## Why Does My Go C-Shared Library Hang on Network Calls in a Forked Child Process?

Debugging Go C-shared Library Problems: Hangs on Network Calls

Issue

A Go program encounters a hang when calling http.Post() while built as a C shared library (-buildmode=c-shared). However, the standard executable binary (GOOS=linux GOARCH=amd64 ./example) returns the correct value.

Source of the Problem

The issue arises because the Go runtime is loaded when the C shared library is loaded by the parent process. However, when the library is used in a forked child process, the Go runtime is not loaded correctly, leading to unpredictable behavior and hanging calls.

Debugging Steps

• Inspect system calls with strace: The strace tool can reveal system calls being made by the process. For example, running strace -fp PID may show calls to futex and Post operations, such as futex(0x7f618b2c1cd0, FUTEX_WAKE, 1) and Post().
• Add profiling to the HTTP server: To gather information about the state of the program when it hangs, add profiling to the HTTP server using http.ListenAndServe("localhost:6060", nil). This will run a profiler on port 6060, which can be inspected to identify the cause of the hang.

Solution

The solution involves controlling the loading of the Go runtime within the child process. To do this:

• Use dlopen to load the Go shared library after the child process is forked.
• Use dlsym to access symbols from the Go library within the child process.

By loading the Go runtime explicitly in the child process, it is ensured that the runtime is initialized correctly and network calls can be made successfully.

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