Thread Safety in C

Question

imagine I write a library in C. Further, imagine this library to be used from a multi-threaded environment. How do I make it thread-safe? More specific: How do

Answer 1

Write your own lock.

Since you're targeting PCs you're dealing with the x86 architecture which natively supplies all the multi-threading support you should need. Go over your code and identify any functions that have shared resources. Give each shared resource a 32-bit counter. Then using the interlocked operations that are implemented by the CPUs keep track of how many threads are using each shared resource and make any thread that wants to use a shared resource wait until the resource is released.

Here's a really good blog post about interlocked operations: Using Interlocked Instructions from C/C++

The author focuses mostly on using the Win32 Interlocked wrappers, but pretty much every operating system has their own wrappers for the interlocked operations, and you can always write the assembly (each of these operations is only one instruction).