> if languages like ... can operate either at/near the performance of C
That depends entirely on how you define and measure performance. If total throughput is your metric, then it's no problem - for example, Go is perfectly acceptable for web services.
Predictability of latency, however, is absolutely _not_ on par with C code. For example, 3D rendering with a GC can easily result in perceptible stuttering if care isn't taken to minimize allocations and manually trigger the GC at appropriate times.
> some sort of symbolic annotation that allow you to manually control GC
It's not that simple. D tried to sell this at one point, but it just doesn't work for large multithreaded programs and things aren't single threaded these days. Manually controlling a global GC means manually balancing, for example, one block of threads that perform lots of allocations and deallocations (and will starve if the GC doesn't run regularly) with soft real time networking code and hard real time VR rendering code. And (for example) you certainly don't want your rendering loop pausing to scan the _entire heap_ (likely multiple gigabytes) on each frame! Alternatively, in the case of Go (and depending on your particular workload) you might not appreciate the concurrent GC constantly trashing the caches.
Custom allocators and non-atomic reference counting are fantastic though.
That depends entirely on how you define and measure performance. If total throughput is your metric, then it's no problem - for example, Go is perfectly acceptable for web services.
Predictability of latency, however, is absolutely _not_ on par with C code. For example, 3D rendering with a GC can easily result in perceptible stuttering if care isn't taken to minimize allocations and manually trigger the GC at appropriate times.
> some sort of symbolic annotation that allow you to manually control GC
It's not that simple. D tried to sell this at one point, but it just doesn't work for large multithreaded programs and things aren't single threaded these days. Manually controlling a global GC means manually balancing, for example, one block of threads that perform lots of allocations and deallocations (and will starve if the GC doesn't run regularly) with soft real time networking code and hard real time VR rendering code. And (for example) you certainly don't want your rendering loop pausing to scan the _entire heap_ (likely multiple gigabytes) on each frame! Alternatively, in the case of Go (and depending on your particular workload) you might not appreciate the concurrent GC constantly trashing the caches.
Custom allocators and non-atomic reference counting are fantastic though.