diff options
Diffstat (limited to 'src/include/storage/latch.h')
| -rw-r--r-- | src/include/storage/latch.h | 13 |
1 files changed, 7 insertions, 6 deletions
diff --git a/src/include/storage/latch.h b/src/include/storage/latch.h index f5c7fe1ca5e..0fa572e50b0 100644 --- a/src/include/storage/latch.h +++ b/src/include/storage/latch.h @@ -33,8 +33,8 @@ * ResetLatch - Clears the latch, allowing it to be set again * WaitLatch - Waits for the latch to become set * - * WaitLatch includes a provision for timeouts (which should hopefully not - * be necessary once the code is fully latch-ified) and a provision for + * WaitLatch includes a provision for timeouts (which should be avoided + * when possible, as they incur extra overhead) and a provision for * postmaster child processes to wake up immediately on postmaster death. * See unix_latch.c for detailed specifications for the exported functions. * @@ -64,14 +64,15 @@ * will be lifted in future by inserting suitable memory barriers into * SetLatch and ResetLatch. * + * On some platforms, signals will not interrupt the latch wait primitive + * by themselves. Therefore, it is critical that any signal handler that + * is meant to terminate a WaitLatch wait calls SetLatch. + * * Note that use of the process latch (PGPROC.procLatch) is generally better * than an ad-hoc shared latch for signaling auxiliary processes. This is * because generic signal handlers will call SetLatch on the process latch * only, so using any latch other than the process latch effectively precludes - * ever registering a generic handler. Since signals have the potential to - * invalidate the latch timeout on some platforms, resulting in a - * denial-of-service, it is important to verify that all signal handlers - * within all WaitLatch-calling processes call SetLatch. + * use of any generic handler. * * * Portions Copyright (c) 1996-2012, PostgreSQL Global Development Group |