Implementing Threads in User Space

• Thread management done by user-level threads library
• a thread library is used for management with no support from (or knowledge by) the kernel. If the kernel is single threaded, and one of the user threads blocks, then the user's process is also blocked which means that the remaining user threads are also blocked. Available for many OSes
• While user threads usually emphasize their lower management load compared to kernel threads, one must consider this in relation to their lower functionality
• Examples;
  • One quite common library is pthread - the POSIX (POSIX is an IEEE standard for a portable operating system interface based on UNIX) thread functions.
  • Mach C-threads.
  • The Sun Microsystems Solaris 2 OS provides UI-threads (a standard originating from the Unix International Organization, RIP).