diff options
| author | jtc <jtc@NetBSD.org> | 1998-01-16 10:15:08 +0000 |
|---|---|---|
| committer | jtc <jtc@NetBSD.org> | 1998-01-16 10:15:08 +0000 |
| commit | 3f4892e0d9aebb17eab67b81d36ff26ebaecbae9 (patch) | |
| tree | 36dcf9a96cb48a9859bb0a775e81a1a92dbff4b5 /lib/libc/include | |
| parent | 123d97732f424f564a73caa0d6c0206cfe987f89 (diff) | |
Header file which describes mechanism that will be used by libc for
thread safety of library internals.
Diffstat (limited to 'lib/libc/include')
| -rw-r--r-- | lib/libc/include/reentrant.h | 106 |
1 files changed, 106 insertions, 0 deletions
diff --git a/lib/libc/include/reentrant.h b/lib/libc/include/reentrant.h new file mode 100644 index 00000000000..f3a84c33d84 --- /dev/null +++ b/lib/libc/include/reentrant.h @@ -0,0 +1,106 @@ +/*- + * Copyright (c) 1997,98 The NetBSD Foundation, Inc. + * All rights reserved. + * + * This code is derived from software contributed to The NetBSD Foundation + * by J.T. Conklin. + * + * Redistribution and use in source and binary forms, with or without + * modification, are permitted provided that the following conditions + * are met: + * 1. Redistributions of source code must retain the above copyright + * notice, this list of conditions and the following disclaimer. + * 2. Redistributions in binary form must reproduce the above copyright + * notice, this list of conditions and the following disclaimer in the + * documentation and/or other materials provided with the distribution. + * 3. All advertising materials mentioning features or use of this software + * must display the following acknowledgement: + * This product includes software developed by the NetBSD + * Foundation, Inc. and its contributors. + * 4. Neither the name of The NetBSD Foundation nor the names of its + * contributors may be used to endorse or promote products derived + * from this software without specific prior written permission. + * + * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS + * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED + * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR + * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS + * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR + * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF + * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS + * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN + * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) + * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE + * POSSIBILITY OF SUCH DAMAGE. + */ + +/* + * Requirements: + * + * 1. The thread safe mechanism should be lightweight so the library can + * be used by non-threaded applications without unreasonable overhead. + * + * 2. There should be no dependency on a thread engine for non-threaded + * applications. + * + * 3. There should be no dependency on any particular thread engine. + * + * 4. The library should be able to be compiled without support for thread + * safety. + * + * + * Rationale: + * + * One approach for thread safety is to provide discrete versions of the + * library: one thread safe, the other not. The disadvantage of this is + * that libc is rather large, and two copies of a library which are 99%+ + * identical is not an efficent use of resources. + * + * Another approach is to provide a single thread safe library. However, + * it should not add significant run time or code size overhead to non- + * threaded applications. + * + * Since the NetBSD C library is used in other projects, it should be + * easy to replace the mutual exclusion primitives with ones provided by + * another system. Similarly, it should also be easy to remove all + * support for thread safety completely if the target environment does + * not support threads. + * + * + * Implementation Details: + * + * The mutex primitives used by the library (mutex_t, mutex_lock, etc.) + * are macros which expand to the cooresponding primitives provided by + * the thread engine or to nothing. The latter is used so that code is + * not unreasonably cluttered with #ifdefs when all thread safe support + * is removed. + * + * The mutex macros can be directly mapped to the mutex primitives from + * pthreads, however it should be reasonably easy to wrap another mutex + * implementation so it presents a similar interface. + * + * Stub implementations of the mutex functions are provided with *weak* + * linkage. These functions simply return success. When linked with a + * thread library (i.e. -lpthread), the functions will override the + * stubs. + */ + +/* FIXME: Using _REENT during integration testing. It should be changed + to _REENTRANT once pthread engine is available */ + +#ifdef _REENT + +#include <pthread.h> + +#define mutex_t pthread_mutex_t +#define MUTEX_INITIALIZER PTHREAD_MUTEX_INITIALIZER + +#define mutex_lock(m) pthread_mutex_lock(m) +#define mutex_unlock(m) pthread_mutex_unlock(m) + +#else + +#define mutex_lock(m) do { } while(0) +#define mutex_unlock(m) do { } while(0) + +#endif |
