diff options
Diffstat (limited to 'src/core/lib/iomgr/lockfree_event.cc')
| -rw-r--r-- | src/core/lib/iomgr/lockfree_event.cc | 127 |
1 files changed, 67 insertions, 60 deletions
diff --git a/src/core/lib/iomgr/lockfree_event.cc b/src/core/lib/iomgr/lockfree_event.cc index 2376165d7e..288e597c29 100644 --- a/src/core/lib/iomgr/lockfree_event.cc +++ b/src/core/lib/iomgr/lockfree_event.cc @@ -26,92 +26,96 @@ extern grpc_tracer_flag grpc_polling_trace; /* 'state' holds the to call when the fd is readable or writable respectively. It can contain one of the following values: - CLOSURE_READY : The fd has an I/O event of interest but there is no + kClosureReady : The fd has an I/O event of interest but there is no closure yet to execute - CLOSURE_NOT_READY : The fd has no I/O event of interest + kClosureNotReady : The fd has no I/O event of interest closure ptr : The closure to be executed when the fd has an I/O event of interest - shutdown_error | FD_SHUTDOWN_BIT : - 'shutdown_error' field ORed with FD_SHUTDOWN_BIT. + shutdown_error | kShutdownBit : + 'shutdown_error' field ORed with kShutdownBit. This indicates that the fd is shutdown. Since all memory allocations are word-aligned, the lower two bits of the shutdown_error pointer are always 0. So - it is safe to OR these with FD_SHUTDOWN_BIT + it is safe to OR these with kShutdownBit Valid state transitions: - <closure ptr> <-----3------ CLOSURE_NOT_READY ----1----> CLOSURE_READY + <closure ptr> <-----3------ kClosureNotReady -----1-------> kClosureReady | | ^ | ^ | | | | | | | | | | +--------------4----------+ 6 +---------2---------------+ | | | | | v | - +-----5-------> [shutdown_error | FD_SHUTDOWN_BIT] <----7---------+ + +-----5-------> [shutdown_error | kShutdownBit] <-------7---------+ - For 1, 4 : See grpc_lfev_set_ready() function - For 2, 3 : See grpc_lfev_notify_on() function - For 5,6,7: See grpc_lfev_set_shutdown() function */ + For 1, 4 : See SetReady() function + For 2, 3 : See NotifyOn() function + For 5,6,7: See SetShutdown() function */ -#define CLOSURE_NOT_READY ((gpr_atm)0) -#define CLOSURE_READY ((gpr_atm)2) +namespace grpc_core { -#define FD_SHUTDOWN_BIT ((gpr_atm)1) +LockfreeEvent::LockfreeEvent() { + /* Perform an atomic store to start the state machine. -void grpc_lfev_init(gpr_atm* state) { - gpr_atm_no_barrier_store(state, CLOSURE_NOT_READY); + Note carefully that LockfreeEvent *MAY* be used whilst in a destroyed + state, while a file descriptor is on a freelist. In such a state it may + be SetReady'd, and so we need to perform an atomic operation here to + ensure no races */ + gpr_atm_no_barrier_store(&state_, kClosureNotReady); } -void grpc_lfev_destroy(gpr_atm* state) { - gpr_atm curr = gpr_atm_no_barrier_load(state); - if (curr & FD_SHUTDOWN_BIT) { - GRPC_ERROR_UNREF((grpc_error*)(curr & ~FD_SHUTDOWN_BIT)); - } else { - GPR_ASSERT(curr == CLOSURE_NOT_READY || curr == CLOSURE_READY); - } -} - -bool grpc_lfev_is_shutdown(gpr_atm* state) { - gpr_atm curr = gpr_atm_no_barrier_load(state); - return (curr & FD_SHUTDOWN_BIT) != 0; +LockfreeEvent::~LockfreeEvent() { + gpr_atm curr; + do { + curr = gpr_atm_no_barrier_load(&state_); + if (curr & kShutdownBit) { + GRPC_ERROR_UNREF((grpc_error*)(curr & ~kShutdownBit)); + } else { + GPR_ASSERT(curr == kClosureNotReady || curr == kClosureReady); + } + /* we CAS in a shutdown, no error value here. If this event is interacted + with post-deletion (see the note in the constructor) we want the bit + pattern to prevent error retention in a deleted object */ + } while (!gpr_atm_no_barrier_cas(&state_, curr, + kShutdownBit /* shutdown, no error */)); } -void grpc_lfev_notify_on(gpr_atm* state, grpc_closure* closure, - const char* variable) { +void LockfreeEvent::NotifyOn(grpc_closure* closure) { while (true) { - gpr_atm curr = gpr_atm_no_barrier_load(state); + gpr_atm curr = gpr_atm_no_barrier_load(&state_); if (GRPC_TRACER_ON(grpc_polling_trace)) { - gpr_log(GPR_ERROR, "lfev_notify_on[%s]: %p curr=%p closure=%p", variable, - state, (void*)curr, closure); + gpr_log(GPR_ERROR, "LockfreeEvent::NotifyOn: %p curr=%p closure=%p", this, + (void*)curr, closure); } switch (curr) { - case CLOSURE_NOT_READY: { - /* CLOSURE_NOT_READY -> <closure>. + case kClosureNotReady: { + /* kClosureNotReady -> <closure>. We're guaranteed by API that there's an acquire barrier before here, so there's no need to double-dip and this can be a release-only. The release itself pairs with the acquire half of a set_ready full barrier. */ - if (gpr_atm_rel_cas(state, CLOSURE_NOT_READY, (gpr_atm)closure)) { + if (gpr_atm_rel_cas(&state_, kClosureNotReady, (gpr_atm)closure)) { return; /* Successful. Return */ } break; /* retry */ } - case CLOSURE_READY: { - /* Change the state to CLOSURE_NOT_READY. Schedule the closure if + case kClosureReady: { + /* Change the state to kClosureNotReady. Schedule the closure if successful. If not, the state most likely transitioned to shutdown. We should retry. This can be a no-barrier cas since the state is being transitioned to - CLOSURE_NOT_READY; set_ready and set_shutdown do not schedule any + kClosureNotReady; set_ready and set_shutdown do not schedule any closure when transitioning out of CLOSURE_NO_READY state (i.e there is no other code that needs to 'happen-after' this) */ - if (gpr_atm_no_barrier_cas(state, CLOSURE_READY, CLOSURE_NOT_READY)) { + if (gpr_atm_no_barrier_cas(&state_, kClosureReady, kClosureNotReady)) { GRPC_CLOSURE_SCHED(closure, GRPC_ERROR_NONE); return; /* Successful. Return */ } @@ -123,8 +127,8 @@ void grpc_lfev_notify_on(gpr_atm* state, grpc_closure* closure, /* 'curr' is either a closure or the fd is shutdown(in which case 'curr' contains a pointer to the shutdown-error). If the fd is shutdown, schedule the closure with the shutdown error */ - if ((curr & FD_SHUTDOWN_BIT) > 0) { - grpc_error* shutdown_err = (grpc_error*)(curr & ~FD_SHUTDOWN_BIT); + if ((curr & kShutdownBit) > 0) { + grpc_error* shutdown_err = (grpc_error*)(curr & ~kShutdownBit); GRPC_CLOSURE_SCHED(closure, GRPC_ERROR_CREATE_REFERENCING_FROM_STATIC_STRING( "FD Shutdown", &shutdown_err, 1)); @@ -133,7 +137,8 @@ void grpc_lfev_notify_on(gpr_atm* state, grpc_closure* closure, /* There is already a closure!. This indicates a bug in the code */ gpr_log(GPR_ERROR, - "notify_on called with a previous callback still pending"); + "LockfreeEvent::NotifyOn: notify_on called with a previous " + "callback still pending"); abort(); } } @@ -142,21 +147,21 @@ void grpc_lfev_notify_on(gpr_atm* state, grpc_closure* closure, GPR_UNREACHABLE_CODE(return ); } -bool grpc_lfev_set_shutdown(gpr_atm* state, grpc_error* shutdown_err) { - gpr_atm new_state = (gpr_atm)shutdown_err | FD_SHUTDOWN_BIT; +bool LockfreeEvent::SetShutdown(grpc_error* shutdown_err) { + gpr_atm new_state = (gpr_atm)shutdown_err | kShutdownBit; while (true) { - gpr_atm curr = gpr_atm_no_barrier_load(state); + gpr_atm curr = gpr_atm_no_barrier_load(&state_); if (GRPC_TRACER_ON(grpc_polling_trace)) { - gpr_log(GPR_ERROR, "lfev_set_shutdown: %p curr=%p err=%s", state, - (void*)curr, grpc_error_string(shutdown_err)); + gpr_log(GPR_ERROR, "LockfreeEvent::SetShutdown: %p curr=%p err=%s", + &state_, (void*)curr, grpc_error_string(shutdown_err)); } switch (curr) { - case CLOSURE_READY: - case CLOSURE_NOT_READY: + case kClosureReady: + case kClosureNotReady: /* Need a full barrier here so that the initial load in notify_on doesn't need a barrier */ - if (gpr_atm_full_cas(state, curr, new_state)) { + if (gpr_atm_full_cas(&state_, curr, new_state)) { return true; /* early out */ } break; /* retry */ @@ -165,7 +170,7 @@ bool grpc_lfev_set_shutdown(gpr_atm* state, grpc_error* shutdown_err) { /* 'curr' is either a closure or the fd is already shutdown */ /* If fd is already shutdown, we are done */ - if ((curr & FD_SHUTDOWN_BIT) > 0) { + if ((curr & kShutdownBit) > 0) { GRPC_ERROR_UNREF(shutdown_err); return false; } @@ -175,7 +180,7 @@ bool grpc_lfev_set_shutdown(gpr_atm* state, grpc_error* shutdown_err) { Needs an acquire to pair with setting the closure (and get a happens-after on that edge), and a release to pair with anything loading the shutdown state. */ - if (gpr_atm_full_cas(state, curr, new_state)) { + if (gpr_atm_full_cas(&state_, curr, new_state)) { GRPC_CLOSURE_SCHED((grpc_closure*)curr, GRPC_ERROR_CREATE_REFERENCING_FROM_STATIC_STRING( "FD Shutdown", &shutdown_err, 1)); @@ -192,25 +197,25 @@ bool grpc_lfev_set_shutdown(gpr_atm* state, grpc_error* shutdown_err) { GPR_UNREACHABLE_CODE(return false); } -void grpc_lfev_set_ready(gpr_atm* state, const char* variable) { +void LockfreeEvent::SetReady() { while (true) { - gpr_atm curr = gpr_atm_no_barrier_load(state); + gpr_atm curr = gpr_atm_no_barrier_load(&state_); if (GRPC_TRACER_ON(grpc_polling_trace)) { - gpr_log(GPR_ERROR, "lfev_set_ready[%s]: %p curr=%p", variable, state, + gpr_log(GPR_ERROR, "LockfreeEvent::SetReady: %p curr=%p", &state_, (void*)curr); } switch (curr) { - case CLOSURE_READY: { + case kClosureReady: { /* Already ready. We are done here */ return; } - case CLOSURE_NOT_READY: { + case kClosureNotReady: { /* No barrier required as we're transitioning to a state that does not involve a closure */ - if (gpr_atm_no_barrier_cas(state, CLOSURE_NOT_READY, CLOSURE_READY)) { + if (gpr_atm_no_barrier_cas(&state_, kClosureNotReady, kClosureReady)) { return; /* early out */ } break; /* retry */ @@ -218,14 +223,14 @@ void grpc_lfev_set_ready(gpr_atm* state, const char* variable) { default: { /* 'curr' is either a closure or the fd is shutdown */ - if ((curr & FD_SHUTDOWN_BIT) > 0) { + if ((curr & kShutdownBit) > 0) { /* The fd is shutdown. Do nothing */ return; } /* Full cas: acquire pairs with this cas' release in the event of a spurious set_ready; release pairs with this or the acquire in notify_on (or set_shutdown) */ - else if (gpr_atm_full_cas(state, curr, CLOSURE_NOT_READY)) { + else if (gpr_atm_full_cas(&state_, curr, kClosureNotReady)) { GRPC_CLOSURE_SCHED((grpc_closure*)curr, GRPC_ERROR_NONE); return; } @@ -237,3 +242,5 @@ void grpc_lfev_set_ready(gpr_atm* state, const char* variable) { } } } + +} // namespace grpc_core |