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Improve comments and code clarity.

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This commit is contained in:
Vytautas Astrauskas 2020-04-26 21:13:33 -07:00
parent 9ba3ef2a44
commit 207c6e7fa7
2 changed files with 11 additions and 7 deletions
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16
src/shims/sync.rs
View file

@ -80,7 +80,8 @@ fn mutexattr_set_kind<'mir, 'tcx: 'mir>(
// bytes 8-11: when count > 0, id of the owner thread as a u32
// bytes 12-15 or 16-19 (depending on platform): mutex kind, as an i32
// (the kind has to be at its offset for compatibility with static initializer macros)
// bytes 20-23: when count > 0, id of the blockset in which the blocked threads are waiting.
// bytes 20-23: when count > 0, id of the blockset in which the blocked threads
// are waiting or 0 if blockset is not yet assigned.
const PTHREAD_MUTEX_T_MIN_SIZE: u64 = 24;
@ -170,9 +171,9 @@ fn mutex_get_or_create_blockset<'mir, 'tcx: 'mir>(
// bytes 4-7: reader count, as a u32
// bytes 8-11: writer count, as a u32
// bytes 12-15: when writer or reader count > 0, id of the blockset in which the
// blocked writers are waiting.
// blocked writers are waiting or 0 if blockset is not yet assigned.
// bytes 16-20: when writer count > 0, id of the blockset in which the blocked
// readers are waiting.
// readers are waiting or 0 if blockset is not yet assigned.
const PTHREAD_RWLOCK_T_MIN_SIZE: u64 = 20;
@ -342,8 +343,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
Ok(0)
} else {
// The mutex is locked. Let's check by whom.
let owner_thread: ThreadId =
mutex_get_owner(this, mutex_op)?.not_undef()?.to_u32()?.into();
let owner_thread: ThreadId = mutex_get_owner(this, mutex_op)?.to_u32()?.into();
if owner_thread != active_thread {
// Block the active thread.
let blockset = mutex_get_or_create_blockset(this, mutex_op)?;
@ -425,6 +425,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
mutex_set_owner(this, mutex_op, new_owner.to_u32_scalar())?;
} else {
// No thread is waiting on this mutex.
mutex_set_owner(this, mutex_op, Scalar::from_u32(0))?;
mutex_set_locked_count(this, mutex_op, Scalar::from_u32(0))?;
}
Ok(0)
@ -550,10 +551,13 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
Ok(0)
} else if writers != 0 {
let reader_blockset = rwlock_get_or_create_reader_blockset(this, rwlock_op)?;
rwlock_set_writers(this, rwlock_op, Scalar::from_u32(0))?;
// We are prioritizing writers here against the readers. As a
// result, not only readers can starve writers, but also writers can
// starve readers.
if let Some(_writer) = this.unblock_some_thread(writer_blockset)? {
rwlock_set_writers(this, rwlock_op, Scalar::from_u32(1))?;
} else {
rwlock_set_writers(this, rwlock_op, Scalar::from_u32(0))?;
let mut readers = 0;
while let Some(_reader) = this.unblock_some_thread(reader_blockset)? {
readers += 1;

2
src/thread.rs
View file

@ -1,8 +1,8 @@
//! Implements threads.
use std::convert::TryInto;
use std::cell::RefCell;
use std::convert::TryFrom;
use std::convert::TryInto;
use std::num::NonZeroU32;
use log::trace;