我遇到了一个嵌套的 for 循环，其中包含等待操作，如下所示： async handleProjects (projects) { for (let i = 0; i < projects.rows.length; i++) { projects.rows[i].owner = await this.userProvider.serialize(projects.rows[i].owner); for (let j = 0; j < projects.rows[i].collaborators.length; j++) { const collaborator = await this.userProvider.serialize(projects.rows[i].collaborators[j].email); if (collaborator) { projects.rows[i].collaborators[j].name = collaborator.name; delete projects.rows[i].collaborators[j].role; } } } return projects; }1. 上面的代码是按顺序运行的吗？2. 为了提高性能我想使用 promise.all 如下所示，但有些运行时间大致相同，有些时候 promise.all 甚至更长。我的错误在哪里？ async handleProject (projects) { await Promise.all(projects.rows.map(async (row) => { console.log(row); row.owner = await this.userProvider.serialize(row.owner); return await Promise.all(row.collaborators.map(async (collaborator) => { const collaboratorObj = await this.userProvider.serialize(collaborator.email); if (collaboratorObj) { collaborator.name = collaboratorObj.name; delete collaborator.role; } })); })); return projects; }
1 回答
叮当猫咪
TA贡献1776条经验 获得超12个赞
让我们看一下使用超时来模拟您的异步调用。
在您进行优化之前，此代码等效于您的第一个示例。请注意在任何给定时刻只有一个承诺待处理：
let serializeAndCache = owner => {
console.log(`Starting: ${owner}`);
let prm = new Promise(r => setTimeout(r, 2000));
prm.then(() => console.log(`Finished: ${owner}`));
return prm;
};
let project = {
rows: [
{
owner: 'owner1',
collaborators: [
{ name: null, email: 'collab1@row1.com' },
{ name: null, email: 'collab2@row1.com' },
{ name: null, email: 'collab3@row1.com' },
{ name: null, email: 'collab4@row1.com' }
]
},
{
owner: 'owner2',
collaborators: [
{ name: null, email: 'collab1@row2.com' },
{ name: null, email: 'collab2@row2.com' },
{ name: null, email: 'collab3@row2.com' },
{ name: null, email: 'collab4@row2.com' }
]
},
{
owner: 'owner3',
collaborators: [
{ name: null, email: 'collab1@row3.com' },
{ name: null, email: 'collab2@row3.com' },
{ name: null, email: 'collab3@row3.com' },
{ name: null, email: 'collab4@row3.com' }
]
}
]
};
(async () => {
for (let row of project.rows) {
row.owner = await serializeAndCache(row.owner);
for (let collaborator of row.collaborators) {
let c = await serializeAndCache(collaborator.email);
if (!c) continue;
collaborator.name = c.name;
delete collaborator.role;
}
}
})();
这段代码相当于你的优化版本：
let serializeAndCache = owner => {
console.log(`Starting: ${owner}`);
let prm = new Promise(r => setTimeout(r, 2000));
prm.then(() => console.log(`Finished: ${owner}`));
return prm;
};
let project = {
rows: [
{
owner: 'owner1',
collaborators: [
{ name: null, email: 'collab1@row1.com' },
{ name: null, email: 'collab2@row1.com' },
{ name: null, email: 'collab3@row1.com' },
{ name: null, email: 'collab4@row1.com' }
]
},
{
owner: 'owner2',
collaborators: [
{ name: null, email: 'collab1@row2.com' },
{ name: null, email: 'collab2@row2.com' },
{ name: null, email: 'collab3@row2.com' },
{ name: null, email: 'collab4@row2.com' }
]
},
{
owner: 'owner3',
collaborators: [
{ name: null, email: 'collab1@row3.com' },
{ name: null, email: 'collab2@row3.com' },
{ name: null, email: 'collab3@row3.com' },
{ name: null, email: 'collab4@row3.com' }
]
}
]
};
(async () => {
await Promise.all(project.rows.map(async row => {
row.owner = await serializeAndCache(row.owner);
return Promise.all(row.collaborators.map(async collab => {
let c = await serializeAndCache(collab.email);
if (c) {
collab.name = c.name;
delete collab.role;
}
}));
}));
})();
如您所见，许多 Promise 都同时处于待处理状态（总体而言，代码完成得更快）。您的优化似乎奏效了！我只能假设背后的任何逻辑serializeAndCache在同时被许多调用淹没时表现不佳。这似乎是性能不佳的唯一解释。
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