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author | Joel Sherrill <joel.sherrill@OARcorp.com> | 2002-05-14 19:02:06 +0000 |
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committer | Joel Sherrill <joel.sherrill@OARcorp.com> | 2002-05-14 19:02:06 +0000 |
commit | baf7133855d07a897c5337b5860b6e9c61482d2f (patch) | |
tree | 8fa971de8e3d73a4a7a88d950566354a573f48f4 /cpukit/libcsupport/src/envlock.c | |
parent | 2002-05-03 Ralf Corsepius <corsepiu@faw.uni-ulm.de> (diff) | |
download | rtems-baf7133855d07a897c5337b5860b6e9c61482d2f.tar.bz2 |
2001-05-14 Till Straumann <strauman@slac.stanford.edu>
* Per PR212, added envlock support for newlib. This is used
by at least getenv()/putenv() to avoid race conditions.
* libc/envlock.c: New file.
* libc/Makefile.am: Modified to reflect above.
Diffstat (limited to '')
-rw-r--r-- | cpukit/libcsupport/src/envlock.c | 82 |
1 files changed, 82 insertions, 0 deletions
diff --git a/cpukit/libcsupport/src/envlock.c b/cpukit/libcsupport/src/envlock.c new file mode 100644 index 0000000000..c9489b3e88 --- /dev/null +++ b/cpukit/libcsupport/src/envlock.c @@ -0,0 +1,82 @@ +/* + * $Id$ + * + * Author: Till Straumann <strauman@slac.stanford.edu>, 3/2002 + */ + +/* provide locking for the global environment 'environ' */ + +#if HAVE_CONFIG_H +#include "config.h" +#endif + +#include <rtems.h> +#include <sys/reent.h> + +#include <assert.h> + +/* + * NOTES: + * - although it looks like a classical multiple-readers / single writer (MRSW) + * locking problem, we still use a single lock for the following reasons: + * 1) newlib has no provision / hook for calling different locking routines + * from setenv/putenv and getenv, respectively. + * 2) MRSW involves calling several semaphore-primitives, even in the most + * likely case of a first-reader's access. This probably takes more CPU + * time than just waiting until another reader is done; environment + * access is fast. + * - the lock implementation must allow nesting (same thread may call + * lock-lock-unlock-unlock). + * - NEWLIB-1.8.2 has an ugly BUG: if environ is NULL, _findenv_r() bails + * out leaving the lock held :-( + * + */ + +static rtems_id envLock=0; + +static void +__rtems_envlock_init(void) +{ + extern char **environ; + rtems_status_code rc; + + if (envLock) /* already initialized */ + return; + + assert(environ && "MUST have non-NULL 'environ' due to newlib bug"); + + rc = rtems_semaphore_create( + rtems_build_name('E','N','V','S'), + 1, + RTEMS_BINARY_SEMAPHORE | RTEMS_PRIORITY | RTEMS_INHERIT_PRIORITY, + 0, + &envLock); + if (RTEMS_SUCCESSFUL!=rc) + rtems_fatal_error_occurred(rc); +} + +void +__env_lock(struct _reent *r) +{ + /* Do lazy init */ + if (!envLock) + __rtems_envlock_init(); + /* + * Must not use a semaphore before pre-tasking hook is called. + * - it will corrupt memory :-( + */ + + if (_Thread_Executing) + rtems_semaphore_obtain(envLock, RTEMS_WAIT, RTEMS_NO_TIMEOUT); +} + +void +__env_unlock(struct _reent *r) +{ + /* + * Must not use a semaphore before pre-tasking hook is called. + * - it will corrupt memory :-( + */ + if (_Thread_Executing) + rtems_semaphore_release(envLock); +} |