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deaa638071
Add threadsafe versions of some libc functions on FreeBSD 4.x. Register liblgcc_r_pic.a as installed for FreeBSD 5.x.
140 lines
6.1 KiB
Text
140 lines
6.1 KiB
Text
Some brief notes:
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1) This package is intended to run on FreeBSD 5.0-current or FreeBSD 4.X, i386
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processors only.
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Do not use libc_r with the linuxthreads port, and do not compile/link with the
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-pthread option (which pulls in libc_r). Rather, link with libc (which you will
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get by default).
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Compile your applications that use the linuxthreads port with the following
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command line options:
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-D_THREAD_SAFE -I/usr/local/include/pthread/linuxthreads -llthread -llgcc_r
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Note that the include (-I<path>) directive shown here should appear before any
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other include directive that would cause the compiler to find the FreeBSD file
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/usr/include/pthread.h. Using the FreeBSD pthread.h instead of the linuxthreads
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pthread.h will result in an app that fails in many odd and maybe spectacular
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ways.
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In order to facilitate porting applications which expect a libpthread, you can
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create the following symlinks if you want:
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ln -s /usr/local/lib/liblthread.a /usr/lib/libpthread.a
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ln -s /usr/local/lib/liblthread_p.a /usr/lib/libpthread_p.a
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ln -s /usr/local/lib/liblthread.so.2 /usr/lib/libpthread.so.2
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ln -s /usr/local/lib/liblthread.so.2 /usr/lib/libpthread.so
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/sbin/ldconfig -m /usr/lib
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If you do this, you can instead use:
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-D_THREAD_SAFE -I/usr/local/include/pthread/linuxthreads -lpthread -llgcc_r
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Another option is to create a custom gcc specs file that tells the linker which
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version of libgcc to use. To do this, create a file with the following in it:
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--- (/foo/specs) cut here ---
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*libgcc:
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/usr/local/lib/liblgcc_r.a
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--- (/foo/specs) cut here ---
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Then use the following command line options:
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-B/foo/ -D_THREAD_SAFE -I/usr/local/include/pthread/linuxthreads -llthread
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or if you created symlinks:
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-B/foo/ -D_THREAD_SAFE -I/usr/local/include/pthread/linuxthreads -lpthread
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2) If you plan on having lots of threads, check the sysctl value of
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kern.maxproc. Each kernel thread counts against maxproc. You can increase
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maxproc by changing the MAXUSERS value in your kernel config file. maxproc is
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set at 20 + 16 * MAXUSERS.
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3) Be aware of the following libc issues:
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a) Not all libc calls are thread safe. In particular gmtime, localtime, etc
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are not thread safe. In general, where the pthreads spec calls for "_r"
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functions, these are either not provided, or if provided are not thread safe
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(in most cases) and the related libc calls are not thread safe. This differs
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somewhat from the FreeBSD libc_r library, where some, but not all, of these
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functions are both thread safe and have "_r" versions.
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b) Not all of the libc calls that are supposed to be cancellation points are
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implemented as such. While linux threads has the cancel functions
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implemented, deferred cancellation will not work as required by POSIX
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1003.1c-1995, since the co-operation needed from libc is not complete.
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c) The mutex wrapper functions only provide standard linuxthreads mutexes
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(i.e. non-recursive mutexes). This might lead to deadlocks if libc
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depends on recursive mutexes.
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4) Be aware of the following libgcc issue:
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FreeBSD 4.* (gcc 2.*):
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__register_frame_info() and __get_eh_info() from libgcc.a are linked
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into shared libraries that use exceptions, e.g. libstdc++. Those
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functions are not compatible with linuxthreads due to pthread_mutex_t
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and pthread_once_t having different sizes and static initializers.
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Linking the shared linuxthreads library before any such library causes
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the liblgcc_r.a version of those functions to be used.
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FreeBSD 5.* (gcc 3.*):
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__register_frame_info() and __frame_state_for() from libgcc.a are
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linked into shared libraries that use exceptions, e.g. libstdc++.
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Those functions are not compatible with linuxthreads due to
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pthread_mutex_t and pthread_once_t having different sizes and static
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initializers. Linking the shared linuxthreads library before any such
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library causes the liblgcc_r.a version of those functions to be used.
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Use liblstdc++ and liblsupc++.
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Experimental wrapper support:
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If the linuxthreads library has been compiled with
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LINUXTHREADS_WRAP_API defined in the ports makefile then
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the API functions are internally prefixed with linuxthreads_
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to avoid conflict with native threads. Weak symbols without
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that prefix points to the wrapper functions (internally
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prefixed by _) that makes the linuxthreads functions available
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with the native threads API. Applications including the
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linuxthreads version of pthread.h will try to call the
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prefixed methods (e.g. linuxthreads_pthread_create) while
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applications including the native pthread.h will use the
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wrapper functions. This allows for some level of coexistence
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of libraries compiled with linuxthreads header file and
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libraries compiled with native threads header files as long
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as none of the pthread data types leaks out as function arguments
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or structure members.
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5) Exit handling is broken.
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If the linuxthreads library has been compiled with
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LINUXTHREADS_DETECT_UNSAFE_EXIT defined in the ports makefile then
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the library tries to avoid further calls to functions registered
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with atexit if not called from the main thread or if other threads
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were active. Since this implicitly indicates a failure to do
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proper cleanup, the exit code is then changed to 1.
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If the linuxthreads library has been compiled without
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LINUXTHREADS_DETECT_UNSAFE_EXIT, then calls to exit() has a
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slightly higher probability of crashing or hanging the program when
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other threads are active. If another thread than the main thread
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performs the exit call, the exit code will appear to be 0.
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If multiple threads calls exit then the application will likely
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crash.
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If other threads has been joined by the main thread before it calls
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exit then exit handling should be fairly safe and the correct exit
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code can be detected by the parent process.
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6) If the rate of sched_yield() calls is very high (due to
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malloc / spinlock interaction) then
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LINUXTHREADS_NO_POSIX_PRIORITY_SCHEDULING can be defined when
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compiling the linuxthreads library. This has the same effect
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as if the kernel was compiled without the _KPOSIX_PRIORITY_SCHEDULING
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option, but limited to the linuxthread library.
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