CMake’s FindThreads script documentation says that the variable CMAKE_USE_PTHREADS_INIT will be set “if the found thread library is pthread compatible.”
What does that mean? If it’s an actual POSIX threads implementation, then obviously it’s “pthread compatible”; but what are other “compatible” threads libraries? And what assumptions can I make about them? To take the most basic example: Can I safely include pthread.h?
tl;dr: “pthread-compatible” means you can assume it’s good old pthreads.
(Looking at the FindThreads.cmake source (as of CMake 3.28.3), the answer seems to be:)
This flag will be set if any of the following two conditions hold:
- Your system has library called
pthreadorpthreadsyou can link against; or - The following C program build successfully:
#include <pthread.h> static void* test_func(void* data) { return data; } int main(void) { pthread_t thread; pthread_create(&thread, NULL, test_func, NULL); pthread_detach(thread); pthread_cancel(thread); pthread_join(thread, NULL); pthread_atfork(NULL, NULL, NULL); pthread_exit(NULL); return 0; }
In the second case you know exactly what’s going on, so no problems there. The first case is a bit of a leap of faith, since you haven’t checked exactly what that library is – but then, so are many other library tests; you usually accept that a library calling itself foo is indeed the libfoo you are looking for.