modules/audio_output/TPCircularBuffer.c

   1 //
   2 //  TPCircularBuffer.c
   3 //  Circular/Ring buffer implementation
   4 //
   5 //  Created by Michael Tyson on 10/12/2011.
   6 //  Copyright 2011-2012 A Tasty Pixel. All rights reserved.
   7
   8
   9 #include "audio_output/TPCircularBuffer.h"
  10 #include <mach/mach.h>
  11 #include <stdio.h>
  12
  13 #define reportResult(result,operation) (_reportResult((result),(operation),strrchr(__FILE__, '/')+1,__LINE__))
  14 static inline bool _reportResult(kern_return_t result, const char *operation, const char* file, int line) {
  15     if ( result != ERR_SUCCESS ) {
  16         printf("%s:%d: %s: %s\n", file, line, operation, mach_error_string(result));
  17         return false;
  18     }
  19     return true;
  20 }
  21
  22 bool TPCircularBufferInit(TPCircularBuffer *buffer, int length) {
  23
  24     // Keep trying until we get our buffer, needed to handle race conditions
  25     int retries = 3;
  26     while ( true ) {
  27
  28         buffer->length = round_page(length);    // We need whole page sizes
  29
  30         // Temporarily allocate twice the length, so we have the contiguous address space to
  31         // support a second instance of the buffer directly after
  32         vm_address_t bufferAddress;
  33         kern_return_t result = vm_allocate(mach_task_self(),
  34                                            &bufferAddress,
  35                                            buffer->length * 2,
  36                                            VM_FLAGS_ANYWHERE); // allocate anywhere it'll fit
  37         if ( result != ERR_SUCCESS ) {
  38             if ( retries-- == 0 ) {
  39                 reportResult(result, "Buffer allocation");
  40                 return false;
  41             }
  42             // Try again if we fail
  43             continue;
  44         }
  45
  46         // Now replace the second half of the allocation with a virtual copy of the first half. Deallocate the second half...
  47         result = vm_deallocate(mach_task_self(),
  48                                bufferAddress + buffer->length,
  49                                buffer->length);
  50         if ( result != ERR_SUCCESS ) {
  51             if ( retries-- == 0 ) {
  52                 reportResult(result, "Buffer deallocation");
  53                 return false;
  54             }
  55             // If this fails somehow, deallocate the whole region and try again
  56             vm_deallocate(mach_task_self(), bufferAddress, buffer->length);
  57             continue;
  58         }
  59
  60         // Re-map the buffer to the address space immediately after the buffer
  61         vm_address_t virtualAddress = bufferAddress + buffer->length;
  62         vm_prot_t cur_prot, max_prot;
  63         result = vm_remap(mach_task_self(),
  64                           &virtualAddress,   // mirror target
  65                           buffer->length,    // size of mirror
  66                           0,                 // auto alignment
  67                           0,                 // force remapping to virtualAddress
  68                           mach_task_self(),  // same task
  69                           bufferAddress,     // mirror source
  70                           0,                 // MAP READ-WRITE, NOT COPY
  71                           &cur_prot,         // unused protection struct
  72                           &max_prot,         // unused protection struct
  73                           VM_INHERIT_DEFAULT);
  74         if ( result != ERR_SUCCESS ) {
  75             if ( retries-- == 0 ) {
  76                 reportResult(result, "Remap buffer memory");
  77                 return false;
  78             }
  79             // If this remap failed, we hit a race condition, so deallocate and try again
  80             vm_deallocate(mach_task_self(), bufferAddress, buffer->length);
  81             continue;
  82         }
  83
  84         if ( virtualAddress != bufferAddress+buffer->length ) {
  85             // If the memory is not contiguous, clean up both allocated buffers and try again
  86             if ( retries-- == 0 ) {
  87                 printf("Couldn't map buffer memory to end of buffer\n");
  88                 return false;
  89             }
  90
  91             vm_deallocate(mach_task_self(), virtualAddress, buffer->length);
  92             vm_deallocate(mach_task_self(), bufferAddress, buffer->length);
  93             continue;
  94         }
  95
  96         buffer->buffer = (void*)bufferAddress;
  97         buffer->fillCount = 0;
  98         buffer->head = buffer->tail = 0;
  99
 100         return true;
 101     }
 102     return false;
 103 }
 104
 105 void TPCircularBufferCleanup(TPCircularBuffer *buffer) {
 106     vm_deallocate(mach_task_self(), (vm_address_t)buffer->buffer, buffer->length * 2);
 107     memset(buffer, 0, sizeof(TPCircularBuffer));
 108 }
 109
 110 void TPCircularBufferClear(TPCircularBuffer *buffer) {
 111     int32_t fillCount;
 112     if ( TPCircularBufferTail(buffer, &fillCount) ) {
 113         TPCircularBufferConsume(buffer, fillCount);
 114     }
 115 }