Here are a few potential titles, building on the key points and question format you requested: * **Why Does My Go Shared Library Hang on http.Post() After Forking?** * **Debugging a Go Shared Library

How to Debug a C Shared Library (Written in Go) that Hangs on net.Post()

Introduction

Encountering a shared library written in Go that halts during http.Post() calls requires thorough debugging to determine the root cause. This article delves into a specific instance of this issue and the steps taken to resolve it.

Problem Description

The problem involves a Go library built as a C shared library (-buildmode=c-shared) that functions flawlessly as an executable but experiences issues when accessed as a shared library, namely, it hangs indefinitely on https.Post(). Attempts to debug using various methods, including strace and profiling, yielded inconclusive results.

Debugging

Examination of the issue revealed that the shared library is correctly built and the code appears valid. As a workaround, the issue was narrowed down to situations that utilized http.Post() or net.Dial().

Solution

The key to resolving the problem lies in the fact that when linking a Go C shared library to a C or C application, the Go runtime is loaded when the application starts. However, if a process is forked and the Go library is accessed, unexpected behavior can occur.

The fundamental rule is that the Go shared library must be loaded after the fork occurs. Relying on the library after forking can lead to unpredictable results.

Implementation

To implement this solution, dlopen and dlsym can be used to control when the Go runtime is loaded. By delaying the loading of the Go shared library until after the fork, the hanging issue was eliminated.

Conclusion

Resolving this issue required understanding the mechanics of Go runtime loading in a shared library context. By controlling when the library is loaded, it becomes possible to avoid potential conflicts after forking, ensuring the proper functioning of http.Post() and other networking-related methods.

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