Patching TPCircularBuffer based on suggestion from landonf and maqr

OpenEmu · Apr 10, 2012 · 655ea5e · 655ea5e
1 parent fc26b00
commit 655ea5e
Showing 1 changed file with 57 additions and 41 deletions.
diff --git a/OpenEmu/TPCircularBuffer.c b/OpenEmu/TPCircularBuffer.c
@@ -38,48 +38,64 @@ static inline bool _checkResult(kern_return_t result, const char *operation, con
 }
 
 bool TPCircularBufferInit(TPCircularBuffer *buffer, int length) {
-    assert(length);
-    buffer->length = round_page(length);    // We need whole page sizes
-
-    // Temporarily allocate twice the length, so we have the contiguous address space to
-    // support a second instance of the buffer directly after
-    vm_address_t bufferAddress;
-    if ( !checkResult(vm_allocate(mach_task_self(), &bufferAddress, buffer->length * 2, TRUE /* (don't use the current bufferAddress value) */),
-                      "Buffer allocation") ) return false;
-
-    // Now replace the second half of the allocation with a virtual copy of the first half. Deallocate the second half...
-    if ( !checkResult(vm_deallocate(mach_task_self(), bufferAddress + buffer->length, buffer->length),
-                      "Buffer deallocation") ) return false;
-
-    // Then create a memory entry that refers to the buffer
-    vm_size_t entry_length = buffer->length;
-    mach_port_t memoryEntry;
-    if ( !checkResult(mach_make_memory_entry(mach_task_self(), &entry_length, bufferAddress, VM_PROT_READ|VM_PROT_WRITE, &memoryEntry, 0),
-                      "Create memory entry") ) {
-        vm_deallocate(mach_task_self(), bufferAddress, buffer->length);
-        return false;
-    }
-
-    // And map the memory entry to the address space immediately after the buffer
-    vm_address_t virtualAddress = bufferAddress + buffer->length;
-    if ( !checkResult(vm_map(mach_task_self(), &virtualAddress, buffer->length, 0, FALSE, memoryEntry, 0, FALSE, VM_PROT_READ | VM_PROT_WRITE, VM_PROT_READ | VM_PROT_WRITE, VM_INHERIT_DEFAULT),
-                      "Map buffer memory") ) {
-        vm_deallocate(mach_task_self(), bufferAddress, buffer->length);
-        return false;
-    }
-
-    if ( virtualAddress != bufferAddress+buffer->length ) {
-        printf("Couldn't map buffer memory to end of buffer\n");
-        vm_deallocate(mach_task_self(), virtualAddress, buffer->length);
-        vm_deallocate(mach_task_self(), bufferAddress, buffer->length);
-        return false;
+    // keep trying tuntil we get our buffer, needed to handle race conditions
+    while(1) {
+        buffer->length = round_page(length);    // We need whole page sizes
+                                                // Temporarily allocate twice the length, so we have the contiguous address space to
+                                                // support a second instance of the buffer directly after
+        vm_address_t bufferAddress;
+        if ( !checkResult(vm_allocate(mach_task_self(),
+                                      &bufferAddress,
+                                      buffer->length * 2,
+                                      VM_FLAGS_ANYWHERE), // allocate anywhere it'll fit
+                          "Buffer allocation") ) {
+            // try again if we fail
+            continue;
+        }
+
+        // Now replace the second half of the allocation with a virtual copy of the first half. Deallocate the second half...
+        if ( !checkResult(vm_deallocate(mach_task_self(),
+                                        bufferAddress + buffer->length,
+                                        buffer->length),
+                          "Buffer deallocation") ) {
+            // if this fails somehow, deallocate the whole region and try again
+            vm_deallocate(mach_task_self(), bufferAddress, buffer->length);
+            continue;
+        }
+
+        // Re-map the buffer to the address space immediately after the buffer
+        vm_address_t virtualAddress = bufferAddress + buffer->length;
+        vm_prot_t cur_prot, max_prot;
+        if(!checkResult(vm_remap(mach_task_self(),
+                                 &virtualAddress, // mirror target
+                                 buffer->length, // size of mirror
+                                 0, // auto alignment
+                                 0, // force remapping to virtualAddress
+                                 mach_task_self(), // same task
+                                 bufferAddress, // mirror source
+                                 0, // MAP READ-WRITE, NOT COPY
+                                 &cur_prot, // unused protection struct
+                                 &max_prot, // unused protection struct
+                                 VM_INHERIT_DEFAULT), "Remap buffer memory")) {
+            // if this remap failed, we hit a race condition, so deallocate and try again
+            vm_deallocate(mach_task_self(), bufferAddress, buffer->length);
+            continue;
+        }
+
+        if ( virtualAddress != bufferAddress+buffer->length ) {
+            // if the memory is not contiguous, clean up both allocated buffers and try again
+            printf("Couldn't map buffer memory to end of buffer\n");
+            vm_deallocate(mach_task_self(), virtualAddress, buffer->length);
+            vm_deallocate(mach_task_self(), bufferAddress, buffer->length);
+            continue;
+        }
+
+        buffer->buffer = (void*)bufferAddress;
+        buffer->fillCount = 0;
+        buffer->head = buffer->tail = 0;
+
+        return true;
     }
-
-    buffer->buffer = (void*)bufferAddress;
-    buffer->fillCount = 0;
-    buffer->head = buffer->tail = 0;
-
-    return true;
 }
 
 void TPCircularBufferCleanup(TPCircularBuffer *buffer) {