2 ms·

I think it means "entering a state where the thread has nothing to do but wait." An "add" instruction is synchronous but I wouldn't say it "blocks".

• Arnavion 3y ago
  >I think it means "entering a state where the thread has nothing to do but wait." No. Neither thread involved here (the userspace thread or the kernel thread) will "wait" in either scenario. The userspace thread will either work on the syscall (because it was ready to be performed immediately) or it will be released to go do something else. The kernel thread will either not be involved (because the syscall was performed by the userspace thread already) or it will start working on the syscall.