diff --git a/packages/hydrojudge/src/checkers.ts b/packages/hydrojudge/src/checkers.ts
index 46e3d868..db0f72a6 100644
--- a/packages/hydrojudge/src/checkers.ts
+++ b/packages/hydrojudge/src/checkers.ts
@@ -1,7 +1,7 @@
 /* eslint-disable no-template-curly-in-string */
 import { STATUS } from '@hydrooj/utils/lib/status';
 import { FormatError, SystemError } from './error';
-import { CopyInFile, run } from './sandbox';
+import { CopyInFile, runQueued } from './sandbox';
 import { parse } from './testlib';
 
 export interface CheckConfig {
@@ -54,7 +54,7 @@ function parseDiffMsg(msg: string) {
 
 const checkers: Record<string, Checker> = new Proxy({
     async default(config) {
-        const { stdout } = await run('/usr/bin/diff -BZ usrout answer', {
+        const { stdout } = await runQueued('/usr/bin/diff -BZ usrout answer', {
             copyIn: {
                 usrout: config.user_stdout,
                 answer: config.output,
@@ -76,7 +76,7 @@ const checkers: Record<string, Checker> = new Proxy({
     },
 
     async strict(config) {
-        const { stdout } = await run('/usr/bin/diff usrout answer', {
+        const { stdout } = await runQueued('/usr/bin/diff usrout answer', {
             copyIn: {
                 usrout: config.user_stdout,
                 answer: config.output,
@@ -98,7 +98,7 @@ const checkers: Record<string, Checker> = new Proxy({
      * exit code：返回判断结果
      */
     async hustoj(config) {
-        const { code, stdout } = await run(`${config.execute} input answer usrout`, {
+        const { code, stdout } = await runQueued(`${config.execute} input answer usrout`, {
             copyIn: {
                 usrout: config.user_stdout,
                 answer: config.output,
@@ -123,7 +123,7 @@ const checkers: Record<string, Checker> = new Proxy({
      * argv[6]：输出错误报告的文件
      */
     async lemon(config) {
-        const { files, code } = await run(`${config.execute} input usrout answer ${config.score} score message`, {
+        const { files, code } = await runQueued(`${config.execute} input usrout answer ${config.score} score message`, {
             copyIn: {
                 usrout: config.user_stdout,
                 answer: config.output,
@@ -156,7 +156,7 @@ const checkers: Record<string, Checker> = new Proxy({
      * exit code：返回判断结果
      */
     async qduoj(config) {
-        const { status, stdout } = await run(`${config.execute} input usrout`, {
+        const { status, stdout } = await runQueued(`${config.execute} input usrout`, {
             copyIn: {
                 usrout: config.user_stdout,
                 input: config.input,
@@ -182,7 +182,7 @@ const checkers: Record<string, Checker> = new Proxy({
      */
     async syzoj(config) {
         // eslint-disable-next-line prefer-const
-        let { status, stdout, stderr } = await run(config.execute, {
+        let { status, stdout, stderr } = await runQueued(config.execute, {
             copyIn: {
                 input: config.input,
                 user_out: config.user_stdout,
@@ -198,7 +198,7 @@ const checkers: Record<string, Checker> = new Proxy({
     },
 
     async testlib(config) {
-        const { stderr, status, code } = await run(`${config.execute} /w/in /w/user_out /w/answer`, {
+        const { stderr, status, code } = await runQueued(`${config.execute} /w/in /w/user_out /w/answer`, {
             copyIn: {
                 in: config.input,
                 user_out: config.user_stdout,
diff --git a/packages/hydrojudge/src/compile.ts b/packages/hydrojudge/src/compile.ts
index 43078149..ff1239fe 100644
--- a/packages/hydrojudge/src/compile.ts
+++ b/packages/hydrojudge/src/compile.ts
@@ -5,7 +5,7 @@ import checkers from './checkers';
 import { CompileError, FormatError } from './error';
 import { Execute } from './interface';
 import {
-    CopyIn, CopyInFile, del, run,
+    CopyIn, CopyInFile, del, runQueued,
 } from './sandbox';
 import { compilerText } from './utils';
 
@@ -17,7 +17,7 @@ export default async function compile(
     if (lang.compile) {
         const {
             status, stdout, stderr, fileIds,
-        } = await run(
+        } = await runQueued(
             copyIn['compile.sh'] ? '/bin/bash compile.sh' : lang.compile,
             {
                 copyIn: { ...copyIn, [lang.code_file]: code },
@@ -26,6 +26,7 @@ export default async function compile(
                 time: lang.compile_time_limit || 10000,
                 memory: lang.compile_memory_limit || 256 * 1024 * 1024,
             },
+            3,
         );
         if (status === STATUS.STATUS_TIME_LIMIT_EXCEEDED) next?.({ message: 'Compile timeout.' });
         if (status === STATUS.STATUS_MEMORY_LIMIT_EXCEEDED) next?.({ message: 'Compile memory limit exceeded.' });
diff --git a/packages/hydrojudge/src/config.ts b/packages/hydrojudge/src/config.ts
index cc285c4b..a3d2bb5c 100644
--- a/packages/hydrojudge/src/config.ts
+++ b/packages/hydrojudge/src/config.ts
@@ -17,6 +17,7 @@ const JudgeSettings = Schema.object({
     total_time_limit: Schema.number().default(60),
     processLimit: Schema.number().default(32),
     parallelism: Schema.number().default(2),
+    concurrency: Schema.number(),
     singleTaskParallelism: Schema.number().default(2),
     rerun: Schema.number().description('Re-Run testcase if time-limit-exceeded (max per submission)').default(0),
     rate: Schema.number().default(1),
diff --git a/packages/hydrojudge/src/hosts/builtin.ts b/packages/hydrojudge/src/hosts/builtin.ts
index 72a335aa..463fb7db 100644
--- a/packages/hydrojudge/src/hosts/builtin.ts
+++ b/packages/hydrojudge/src/hosts/builtin.ts
@@ -80,8 +80,9 @@ export async function postInit() {
             logger.debug('Record not found: %o', t);
             return;
         }
-        (new JudgeTask(session, Object.assign(rdoc, t))).handle().catch(logger.error);
+        await (new JudgeTask(session, Object.assign(rdoc, t))).handle().catch(logger.error);
     };
-    TaskModel.consume({ type: 'judge' }, handle);
+    const parallelism = Math.max(getConfig('parallelism'), 2);
+    for (let i = 1; i < parallelism; i++) TaskModel.consume({ type: 'judge' }, handle);
     TaskModel.consume({ type: 'judge', priority: { $gt: -50 } }, handle);
 }
diff --git a/packages/hydrojudge/src/judge/default.ts b/packages/hydrojudge/src/judge/default.ts
index 228db3d4..5bdd1b6b 100644
--- a/packages/hydrojudge/src/judge/default.ts
+++ b/packages/hydrojudge/src/judge/default.ts
@@ -5,7 +5,7 @@ import compile, { compileChecker } from '../compile';
 import { runFlow } from '../flow';
 import { Execute } from '../interface';
 import { Logger } from '../log';
-import { del, run } from '../sandbox';
+import { del, run, runQueued } from '../sandbox';
 import signals from '../signals';
 import { NormalizedCase } from '../utils';
 import { Context, ContextSubTask } from './interface';
@@ -14,7 +14,7 @@ const logger = new Logger('judge/default');
 
 function judgeCase(c: NormalizedCase) {
     return async (ctx: Context, ctxSubtask: ContextSubTask, runner?: Function) => {
-        const res = await run(
+        const res = await runQueued(
             ctx.execute.execute,
             {
                 stdin: { src: c.input },
@@ -63,7 +63,7 @@ function judgeCase(c: NormalizedCase) {
             if (langConfig.analysis && !ctx.analysis) {
                 ctx.analysis = true;
                 try {
-                    const r = await run(langConfig.analysis, {
+                    const r = await runQueued(langConfig.analysis, {
                         copyIn: {
                             ...ctx.execute.copyIn,
                             input: { src: c.input },
diff --git a/packages/hydrojudge/src/judge/hack.ts b/packages/hydrojudge/src/judge/hack.ts
index 98ea9911..548df6f6 100644
--- a/packages/hydrojudge/src/judge/hack.ts
+++ b/packages/hydrojudge/src/judge/hack.ts
@@ -5,7 +5,7 @@ import { STATUS } from '@hydrooj/utils/lib/status';
 import checkers from '../checkers';
 import compile, { compileChecker, compileValidator } from '../compile';
 import { Execute } from '../interface';
-import { del, run } from '../sandbox';
+import { del, run, runQueued } from '../sandbox';
 import signals from '../signals';
 import { parseMemoryMB, parseTimeMS } from '../utils';
 import { Context } from './interface';
@@ -28,7 +28,7 @@ export async function judge(ctx: Context) {
     ]);
     ctx.clean.push(() => fs.unlink(input));
     ctx.next({ status: STATUS.STATUS_JUDGING, progress: 0 });
-    const validateResult = await run(
+    const validateResult = await runQueued(
         validator.execute,
         {
             stdin: { src: input },
@@ -41,7 +41,7 @@ export async function judge(ctx: Context) {
         const message = `${validateResult.stdout || ''}\n${validateResult.stderr || ''}`.trim();
         return ctx.end({ status: STATUS.STATUS_FORMAT_ERROR, message });
     }
-    const res = await run(
+    const res = await runQueued(
         execute.execute,
         {
             stdin: { src: input },
@@ -76,9 +76,7 @@ export async function judge(ctx: Context) {
         if (code < 32) message = signals[code];
         else message = { message: 'Your program returned {0}.', params: [code] };
     }
-    await Promise.all(
-        Object.values(res.fileIds).map((id) => del(id)),
-    ).catch(() => { /* Ignore file doesn't exist */ });
+    await Promise.allSettled(Object.values(res.fileIds).map((id) => del(id)));
 
     if (message) ctx.next({ message });
 
diff --git a/packages/hydrojudge/src/judge/run.ts b/packages/hydrojudge/src/judge/run.ts
index f049902f..0ca2277b 100644
--- a/packages/hydrojudge/src/judge/run.ts
+++ b/packages/hydrojudge/src/judge/run.ts
@@ -2,7 +2,7 @@ import { STATUS } from '@hydrooj/utils/lib/status';
 import compile from '../compile';
 import { CompileError } from '../error';
 import { Logger } from '../log';
-import { run } from '../sandbox';
+import { runQueued } from '../sandbox';
 import signals from '../signals';
 import { compilerText, parseMemoryMB, parseTimeMS } from '../utils';
 import { Context } from './interface';
@@ -46,7 +46,7 @@ export const judge = async (ctx: Context) => {
     }
     ctx.clean.push(ctx.execute.clean);
     ctx.next({ status: STATUS.STATUS_JUDGING, progress: 0 });
-    const res = await run(
+    const res = await runQueued(
         ctx.execute.execute,
         {
             stdin: { content: ctx.input },
@@ -55,6 +55,7 @@ export const judge = async (ctx: Context) => {
             time: parseTimeMS(ctx.config.time || '1s') * 2,
             memory: parseMemoryMB(ctx.config.memory || '128m'),
         },
+        1,
     );
     const { code, time, memory } = res;
     let { status } = res;
@@ -85,7 +86,7 @@ export const judge = async (ctx: Context) => {
         if (langConfig.analysis) {
             try {
                 ctx.analysis = true;
-                const r = await run(langConfig.analysis, {
+                const r = await runQueued(langConfig.analysis, {
                     copyIn: {
                         ...ctx.execute.copyIn,
                         input: { content: ctx.input },
diff --git a/packages/hydrojudge/src/judge/submit_answer.ts b/packages/hydrojudge/src/judge/submit_answer.ts
index 3162252e..fda77332 100644
--- a/packages/hydrojudge/src/judge/submit_answer.ts
+++ b/packages/hydrojudge/src/judge/submit_answer.ts
@@ -4,7 +4,7 @@ import { STATUS } from '@hydrooj/utils/lib/status';
 import checkers from '../checkers';
 import { compileChecker } from '../compile';
 import { runFlow } from '../flow';
-import { del, run } from '../sandbox';
+import { del, runQueued } from '../sandbox';
 import { NormalizedCase } from '../utils';
 import { Context } from './interface';
 
@@ -20,7 +20,7 @@ function judgeCase(c: NormalizedCase) {
         let score = 0;
         const fileIds = [];
         if (ctx.config.subType === 'multi') {
-            const res = await run(
+            const res = await runQueued(
                 '/usr/bin/unzip foo.zip',
                 {
                     stdin: null,
@@ -54,7 +54,7 @@ function judgeCase(c: NormalizedCase) {
                 env: { ...ctx.env, HYDRO_TESTCASE: c.id.toString() },
             }));
         }
-        await Promise.all(fileIds.map(del)).catch(() => { /* Ignore file doesn't exist */ });
+        await Promise.allSettled(fileIds.map(del));
         return {
             id: c.id,
             status,
diff --git a/packages/hydrojudge/src/sandbox.ts b/packages/hydrojudge/src/sandbox.ts
index afe3b20c..5b22d7a6 100644
--- a/packages/hydrojudge/src/sandbox.ts
+++ b/packages/hydrojudge/src/sandbox.ts
@@ -206,10 +206,10 @@ export async function run(execute: string, params?: Parameter): Promise<SandboxA
     return await adaptResult(result, params);
 }
 
-const queue = new PQueue({ concurrency: getConfig('parallelism') });
+const queue = new PQueue({ concurrency: getConfig('concurrency') || getConfig('parallelism') });
 
 export function runQueued(execute: string, params?: Parameter, priority = 0) {
-    return queue.add(() => run(execute, params), { priority });
+    return queue.add(() => run(execute, params), { priority }) as Promise<SandboxAdaptedResult>;
 }
 
 export * from './sandbox/interface';