SERVER-28380 Clear ramlog before looking for stopReplProducer failpoint log message

(cherry picked from commit 07ddacf92a2c53bd5a02878917ab8ebb35874413)

3 files changed, 72 insertions, 2 deletions

diff --git a/src/mongo/db/commands/generic.cpp b/src/mongo/db/commands/generic.cpp
index ae173c44942..be8f55b9fe5 100644
--- a/src/mongo/db/commands/generic.cpp
+++ b/src/mongo/db/commands/generic.cpp
@@ -32,6 +32,7 @@
 
 #include <time.h>
 
+#include "mongo/bson/util/bson_extract.h"
 #include "mongo/bson/util/builder.h"
 #include "mongo/client/dbclient_rs.h"
 #include "mongo/db/auth/action_set.h"
@@ -450,6 +451,61 @@ public:
 
 } getLogCmd;
 
+class ClearLogCmd : public Command {
+public:
+    ClearLogCmd() : Command("clearLog") {}
+
+    virtual bool slaveOk() const {
+        return true;
+    }
+    virtual bool supportsWriteConcern(const BSONObj& cmd) const override {
+        return false;
+    }
+    virtual bool adminOnly() const {
+        return true;
+    }
+    Status checkAuthForCommand(Client* client,
+                               const std::string& dbname,
+                               const BSONObj& cmdObj) override {
+        // No access control needed since this command is a testing-only command that must be
+        // enabled at the command line.
+        return Status::OK();
+    }
+    virtual void help(stringstream& help) const {
+        help << "{ clearLog : 'global' }";
+    }
+
+    virtual bool run(OperationContext* opCtx,
+                     const string& dbname,
+                     BSONObj& cmdObj,
+                     int,
+                     string& errmsg,
+                     BSONObjBuilder& result) {
+        std::string logName;
+        Status status = bsonExtractStringField(cmdObj, "clearLog", &logName);
+        if (!status.isOK()) {
+            return appendCommandStatus(result, status);
+        }
+
+        if (logName != "global") {
+            return appendCommandStatus(
+                result, Status(ErrorCodes::InvalidOptions, "Only the 'global' log can be cleared"));
+        }
+        RamLog* ramlog = RamLog::getIfExists(logName);
+        invariant(ramlog);
+        ramlog->clear();
+        return true;
+    }
+};
+
+MONGO_INITIALIZER(RegisterClearLogCmd)(InitializerContext* context) {
+    if (Command::testCommandsEnabled) {
+        // Leaked intentionally: a Command registers itself when constructed.
+        new ClearLogCmd();
+    }
+    return Status::OK();
+}
+
 class CmdGetCmdLineOpts : Command {
 public:
     CmdGetCmdLineOpts() : Command("getCmdLineOpts") {}
diff --git a/src/mongo/logger/ramlog.cpp b/src/mongo/logger/ramlog.cpp
index 42742f32bcc..e0190577f71 100644
--- a/src/mongo/logger/ramlog.cpp
+++ b/src/mongo/logger/ramlog.cpp
@@ -50,8 +50,7 @@ RM* _named = NULL;
 }  // namespace
 
 RamLog::RamLog(const std::string& name) : _name(name), _totalLinesWritten(0), _lastWrite(0) {
-    h = 0;
-    n = 0;
+    clear();
     for (int i = 0; i < N; i++)
         lines[i][C - 1] = 0;
 }
@@ -84,6 +83,16 @@ void RamLog::write(const std::string& str) {
         h = (h + 1) % N;
 }
 
+void RamLog::clear() {
+    stdx::lock_guard<stdx::mutex> lk(_mutex);
+    _totalLinesWritten = 0;
+    _lastWrite = 0;
+    h = 0;
+    n = 0;
+    for (int i = 0; i < N; i++)
+        lines[i][0] = 0;
+}
+
 time_t RamLog::LineIterator::lastWrite() {
     return _ramlog->_lastWrite;
 }
diff --git a/src/mongo/logger/ramlog.h b/src/mongo/logger/ramlog.h
index 54901948f74..902471c4563 100644
--- a/src/mongo/logger/ramlog.h
+++ b/src/mongo/logger/ramlog.h
@@ -93,6 +93,11 @@ public:
      */
     void write(const std::string& str);
 
+    /**
+     * Empties out the RamLog.
+     */
+    void clear();
+
 
     /**
      * Writes an HTML representation of the log to "s".