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* recheck cancellation disabled flag after syscall returns EINTRRich Felker2011-04-181-1/+1
| | | | | | | we already checked before making the syscall, but it's possible that a signal handler interrupted the blocking syscall and disabled cancellation, and that this is the cause of EINTR. in this case, the old behavior was testably wrong.
* clean up handling of thread/nothread mode, lockingRich Felker2011-04-171-1/+1
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* fix bugs in cancellable syscall asmRich Felker2011-04-171-1/+2
| | | | | | | | | | | | | | | | x86_64 was just plain wrong in the cancel-flag-already-set path, and crashing. the more subtle error was not clearing the saved stack pointer before returning to c code. this could result in the signal handler misidentifying c code as the pre-syscall part of the asm, and acting on cancellation at the wrong time, and thus resource leak race conditions. also, now __cancel (in the c code) is responsible for clearing the saved sp in the already-cancelled branch. this means we have to use call rather than jmp to ensure the stack pointer in the c will never match what the asm saved.
* don't use pthread_once when there is no danger in raceRich Felker2011-04-171-2/+5
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* fix some minor issues in cancellation handling patchRich Felker2011-04-171-9/+17
| | | | | signals were wrongly left masked, and cancellability state was not switched to disabled, during the execution of cleanup handlers.
* overhaul pthread cancellationRich Felker2011-04-171-0/+70
this patch improves the correctness, simplicity, and size of cancellation-related code. modulo any small errors, it should now be completely conformant, safe, and resource-leak free. the notion of entering and exiting cancellation-point context has been completely eliminated and replaced with alternative syscall assembly code for cancellable syscalls. the assembly is responsible for setting up execution context information (stack pointer and address of the syscall instruction) which the cancellation signal handler can use to determine whether the interrupted code was in a cancellable state. these changes eliminate race conditions in the previous generation of cancellation handling code (whereby a cancellation request received just prior to the syscall would not be processed, leaving the syscall to block, potentially indefinitely), and remedy an issue where non-cancellable syscalls made from signal handlers became cancellable if the signal handler interrupted a cancellation point. x86_64 asm is untested and may need a second try to get it right.