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Fix binary_semaphore_t under non-Linux TSan

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Under non-Linux builds, binary_semaphore is implemented with a
self-pipe. When TSan is active we mark the pipe as non-blocking as TSan
cannot interrupt read (but can interrupt select). However we weren't
properly testing for EAGAIN leading to an assertion failure.

Allow looping on EAGAIN.
This commit is contained in:
ridiculousfish 2021-02-06 14:39:07 -08:00
parent 736e344727
commit 9c238385f0
1 changed files with 12 additions and 10 deletions
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22
src/topic_monitor.cpp
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@ -56,6 +56,7 @@ binary_semaphore_t::binary_semaphore_t() : sem_ok_(false) {
}
binary_semaphore_t::~binary_semaphore_t() {
// We never use sem_t on Mac. The #ifdef avoids deprecation warnings.
#ifndef __APPLE__
if (sem_ok_) (void)sem_destroy(&sem_);
#endif
@ -92,21 +93,22 @@ void binary_semaphore_t::wait() {
if (res < 0) die(L"sem_wait");
} else {
int fd = pipes_.read.fd();
#ifdef TOPIC_MONITOR_TSAN_WORKAROUND
// Under tsan our notifying pipe is non-blocking, so we would busy-loop on the read() call
// until data is available (that is, fish would use 100% cpu while waiting for processes).
// The select prevents that.
fd_set fds;
FD_ZERO(&fds);
FD_SET(fd, &fds);
(void)select(fd + 1, &fds, nullptr, nullptr, nullptr /* timeout */);
#endif
// We must read exactly one byte.
for (;;) {
#ifdef TOPIC_MONITOR_TSAN_WORKAROUND
// Under tsan our notifying pipe is non-blocking, so we would busy-loop on the read()
// call until data is available (that is, fish would use 100% cpu while waiting for
// processes). The select prevents that.
fd_set fds;
FD_ZERO(&fds);
FD_SET(fd, &fds);
(void)select(fd + 1, &fds, nullptr, nullptr, nullptr /* timeout */);
#endif
uint8_t ignored;
auto amt = read(fd, &ignored, sizeof ignored);
if (amt == 1) break;
if (amt < 0 && errno != EINTR) die(L"read");
// EAGAIN should only be returned in TSan case.
if (amt < 0 && errno != EINTR && errno != EAGAIN) die(L"read");
}
}
}