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threadIdx、blockIdx、blockDim

用于定位线程的内置变量

threadIdx、blockIdx、blockDim 是 CoddyKit 上的免费 CUDA Academy 课时。这是第 2 节课，共 4 节。你可以在下方免费阅读本课时的完整内容 — 然后在浏览器中使用内置代码编辑器和全天候 AI 导师进行实践。这是 CUDA Academy 学习路径的一部分，你的进度在网页和 CoddyKit 应用中同步。 CUDA Academy 课程共包含 4 节课。

本课时的部分内容尚未翻译，以英文显示。

Where Am I?

Every thread runs the same code, so each one needs to ask: which piece of data is mine? CUDA answers with built-in variables. 📍

Meet threadIdx

Inside a kernel, threadIdx tells a thread its position within its own block. The first thread in a block has threadIdx.x equal to 0.

int t = threadIdx.x;

Meet blockIdx

The variable blockIdx tells a thread which block it belongs to within the grid. Block numbering also starts at 0.

int b = blockIdx.x;

Meet blockDim

You also get blockDim, the number of threads per block. If you launched 256 threads, then blockDim.x is 256 for every thread.

int width = blockDim.x;

They Are Automatic

You never set these variables yourself. CUDA fills them in for each thread the moment the kernel launches.

The .x, .y, .z Fields

Each of these has x, y, and z fields for 1D, 2D, or 3D launches. For simple arrays you usually only touch the x field.

Combining Them

On their own, threadIdx repeats in every block. To get a unique spot you must combine blockIdx and blockDim with threadIdx.

A Tiny Walkthrough

With blockDim 4, thread 2 in block 0 is element 2, but thread 2 in block 1 is element 6. The block shifts the start point.

Read-Only Helpers

These built-ins are read-only inside the kernel. Treat them as trusted coordinates describing exactly where your thread sits.

Also gridDim

There is one more friend: gridDim holds the total number of blocks in the grid. It is handy when you loop over more data than threads.

int blocks = gridDim.x;

Why It Matters

These three variables are the raw materials for computing a global index, which is how every thread claims its own element.

Quick Check

Pick the variable that does the stated job.

Recap: Locating a Thread

You met the built-ins: threadIdx for position in a block, blockIdx for the block, and blockDim for block size. Together they pinpoint a thread. ✅

常见问题解答

「threadIdx、blockIdx、blockDim」课时是免费的吗？

是的 — 「threadIdx、blockIdx、blockDim」的完整文本可在网页上免费阅读。要进行交互式练习（内置代码编辑器和全天候 AI 导师）并解锁 CUDA Academy 课程的其余内容，请升级到 CoddyKit PRO。 CUDA Academy 课程共包含 4 节课。

「threadIdx、blockIdx、blockDim」这节课中我会学到什么？

用于定位线程的内置变量你通过在浏览器中直接运行的动手代码来练习 CUDA Academy，全天候 AI 导师会在你学习这节课的过程中回答你的问题。

学习 CUDA Academy 需要有经验吗？

无需任何先前经验。CoddyKit 上的 CUDA Academy 课程适合初学者到高级学习者，你可以从这里开始或从头开始，按照自己的节奏学习。这是第 2 节课，共 4 节。

「threadIdx、blockIdx、blockDim」课时需要多长时间？

大多数 CoddyKit 课程大约需要 5–10 分钟。每节课都很精短且互动，所以你能稳步进步，并在网页和应用中从离开的地方继续。

我能在这节 CUDA Academy 课中编写并运行代码吗？

能。每节 CUDA Academy 课都包含内置代码编辑器，你可以在浏览器中直接编写并运行真实代码，并获得即时 AI 反馈 — 无需本地设置。

此课程中的所有课时

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