diff --git a/hrp/boomer.go b/hrp/boomer.go
index 7bba9285..d639f981 100644
--- a/hrp/boomer.go
+++ b/hrp/boomer.go
@@ -72,15 +72,16 @@ func (b *HRPBoomer) Quit() {
 }
 
 func (b *HRPBoomer) convertBoomerTask(testcase *TestCase, rendezvousList []*Rendezvous) *boomer.Task {
-	// init session runner for testcase
-	sessionRunner, err := b.hrpRunner.NewSessionRunner(testcase)
+	// init runner for testcase
+	// this runner is shared by multiple session runners
+	caseRunner, err := b.hrpRunner.newCaseRunner(testcase)
 	if err != nil {
-		log.Error().Err(err).Msg("failed to create session runner")
+		log.Error().Err(err).Msg("failed to create runner")
 		os.Exit(1)
 	}
-	if sessionRunner.parser.plugin != nil {
+	if caseRunner.parser.plugin != nil {
 		b.pluginsMutex.Lock()
-		b.plugins = append(b.plugins, sessionRunner.parser.plugin)
+		b.plugins = append(b.plugins, caseRunner.parser.plugin)
 		b.pluginsMutex.Unlock()
 	}
 
@@ -93,7 +94,7 @@ func (b *HRPBoomer) convertBoomerTask(testcase *TestCase, rendezvousList []*Rend
 	}()
 
 	// set paramters mode for load testing
-	parametersIterator := sessionRunner.parametersIterator
+	parametersIterator := caseRunner.parametersIterator
 	parametersIterator.SetUnlimitedMode()
 
 	return &boomer.Task{
@@ -103,11 +104,13 @@ func (b *HRPBoomer) convertBoomerTask(testcase *TestCase, rendezvousList []*Rend
 			testcaseSuccess := true    // flag whole testcase result
 			transactionSuccess := true // flag current transaction result
 
+			// init session runner
+			sessionRunner := caseRunner.newSession()
+
 			if parametersIterator.HasNext() {
 				sessionRunner.updateConfigVariables(parametersIterator.Next())
 			}
 
-			sessionRunner.resetSession()
 			startTime := time.Now()
 			for _, step := range testcase.TestSteps {
 				stepResult, err := step.Run(sessionRunner)
diff --git a/hrp/parameters_test.go b/hrp/parameters_test.go
index e4bac50a..0276be91 100644
--- a/hrp/parameters_test.go
+++ b/hrp/parameters_test.go
@@ -353,7 +353,7 @@ func TestInitParametersIteratorContent(t *testing.T) {
 				ParametersSetting: nil,
 			},
 			0,
-			map[string]interface{}(nil),
+			map[string]interface{}{},
 		},
 	}
 	for _, data := range testData {
diff --git a/hrp/runner.go b/hrp/runner.go
index 76da1e75..acdda315 100644
--- a/hrp/runner.go
+++ b/hrp/runner.go
@@ -10,6 +10,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/jinzhu/copier"
 	"github.com/pkg/errors"
 	"github.com/rs/zerolog/log"
 	"golang.org/x/net/http2"
@@ -208,11 +209,23 @@ func (r *HRPRunner) Run(testcases ...ITestCase) error {
 // NewSessionRunner creates a new session runner for testcase.
 // each testcase has its own session runner
 func (r *HRPRunner) NewSessionRunner(testcase *TestCase) (*SessionRunner, error) {
+	runner, err := r.newCaseRunner(testcase)
+	if err != nil {
+		return nil, err
+	}
+
 	sessionRunner := &SessionRunner{
+		testCaseRunner: runner,
+	}
+	sessionRunner.resetSession()
+	return sessionRunner, nil
+}
+
+func (r *HRPRunner) newCaseRunner(testcase *TestCase) (*testCaseRunner, error) {
+	runner := &testCaseRunner{
 		testCase:  testcase,
 		hrpRunner: r,
 		parser:    newParser(),
-		summary:   newSummary(),
 	}
 
 	// init parser plugin
@@ -220,12 +233,80 @@ func (r *HRPRunner) NewSessionRunner(testcase *TestCase) (*SessionRunner, error)
 	if err != nil {
 		return nil, errors.Wrap(err, "init plugin failed")
 	}
-	sessionRunner.parser.plugin = plugin
+	runner.parser.plugin = plugin
 
 	// parse testcase config
-	if err := sessionRunner.parseConfig(); err != nil {
+	if err := runner.parseConfig(); err != nil {
 		return nil, errors.Wrap(err, "parse testcase config failed")
 	}
 
-	return sessionRunner, nil
+	return runner, nil
+}
+
+type testCaseRunner struct {
+	testCase           *TestCase
+	hrpRunner          *HRPRunner
+	parser             *Parser
+	parsedConfig       *TConfig
+	parametersIterator *ParametersIterator
+}
+
+// parseConfig parses testcase config, stores to parsedConfig.
+func (r *testCaseRunner) parseConfig() error {
+	cfg := r.testCase.Config
+
+	r.parsedConfig = &TConfig{}
+	// deep copy config to avoid data racing
+	if err := copier.Copy(r.parsedConfig, cfg); err != nil {
+		log.Error().Err(err).Msg("copy testcase config failed")
+		return err
+	}
+
+	// parse config variables
+	parsedVariables, err := r.parser.ParseVariables(cfg.Variables)
+	if err != nil {
+		log.Error().Interface("variables", cfg.Variables).Err(err).Msg("parse config variables failed")
+		return err
+	}
+	r.parsedConfig.Variables = parsedVariables
+
+	// parse config name
+	parsedName, err := r.parser.ParseString(cfg.Name, parsedVariables)
+	if err != nil {
+		return errors.Wrap(err, "parse config name failed")
+	}
+	r.parsedConfig.Name = convertString(parsedName)
+
+	// parse config base url
+	parsedBaseURL, err := r.parser.ParseString(cfg.BaseURL, parsedVariables)
+	if err != nil {
+		return errors.Wrap(err, "parse config base url failed")
+	}
+	r.parsedConfig.BaseURL = convertString(parsedBaseURL)
+
+	// ensure correction of think time config
+	r.parsedConfig.ThinkTimeSetting.checkThinkTime()
+
+	// parse testcase config parameters
+	parametersIterator, err := initParametersIterator(r.parsedConfig)
+	if err != nil {
+		log.Error().Err(err).
+			Interface("parameters", r.parsedConfig.Parameters).
+			Interface("parametersSetting", r.parsedConfig.ParametersSetting).
+			Msg("parse config parameters failed")
+		return errors.Wrap(err, "parse testcase config parameters failed")
+	}
+	r.parametersIterator = parametersIterator
+
+	return nil
+}
+
+// each boomer task initiates a new session
+// in order to avoid data racing
+func (r *testCaseRunner) newSession() *SessionRunner {
+	sessionRunner := &SessionRunner{
+		testCaseRunner: r,
+	}
+	sessionRunner.resetSession()
+	return sessionRunner
 }
diff --git a/hrp/session.go b/hrp/session.go
index 05621d09..4d120cc5 100644
--- a/hrp/session.go
+++ b/hrp/session.go
@@ -4,7 +4,6 @@ import (
 	_ "embed"
 	"time"
 
-	"github.com/jinzhu/copier"
 	"github.com/pkg/errors"
 	"github.com/rs/zerolog/log"
 )
@@ -12,12 +11,8 @@ import (
 // SessionRunner is used to run testcase and its steps.
 // each testcase has its own SessionRunner instance and share session variables.
 type SessionRunner struct {
-	testCase           *TestCase
-	hrpRunner          *HRPRunner
-	parser             *Parser
-	parsedConfig       *TConfig
-	parametersIterator *ParametersIterator
-	sessionVariables   map[string]interface{}
+	*testCaseRunner
+	sessionVariables map[string]interface{}
 	// transactions stores transaction timing info.
 	// key is transaction name, value is map of transaction type and time, e.g. start time and end time.
 	transactions map[string]map[transactionType]time.Time
@@ -30,6 +25,7 @@ func (r *SessionRunner) resetSession() {
 	r.sessionVariables = make(map[string]interface{})
 	r.transactions = make(map[string]map[transactionType]time.Time)
 	r.startTime = time.Now()
+	r.summary = newSummary()
 }
 
 func (r *SessionRunner) GetParser() *Parser {
@@ -122,56 +118,6 @@ func (r *SessionRunner) updateConfigVariables(parameters map[string]interface{})
 	}
 }
 
-// parseConfig parses testcase config, stores to parsedConfig.
-func (r *SessionRunner) parseConfig() error {
-	cfg := r.testCase.Config
-
-	r.parsedConfig = &TConfig{}
-	// deep copy config to avoid data racing
-	if err := copier.Copy(r.parsedConfig, cfg); err != nil {
-		log.Error().Err(err).Msg("copy testcase config failed")
-		return err
-	}
-
-	// parse config variables
-	parsedVariables, err := r.parser.ParseVariables(cfg.Variables)
-	if err != nil {
-		log.Error().Interface("variables", cfg.Variables).Err(err).Msg("parse config variables failed")
-		return err
-	}
-	r.parsedConfig.Variables = parsedVariables
-
-	// parse config name
-	parsedName, err := r.parser.ParseString(cfg.Name, parsedVariables)
-	if err != nil {
-		return errors.Wrap(err, "parse config name failed")
-	}
-	r.parsedConfig.Name = convertString(parsedName)
-
-	// parse config base url
-	parsedBaseURL, err := r.parser.ParseString(cfg.BaseURL, parsedVariables)
-	if err != nil {
-		return errors.Wrap(err, "parse config base url failed")
-	}
-	r.parsedConfig.BaseURL = convertString(parsedBaseURL)
-
-	// ensure correction of think time config
-	r.parsedConfig.ThinkTimeSetting.checkThinkTime()
-
-	// parse testcase config parameters
-	parametersIterator, err := initParametersIterator(r.parsedConfig)
-	if err != nil {
-		log.Error().Err(err).
-			Interface("parameters", r.parsedConfig.Parameters).
-			Interface("parametersSetting", r.parsedConfig.ParametersSetting).
-			Msg("parse config parameters failed")
-		return errors.Wrap(err, "parse testcase config parameters failed")
-	}
-	r.parametersIterator = parametersIterator
-
-	return nil
-}
-
 func (r *SessionRunner) GetSummary() *TestCaseSummary {
 	caseSummary := r.summary
 	caseSummary.Name = r.parsedConfig.Name