Changeset 13073be for src/libcfa

Timestamp:

May 25, 2018, 1:37:34 PM (7 years ago)

Author:

Thierry Delisle <tdelisle@…>

Branches:

ADT, aaron-thesis, arm-eh, ast-experimental, cleanup-dtors, deferred_resn, demangler, enum, forall-pointer-decay, jacob/cs343-translation, jenkins-sandbox, master, new-ast, new-ast-unique-expr, new-env, no_list, persistent-indexer, pthread-emulation, qualifiedEnum, with_gc

Children:

8dbedfc

Parents:

a1a17a74

Message:

Fix atomic builtins in libcfa and prelude

Location:

src/libcfa

Files:

• bits/locks.h (modified) (4 diffs)
• concurrency/preemption.c (modified) (4 diffs)

src/libcfa/bits/locks.h

@@ -39 +39 @@
 #endif
 
-#if __SIZEOF_SIZE_T__ == 8
-        #define __lock_test_and_test_and_set( lock ) (lock) == 0 && __sync_lock_test_and_set_8( &(lock), 1 ) == 0
-        #define __lock_release( lock ) __sync_lock_release_8( &(lock) );
-#elif __SIZEOF_SIZE_T__ == 4
-        #define __lock_test_and_test_and_set( lock ) (lock) == 0 && __sync_lock_test_and_set_4( &(lock), 1 ) == 0
-        #define __lock_release( lock ) __sync_lock_release_4( &(lock) );
-#else
-        #error unsupported architecture
-#endif
-
 struct __spinlock_t {
-        __ALIGN__ volatile size_t lock;
+        // Wrap in struct to prevent false sharing with debug info
+        struct {
+                // Align lock on 128-bit boundary
+                __ALIGN__ volatile _Bool lock;
+        };
         #ifdef __CFA_DEBUG__
+                // previous function to acquire the lock
                 const char * prev_name;
+                // previous thread to acquire the lock
                 void* prev_thrd;
         #endif
@@ -78 +74 @@
         // Lock the spinlock, return false if already acquired
         static inline _Bool try_lock  ( __spinlock_t & this __cfaabi_dbg_ctx_param2 ) {
-                _Bool result = __lock_test_and_test_and_set( this.lock );
+                _Bool result = (this.lock == 0) && (__atomic_test_and_set( &this.lock, __ATOMIC_ACQUIRE ) == 0);
                 if( result ) {
                         disable_interrupts();
@@ -94 +90 @@
 
                 for ( unsigned int i = 1;; i += 1 ) {
-                        if ( __lock_test_and_test_and_set( this.lock ) ) break;
+                        if ( (this.lock == 0) && (__atomic_test_and_set( &this.lock, __ATOMIC_ACQUIRE ) == 0) ) break;
                         #ifndef NOEXPBACK
                                 // exponential spin
@@ -112 +108 @@
         }
 
-        // // Lock the spinlock, yield if already acquired
-        // static inline void lock_yield( __spinlock_t & this __cfaabi_dbg_ctx_param2 ) {
-        //      for ( unsigned int i = 1;; i += 1 ) {
-        //              if ( __lock_test_and_test_and_set( this.lock ) ) break;
-        //              yield( i );
-        //      }
-        //      disable_interrupts();
-        //      __cfaabi_dbg_debug_do(
-        //              this.prev_name = caller;
-        //              this.prev_thrd = this_thread;
-        //      )
-        // }
-
         static inline void unlock( __spinlock_t & this ) {
                 enable_interrupts_noPoll();
-                __lock_release( this.lock );
+                __atomic_clear( &this.lock, __ATOMIC_RELEASE );
         }
 #endif

src/libcfa/concurrency/preemption.c

@@ -161 +161 @@
         void disable_interrupts() {
                 with( kernelTLS.preemption_state ) {
-                        enabled = false;
+                        static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
+
+                        // Set enabled flag to false
+                        // should be atomic to avoid preemption in the middle of the operation.
+                        // use memory order RELAXED since there is no inter-thread on this variable requirements
+                        __atomic_store_n(&enabled, false, __ATOMIC_RELAXED);
+
+                        // Signal the compiler that a fence is needed but only for signal handlers
+                        __atomic_signal_fence(__ATOMIC_ACQUIRE);
+
                         __attribute__((unused)) unsigned short new_val = disable_count + 1;
                         disable_count = new_val;
@@ -171 +180 @@
         // If counter reaches 0, execute any pending CtxSwitch
         void enable_interrupts( __cfaabi_dbg_ctx_param ) {
-                processor   * proc = kernelTLS.this_processor; // Cache the processor now since interrupts can start happening after the atomic add
-                thread_desc * thrd = kernelTLS.this_thread;       // Cache the thread now since interrupts can start happening after the atomic add
+                processor   * proc = kernelTLS.this_processor; // Cache the processor now since interrupts can start happening after the atomic store
+                thread_desc * thrd = kernelTLS.this_thread;       // Cache the thread now since interrupts can start happening after the atomic store
 
                 with( kernelTLS.preemption_state ){
@@ -181 +190 @@
                         // Check if we need to prempt the thread because an interrupt was missed
                         if( prev == 1 ) {
-                                enabled = true;
+                                static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
+
+                                // Set enabled flag to true
+                                // should be atomic to avoid preemption in the middle of the operation.
+                                // use memory order RELAXED since there is no inter-thread on this variable requirements
+                                __atomic_store_n(&enabled, true, __ATOMIC_RELAXED);
+
+                                // Signal the compiler that a fence is needed but only for signal handlers
+                                __atomic_signal_fence(__ATOMIC_RELEASE);
                                 if( proc->pending_preemption ) {
                                         proc->pending_preemption = false;
@@ -200 +217 @@
                 verifyf( prev != 0u, "Incremented from %u\n", prev );                     // If this triggers someone is enabled already enabled interrupts
                 if( prev == 1 ) {
-                        kernelTLS.preemption_state.enabled = true;
+                        static_assert(__atomic_always_lock_free(sizeof(kernelTLS.preemption_state.enabled), &kernelTLS.preemption_state.enabled), "Must be lock-free");
+                        // Set enabled flag to true
+                        // should be atomic to avoid preemption in the middle of the operation.
+                        // use memory order RELAXED since there is no inter-thread on this variable requirements
+                        __atomic_store_n(&kernelTLS.preemption_state.enabled, true, __ATOMIC_RELAXED);
+
+                        // Signal the compiler that a fence is needed but only for signal handlers
+                        __atomic_signal_fence(__ATOMIC_RELEASE);
                 }
         }