10.1 Building Multithreaded Programs

All libraries shipped with the C++ compiler are multithreading safe. If you want to build a multithreaded application, or if you want to link your application to a multithreaded library, you must compile and link your program with the –mt option. This option passes –D_REENTRANT to the preprocessor and passes –lthread in the correct order to ld. For compatibility mode (–compat[=4]), the –mt option ensures that libthread is linked before libC. For standard mode (the default mode), the -mt option ensures that libthread is linked before libCrun. Use of —mt is recommended as a simpler and less error-prone alternative to specifying the macro and library.

10.1.1 Indicating Multithreaded Compilation

You can check whether an application is linked to libthread or not by using the ldd command:

example% CC -mt myprog.cc
example% ldd a.out
libm.so.1 =>      /usr/lib/libm.so.1
libCrun.so.1 =>   /usr/lib/libCrun.so.1
libthread.so.1 => /usr/lib/libthread.so.1
libc.so.1 =>      /usr/lib/libc.so.1
libdl.so.1 =>     /usr/lib/libdl.so.1

10.1.2 Using C++ Support Libraries With Threads and Signals

The C++ support libraries, libCrun, libiostream, libCstd, and libC are multithread safe but are not async safe. This means that in a multithreaded application, functions available in the support libraries should not be used in signal handlers. Doing so can result in a deadlock situation.

It is not safe to use the following in a signal handler in a multithreaded application:

• Iostreams

• new and delete expressions

• Exceptions