77 lines
2.1 KiB
Markdown
77 lines
2.1 KiB
Markdown
`gdb` scripts
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-----------
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Originally from: https://github.com/facebook/folly/tree/593b6e76881042031b7f21d898c8e0874ea79fe0/folly/experimental/gdb
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This directory contains a collection of `gdb` scripts that we have found helpful.
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These scripts use the [gdb extension Python API](https://sourceware.org/gdb/current/onlinedocs/gdb/Python.html#Python).
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### How to run the scripts
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To run the scripts, fire up `gdb` and load a script with `source -v`. Example:
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```lang=bash
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$ gdb -p 123456
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(gdb) source -v ./folly/experimental/gdb/deadlock.py
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Type "deadlock" to detect deadlocks.
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# At this point, any new commands defined in `deadlock.py` are available.
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(gdb) deadlock
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Found deadlock!
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...
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```
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### What does each script do?
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#### `deadlock.py` - Detect deadlocks
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Consider the following program that always deadlocks:
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```lang=cpp
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void deadlock3() {
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std::mutex m1, m2, m3;
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folly::Baton<> b1, b2, b3;
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auto t1 = std::thread([&m1, &m2, &b1, &b2] {
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std::lock_guard<std::mutex> g1(m1);
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b1.post();
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b2.wait();
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std::lock_guard<std::mutex> g2(m2);
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});
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auto t2 = std::thread([&m3, &m2, &b3, &b2] {
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std::lock_guard<std::mutex> g2(m2);
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b2.post();
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b3.wait();
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std::lock_guard<std::mutex> g3(m3);
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});
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auto t3 = std::thread([&m3, &m1, &b3, &b1] {
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std::lock_guard<std::mutex> g3(m3);
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b3.post();
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b1.wait();
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std::lock_guard<std::mutex> g1(m1);
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});
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t1.join();
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t2.join();
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t3.join();
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}
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```
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The `deadlock.py` script introduces a new `deadlock` command that can help
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us identify the threads and mutexes involved with the deadlock.
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```lang=bash
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$ gdb -p 2174496
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(gdb) source -v ./folly/experimental/gdb/deadlock.py
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Type "deadlock" to detect deadlocks.
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(gdb) deadlock
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Found deadlock!
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Thread 2 (LWP 2174497) is waiting on mutex (0x00007ffcff42a4c0) held by Thread 3 (LWP 2174498)
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Thread 3 (LWP 2174498) is waiting on mutex (0x00007ffcff42a4f0) held by Thread 4 (LWP 2174499)
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Thread 4 (LWP 2174499) is waiting on mutex (0x00007ffcff42a490) held by Thread 2 (LWP 2174497)
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```
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NOTE: This script only works on Linux and requires debug symbols to be installed
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for the `pthread` library.
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