensure slowlog is still empty
+        assert_equal [r slowlog len] 0
+    }
+}